Mechanical and Viscoelastic Properties of Polylactic

Acid (PLA) Materials Processed Through Fused

Deposition Modelling (FDM)

by

Mst. Faujiya Afrose

B.Sc. (Hons) in Mechanical Engineering

A thesis submitted in fulfilment of the requirements for the degree of Master of Engineering

School of Engineering Faculty of Science, Engineering and Technology

Swinburne University of Technology Hawthorn, VIC 3122, Australia

December 2016

i

Declaration

I am declaring that the works presented in this thesis is my own work and to best

my knowledge, this work does not contain any materials which have not

previously published by any other person or submitted for the requirement of any

other degree, except where due acknowledgement and reference are provided

within the thesis. An explicit acknowledgement has been for the contribution

from any other colleagues within and outside the university.

Mst. Faujiya Afrose

05 December 2016

Declaration

ii

Abstract

Polylactic acid (PLA) is a biodegradable thermoplastic polymer and its bulk properties have

limited end use applications as the properties of materials change through its processing

methods. A great deal of attention has been paid to use PLA from packaging and biomedical

applications to structural loading applications such as in building, electrical and electronics,

furniture etc. The processing of PLA materials, mainly based on melt flow technique is time

consuming process and experienced poor surface finishing. Therefore, rapid prototyping (RP)

process has been considered for processing PLA material which fabricate physical prototype

from computer aided data (CAD) in a shorter time. The properties of PLA materials change

when processing through RP technology which has a great influence on the end use

applications.

The aim of this research is to investigate the mechanical and viscoelastic properties of PLA

material processed through fused deposition modelling (FDM) technique for end use

applications by taking account the changes of properties in three different build orientations.

In evaluating these properties, dog-boned shape and rectangular shape samples were fabricated

according to ASTM D638 and ASTM D 790 standards. To fabricate the PLA material samples

in X-, Y- and 450- build orientations, a Cube 3D FDM machine was used. Therefore, a number

of tests such as tensile, fatigue, flexural, impact, dynamic mechanical analysis (DMA) and

creep tests were conducted with Zwick Z010 and TA Instrument DMA 2980 machines to

predict the changes of properties in X-, Y- and 450- build orientations. Injection moulded

samples were also tested and to compare the results with FDM samples results.

In this study, it was found that the build orientations have great influence on mechanical

properties as well as viscoelastic properties. However, the results showed that certain build

orientation samples exhibit better properties than other build orientation samples and thus FDM

parts made in these build orientations assist in developing design guidelines for end use

applications under different loading conditions.

Abstract

iii

Acknowledgements

I would like to thank my principal coordinating supervisor, Associate Professor Pio Iovenitti

for his continuous support and guidance during my candidature. I really appreciate his help and

I was really pleased with his professionalism. He was always willing to support me despite his

extremely busy schedule.

I would also like to thank Professor Syed Masood whose guidance and suggestions were the

most valuable part parts of this work. I would not be able to publish any articles without his

support and encouragement. The help and guidance provided by Associate Professor Igor

Sbarski were helpful to get into the more insight of the research activities. I must also

acknowledge the help from Dr. Mostafa Nikzad and Mr. Warren during the experimental

activities of my research activities.

I am also grateful to my husband, Dr. Md Apel Mahmud for his continuous support. It was not

possible to start and complete the thesis without his help. I would also like to acknowledge the

help from my brother-in law for taking care of my baby during the period of my thesis writing.

At the end, I would like to thank my fellows who make my research journey enjoyable at

Swinburne University of Technology.

Acknowledgements

iv

Dedicated to my husband, my son, Faiyaz Mahmud and my parents

v

List of Publications

Journals

1. Afrose, M.F., Masood, S.H., Iovenitti, P., Nikzad, M. and Sbarski, I., 2015. Effects of part

build orientations on fatigue behaviour of FDM-processed PLA material. Progress in

Additive Manufacturing, pp.1-8.

2. Afrose, M.F., Masood, S.H., Nikzad, M. and Iovenitti, P., 2014. Effects of build

orientations on tensile properties of PLA material processed by FDM. In Advanced

Materials Research (Vol. 1044, pp. 31-34). Trans Tech Publications.

List of Publications

vi

Contents

Declaration i

Abstract ii

Acknowledgements iii

List of Publications v

List of Tables x

List of Figures xi

List of Symbols xiii

List of Abbreviations xiv

Chapter 1 Introduction 1

1.1 Overview 1

1.2 Polylactic acid (PLA) 2

1.3 Processing of Polylactic acid (PLA) 2

1.4 Properties of PLA 3

1.5 Research Project Aims 5

1.6 Contributions to New Knowledge 6

1.7 Thesis Structure 7

Chapter 2 Literature Review 9

2.1 Introduction 9

2.2 Rapid prototyping process 9

2.2.1 Stereolithography 11

Contents

vii

2.2.2 Solid base curing 11

2.2.3 Fused deposition modelling 12

2.2.4 Ballistic particle manufacturing 12

2.2.5 3D printing 13

2.2.6 Selective laser sintering 13

2.2.7 Laminated object manufacturing 14

2.3 FDM thermoplastics materials and their properties 15

2.3.1 Acrylonitrile Butadiene styrene (ABS) 15

2.3.2 Polycarbonate (PC) 17

2.3.3 Nylon 12 18

2.3.4 Acrylonitrile Styrene Acrylate (ASA) 19

2.3.5 Polyphenylsulfone (PPSF/PPSU) 20

2.3.6 ULTEM 21

2.3.7 Polylactic acid (PLA) 23

2.4 Applications of FDM thermoplastics 24

2.5 Properties of PLA 25

2.5.1 Tensile Properties 25

2.5.2 Fatigue Properties 26

2.5.3 Flexural Properties 27

2.5.4 Impact Properties 28

2.5.5 Dynamic Mechanical Properties 28

2.5.6 Creep Properties 30

2.6 Summary 30

Chapter 3 Materials and Test Methods 32

3.1 Introduction 32

Contents

viii

3.2 Materials 32

3. 2.1 Cube 2 FDM machine 33

3. 2.2 Part Fabrication by FDM 34

3. 2.3 Part Fabrication by Injection Moulding 36

3.3 Test Methods 37

3. 3.1 Tensile Test 37

3. 3.2 Fatigue Test 38

3.3.3 Flexure Test 40

3.3.4 Impact Test 40

3.3.5 DMA Test 41

3.3.6 Creep Test 43

3.4 Summary 44

Chapter 4 Mechanical Properties of FDM PLA Thermoplastic 45

4.1 Introduction 45

4.2 Tensile properties 45

4.3 Fatigue Properties 48

4.4 Impact Properties 53

4.5 Flexural Properties 55

4.6 Summary 57

Chapter 5 Viscoelastic Properties of FDM PLA Thermoplastic 58

5.1 Introduction 58

5.2 DMA Properties 58

5.3 Creep Properties 65

5.4 Summary 67

Contents

ix

Chapter 6 Conclusions and Further Research 68

6.1 Overview 68

6.2 Conclusions 68

6.3 Further Research 70

References 72

Contents

x

List of Tables

Table 1.1 Typical properties of NatureWorks PLA for extrusion and injection moulding

applications [9] 5

Table 2.1 Rapid Prototyping Process [33] 10

Table 2.2 Mechanical properties of FDM PC [49] 17

Table 2.3 Mechanical properties of FDM Nylon 12 (Conditioned) [49] 19

Table 2.4 Mechanical properties of FDM ASA [49] 20

Table 2.5 Mechanical properties of FDM PPSF [49] 21

Table 2.6 Mechanical properties of FDM ULTEM [49] 22

Table 4.1 Tensile Properties of the FDM and IM specimens 46

Table 4.2 Data outlining the average ultimate tensile stress (σu), average modulus of elasticity

and applied load in percentage of UTS 49

Table 4.3 Average impact energy and resilience of the FDM and IM specimens 54

Table 4.4 Flexural Properties of the FDM and IM specimens 56

Table 5.1. Property values of FDM and IM samples for solid normal build style 61

List of Tables

xi

List of Figures

Fig. 1.1. Relationship with stress and strain with time for pure elastic system 4

Fig. 1.2. Relationship with stress and strain with time for a pure viscous system 4

Fig. 2.1. Stress cycles in fatigue [63] 27

Fig. 2.2. a) Time Response of a sample subjected to a sinusoidal oscillating stress and its strain

response and b) Vectorial resolution of components of complex modulus [66] 29

Fig. 2.3. Creep behaviour in a system [66] 30

Fig. 3.1. Cube-2 3D FDM Machine 33

Fig. 3.2. Schematic diagram of a Cube FDM Machine 34

Fig. 3.3. Dimensions of the a) dog-bone shape and b) flat shape samples 35

Fig. 3.4. Build orientations in Cube software 36

Fig. 3.5. Representative building layer styles of the samples 36

Fig. 3.6. Battenfeld BA 350/75 injection moulding machine 37

Fig. 3.7. Specimen holding in a 10 kN Zwick machine 38

Fig. 3.8. Three point bending arrangement in a 10 kN Zwick machine 40

Fig. 3.9. Ceast Instron Impact test machine 41

Fig. 3.10. V-notched machine 41

Fig. 3.11. DMA 2980 Dynamic Mechanical Analyser 42

Fig. 3.12. Dual cantilever arrangements in a DMA 2980 Dynamic Mechanical Analyser 42

Fig. 3.13. Specimen holding for creep test in a DMA 2980 machine 43

Fig. 4.1. Average stress vs. strain graph of different orientations FDM specimens and IM

specimens 46

Fig. 4.2. Tested PLA specimens in different build orientations: (a) X-orientation, (b) Y-

orientation and (c) 45o-orientation 47

Fig. 4.3. Overview of an IM specimen: a) before test and b) after test 47

List of Figures

xii

Fig. 4.4. PLA specimens showing the pull history at 50% of the ultimate tensile stress 49

Fig. 4.5. Images of fatigue tested specimens at their 50%, 60%, 70% and 80% of UTS

respectively 50

Fig. 4.6. S-N curves for three (X, Y and 45o) orientation samples 51

Fig. 4.7. Strain energy vs. percentage of UTS for specimens in different (X, Y and 45o)

orientations 53

Fig. 4.8. Images of impact tested specimens 54

Fig.4.9. Average flexural strength vs. deformation curve for FDM and Injection moulded

specimens 55

Fig.4.10. Specimens after testing 56

Fig. 5.1. Sample for DMA and creep test: a) FDM sample and b) IM sample 58

Fig. 5.2. Temperature scan graph of loss modulus and tan delta of PLA FDM and IM samples

59

Fig. 5.3. Temperature scan graph of storage modulus and complex modulus of PLA FDM and

IM samples 60

Fig 5.4. Effect of temperature on storage modulus properties 62

Fig 5.5. Effects of temperature on loss modulus properties 62

Fig 5.6. Effect of temperature on tan delta properties 63

Fig 5.7. Effect of temperature on complex modulus properties 64

Fig 5.8. Effect of temperature on complex viscosity properties 65

Fig 5.9. Plot of percent strain against time 66

Fig 5.10. Plot of creep compliance against time 67

List of Figures

xiii

List of Symbols

𝜎𝑢 Ultimate tensile strength

𝑈 Total strain energy

𝜎 Stress

∈ Strain

𝜎a Stress amplitude

2𝜎a Range of stress variation

𝜎m Mean stress

𝜎max Maximum Stress

𝜎min Minimum stress

𝐼 Stress cycle

∆𝜎 Stress range

𝐺′ Storage Modulus

𝐺′′ Loss Modulus

𝐺∗ Complex Modulus

𝜂∗ Complex viscosity

Tan𝛿 Loss Tangent

𝜎° Maximum stress

γ ͦ Maximum strain

𝜂′ Storage viscosity

𝜂′′ Loss viscosity

𝛿 Phase lag

𝑇𝑔 Glass transition temperature

List of Symbols

xiv

List of Abbreviations

3D Three Dimensional

3DP Three-Dimensional Printing

ABS Acrylonitrile Butadiene Styrene

AM Additive Manufacturing

ASA Acrylonitrile Styrene Acrylate

ASTM American Society for Testing and Materials

BPA Bisphenol A

BPM Ballistic Particle Manufacturing

CAD Computer Aided Design

CM Complex viscosity

DOE Design of experiments

DFE Data Front End

DMA Dynamic Mechanical Analysis

FDM Fused deposition modelling

ISO International Standards Organization

LM Loss modulus

LOM Laminated Object Manufacturing

List of Abbreviations

xv

OMMT Organ Montmorillonite

PC Polycarbonate

PEI Polyetherimide

PBT Polybutylene terephthalate

PE Polyethylene

PETE Polyethylene terephthalate

PP Polypropylene

PVC Polyvinyl chloride

PLA Polylactic acid

PS Polystyrene

PPSF Polyphenylsulfone

RP Rapid prototyping

SBC Solid Base Curing

SLS Selective laser sintering

SLA Stereolithography

SM Storage modulus

TA Thermal advantage

TD Tan delta

UTS Ultimate tensile strength

List of Abbreviations

1

CHAPTER 1

Introduction

1.1 Overview

Polymers were introduced in 1940’s into the mainstream culture [1]. Subsequently, polymers

have replaced the use of metals and ceramics as polymers are less expensive and offers more

desirable properties for consumers. The use of polymers has been extended in day-by-day use

from the original polymers, such as nylon, to commodity polymers, e.g., polypropylene (PP),

polyethylene (PE), polystyrene (PS), polyethylene terephthalate (PETE), polyvinyl chloride

(PVC). These polymers are not environmentally friendly as they derived from petroleum and

the price of these polymers are rising day by day. Therefore, the manufacturers are considering

Polylactic acid (PLA) as an alternative polymer, as it is an environment friendly polymer. PLA

is one kind of a biodegradable thermoplastic polymer which is usually produced from

renewable sources, mainly from starch. It has been found that petroleum based polymers are

used to exhibit similar properties and the examples of these types of polymers are PE and

PETE. In the past decade, PLA was mainly used in packaging as well as biomedical

applications. Since PLA exhibits good properties, now-a-days the use of PLA has been

considered to extend in the sector of agriculture, building, transportation, electrical appliances

and electronics and houseware [2]. There are several applications of PLA in the biomedical

field. PLA is used as different internal body components, e.g., in ankle as interference screws,

for ligament attachment as tacks and pins, as rods and pins in bones as well as for

craniomaxillofacial bone fixation as screws and plates [3] and at the same time, it is also for

surgical sutures, implants, and drug delivery systems [[4]-[5]]. Thus in recent years,

researchers’ main concern is how the properties of PLA can be increased to achieve harmony

2

with thermoplastic processing, fabricating and endues applications. The properties of PLA can

vary when material fabricated by manufacturing processes. This research involves the study of

the properties of PLA material processed through fused deposition modelling process. This

chapter aims to present a brief overview of PLA along with the main objectives of this research.

1.2 Polylactic acid (PLA)

Polylactic acid is compostable thermoplastic polymer and belongs to the aliphatic polyesters

family which is produced from the building blocks of lactic acid (2-hydroxy propionic acid)

[6]. Such thermoplastics possess many properties which play important role in applications

requiring characteristics such as light weight, mechanical strength, transparency,

compostability, good printability, low process temperature, variable barrier properties, good

heat sealability and ease of formation into different forms. PLA was introduced with low

properties by Carothers in 1932 [7]. In 1954 and 1972, further work had been done to improve

material properties and finally, high strength PLA was introduced for medical resorbable

sutures [8]. In 1997, a joint venture between Cargill Dow LLC and Purac Biochem B.V. was

announced to commercially market PLA with an intention of reducing the production cost and

produce large scale volume of PLA [9]. Recently, PLA have been commercialized by many

companies around the world [10].

1.3 Processing of Polylactic acid (PLA)

Typically the PLA parts are processed by melt flow process and it has been experienced that

the injection moulding processed parts exhibit better properties than other manufacturing

processes. The other melt processes using PLA include dying and extrusion, stretch blow

moulding, cast film and sheet, extrusion blown film, thermoforming and foaming [6]. However,

these manufacturing processes are time consuming and further machining is required to achieve

3

surface finishing. But additive manufacturing technology enables us to achieve desired

prototypes in a shorter time with reasonable properties. For more than 20 years, additive

manufacturing (AM) technology has long been used for so called Rapid prototyping (RP)

research and development. In the rapid prototyping process, the physical part is fabricated

quickly from computer-aided data (CAD). Over time, there are lot of advancements for RP and

as a result, the costs for such processes are reducing while increasing the quality. For this

reason, the use of RP parts is increasing in many areas which include assembly match-ups,

product trials, and many other real-world applications [11]. Among all RP technologies, the

large portion of fabricating RP parts comes from fused deposition modeling (FDM). In this

research, the PLA parts are fabricated using FDM technology and a number of build parameters

are studied to investigate the effects on the material properties.

1.4 Properties of PLA

Most classical materials exhibit either elastic behaviour or viscoelastic behaviour when

subjected to an applied stress. Typically, viscoelastic behaviour is present in fluids, but in the

case of a polymer, it exhibits both elastic and viscoelastic characteristics by nature. In elastic

behaviour, an applied stress results in strain and this strain is completely recoverable when

stress is removed as shown in Figure 1.1. On the other hand, the resulting strain is not

recoverable in a viscoelastic system when the applied stress is removed so the deformation is

completely retained and some energy is lost in the system as shown in Figure 1.2. Therefore,

the determination of elastic and viscoelastic behaviour of a polymer is crucial to understanding

how a material will perform in a given application environment.

4

It has been found that the basic properties of PLA lie in-between polystyrene and PET [8]. In

this research, the elastic responses related to mechanical properties of PLA were investigated

Time t1 t2

t1 t2 Time

Stra

in

Stre

ss

Fig. 1.1 Relationship with stress and strain with time for pure elastic system

Time t1 t2

t2 t1 Time

Stra

in

Stre

ss

Fig. 1.2 Relationship with stress and strain with time for a pure viscous system

5

which include tensile, fatigue, flexural and impact behaviour, and viscoelastic properties,

which includes dynamic mechanical analysis (DMA) and creep behaviour. Table 1.1 shows the

typical properties of NatureWorks PLA for extrusion and injection moulding applications from

Cargill Dow LLC.

Properties Units PLA for

extrusion

ASTM

Methods

PLA for

injection

moulding

ASTM

Methods

Physical properties

Specific gravity g/cc 1.25 D792 1.21 D792

Melt index

(190°C/2.16 kg)

g/10

min

4-8 D1238 10-30 D1238

Clarity Transparent Transparent

Mechanical

properties

Tensile strength at

break

MPa 53 D882 48 D638

Tensile yield strength MPa 60 D882

Tensile modulus GPa 3.5 D882

Tensile elongation % 6 D882 2.5 D638

Notched Izod impact J/m 0.33 D256 0.16 D256

Flexural strength MPa 83 D790

Flexural modulus GPa 3.8 D790

1.5 Research Project Aims

This study aims to investigate the mechanical and rheological as viscoelastic properties of

thermoplastic parts processed by the FDM as well as the effect of build orientations on these

Table 1.1 Typical properties of NatureWorks PLA for extrusion and injection moulding applications [9]

6

properties. Three different build orientations of the test sample dog-bone and flat shaped

specimens were printed by using a Cube 3D printer FDM machine. These specimens were

based on ASTM standards and then cyclically tested. This study also aims to add knowledge

to the list of mechanical and viscoelastic data for PLA thermoplastic parts, which are processed

through FDM and would be high in demand in its proper applications where parts are required

to perform under different load applications.

The objectives of this research were as follow:

To investigate the effects of FDM parameters including build mode and build

orientations. In this investigation, solid build mode along with three other orientations

(X-, Y- and 45o- orientations) are used.

To assess the changes of mechanical properties of PLA specimens with different build

orientations.

To investigate the effects of build orientations on viscoelastic behaviour at different

temperature and then to characterize the material response with time-temperature.

To evaluate both mechanical and viscoelastic properties of injection moulded (IM)

PLA specimens against the FDM produced PLA specimens.

1.6 Contributions to New Knowledge Considerable research has been done on PLA composite material which is processed through

the FDM technique to investigate the material’s properties, but very few studies have been

done with FDM PLA material. Many researchers have investigated the properties of ABS, PC,

ULTEM, PPSF/PPSU thermoplastic materials. There have been written a number of articles

which have devoted to investigate the effect of process parameter on mechanical properties of

ABS parts processed through FDM including tensile, flexural, compressive and fatigue

strength [12]-[16]. Dynamic mechanical properties of ABS parts by using FDM technology

7

has been studied by many researchers [17], [18]. Other studies have investigated the effect of

FDM parameter on mechanical and viscoelastic properties with PC, ULTEM and PPSF/PPSU

materials [19]-[25]. But in the case of FDM PLA material, very few studies have been done.

There have been a number of researchers who have worked with PLA material through FDM

technology as a composite material [26], [27]. Recently the mechanical properties of PLA

materials such as tensile strength and modulus of elasticity have been investigated by changing

RepRap 3D printer [28]. However, few studies have been done on FDM PLA materials and

there is still a lack of detailed data on material properties.

This research was aimed to evaluate and analyse the mechanical and viscoelastic properties of

PLA thermoplastic parts processed through a Cube FDM machine. Samples fabricated in three

different orientations were analysed for an extensive range of material properties which provide

information to the design engineers on the making of material and material performance in its

end use applications. This study included mechanical and rheological behaviour of the PLA

material, and assessed the change of these properties in three different build orientations. These

mechanical and rheological properties predict the materials strength and durability during its

long term use application.

1.7 Thesis Structure

1.7.1. Chapter 1: Introduction

The introduction highlights the study about PLA, its basic properties and objectives behind

researching the effect of build parameters during PLA material fabrication by FDM process.

1.7.2. Chapter 2: Literature Review

In this chapter, the works done by researchers with thermoplastic materials along with PLA

thermoplastic material have been highlighted. Researchers have experimented with many

thermoplastics materials to investigate the material properties for their proper applications.

8

This review indicated the lack of knowledge about PLA properties and the importance of

investigation of PLA material properties.

1.7.3. Chapter 3: Materials and Test Methods

The material processing and experimental test methods are outlined in this chapter to analyse

the material properties. The test methods are based on the relevant Australian standards.

1.7.4. Chapter 4: Mechanical Properties of FDM PLA Thermoplastic

Mechanical properties are evaluated in this chapter to investigate the effects of build

orientations on material properties and to predict material behaviour during end use

applications. The test methods for mechanical properties include standard tests of tensile,

fatigue, flexural and impact behaviour.

1.7.5. Chapter 5: Viscoelastic Properties of FDM PLA Thermoplastic

Viscoelastic properties indicate the rheological behaviour of material during long term use and

this chapter includes standard test methods for dynamic mechanical analysis and creep

behaviour of material.

1.7.6. Chapter 6: Conclusion and Further Research

The effect of FDM parameters on the PLA material’s property have great significance during

fabricating materials for an end use application. The conclusions outline the properties

evaluated for three different orientations and their effects on the resulting properties, and

further research is identified.

9

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

Rapid prototyping (RP) technologies create three-dimensional parts directly from CAD models

by adding materials layer by layer rather than removing materials. Since no tooling or

traditional machining is required, it becomes possible to have single lot sizes at affordable

costs. Fused deposition modeling (FDM) is one of the most important RP technologies that

fabricates thermoplastic prototypes in required shapes. Typically, FDM process parts exhibit

lowered properties than its bulk material. This is a result of anisotropic behaviour of FDM

thermoplastics. Although several studies have been done to find out the materials properties of

FDM thermoplastics, little knowledge is available for FDM processed Polylactic acid (PLA)

thermoplastic. Hence, this chapter gives a brief study of all RP technologies and mainly

focusses on the literature review to investigate the properties of PLA material along with other

FDM thermoplastic materials.

2.2 Rapid prototyping process

Additive Manufacturing (AM) is a technology that enables quick fabrication of physical

models using three-dimensional computer aided design (CAD) data, which mainly used as

more accurate process in wide range of industries than conventional manufacturing process. It

offers first and effective design ideas with greater design flexibility and allows companies to

turn into successful end products rapidly and efficiently. Rapid prototyping is one of the

applications under additive manufacturing umbrella. Basically, additive manufacturing is the

whole process and rapid prototyping is the end result. Additive manufacturing as rapid

prototyping systems appeared in 1986 with the introduction of Stereolithography technology

10

[29]. In subsequent years, other technologies were introduced and fused deposition modelling

(FDM), selective laser sintering (SLS) and laminated object manufacturing are the most

common technologies. A range of different materials, plastics and composite materials are used

to design prototypes in RP technologies, (see Table 2.1). As RP techniques are increasingly

being employed to produce end-use product therefore it is important that designers are made

aware of various mechanical properties along with the viscoelastic properties of material being

produced through RP technologies. In industrial applications, many of fabricated parts are

being performed under dynamic loading application and causes failure after certain period.

Therefore, the investigation of the material properties for the AM parts still represent a fertile

area for research. However, a significant amount of research has been done to investigate the

properties of material for selective laser melting, direct metal laser sintering [[30]-[32]], but

nowadays researchers focus on studying properties of FDM materials.

Table 2.1 Rapid Prototyping Process [33]

Supply Phase

Process Layer Contribution

Technique

Phase Change Type

Materials

Liquid

Stereolithography Liquid layer curing

Photopolimerisation Photopolymers (acrylates, epoxies, colourable resins, filled resins)

Solid base curing Liquid layer curing and milling

Photopolimerisation Photopolymers

Fused deposition Modelling (FDM)

Extrusion of melted plastic

Solidification by cooling

Thermoplastics and wax

Ballistic particle manufacturing

Droplet deposition

Solidification by cooling

Polymers, wax

Powder

Three-dimensional printing

Binder droplet deposition onto powder layer

No phase change Ceramic, polymer and metal powder with binder

Selective laser sintering

Layer of powder Laser driven sintering and melting

Polymers, metals with binder, metals, ceramic and sand with binder

Solid Laminated object manufacturing

Deposition of sheet material

No phase change

Paper, polymers

11

2.2.1 Stereolithography

Stereolithography (SLA) is the oldest method of additive manufacturing where a computer

controlled moving laser beam is used to fabricate a three dimensional part from a CAD data.

This technology involves the solidification of a liquid epoxy photosensitive polymer (called

resin) in layer by layer method through the use of laser light which supplies required energy

for occurring the chemical reaction. Depending on SLA machine, the layer thickness varies

from 0.025 to 0.15 mm The SLA machines are relatively inexpensive and have a great surface

finish in comparison to other rapid prototyping technologies. The process was first introduced

as rapid prototyping in 1986 by Charles Hull, co-founder of 3D Systems [29]. It is an ideal

solution to create oddly shaped prototypes with higher accuracy that prototypes are difficult to

produce by using traditional prototyping methods. Liquid photopolymers such as elastomer,

urethane, epoxy, acrylate and vinyl ether are used as build materials. Though strength can be

increased by increasing layer thickness in SLA technology but typical tensile strengths up to

75 MPa can be achieved, depending on material used [34]. Many industries, from medical to

manufacturing use SLA to build prototypes and on occasion, final products.

2.2.2 Solid base curing

Solid Base Curing (SBC) processes are suitable for building multiple parts with different

geometry and dimensions in batch production of rapid prototypes [35]. In SBC, parts are built

in layer by layer method from a liquid photopolymer resin which solidifies during exposed to

UV light through a mask. The musk is created from the CAD data input. Cubital’s Solider DFE

(Data Front End) software is used to format CAD files into STL files. The manufacturer of

SBC systems are Cubital Ltd. Israel, Cubital America Inc., USA and Cubital GmbH, Germany.

Cubital Ltd. Operations began in 1987 as a spin-off from Scitex Corporation and

commercialised in 1991. However, parallel processing is the main advantage of SBC but

12

problems in model accuracy, quality, and material properties of prototypes limit their

applications. Conceptual design presentation, engineering testing, design proofing, functional

analysis, tooling and casting, moulding, medical imaging are the applications of SBC [36].

2.2.3 Fused deposition modelling

Fused deposition modelling is one of the most commonly used RP technologies. The very first

3D rapid prototyping part through FDM was introduced in April, 1992 [37]. The Stratasys Inc

is the main manufacturer of FDM machines. In the FDM process, a 3D printer is used to build

parts in a layer-by-layer manner by extruding semi-molten thermoplastic materials through a

nozzle according to a computer-controlled path. Now multi-nozzle system in FDM have been

developed, where different types of materials extrude through each nozzle in order to fabricate

prototypes with novel properties [38]-[40]. The build material is supplied in FDM as filament

coils (diameter 1.5 mm). Commonly, wax, elastomers and a number of thermoplastics are used

as the build material. The FDM processed parts exhibit anisotropic properties not only

regarding the raster orientation, but also with reference to the build orientation [41]. Typically

tensile strength is approximately two-thirds of the strength of the same thermoplastic that has

been injection-moulded [34]. Aerospace interior components to automotive parts, medical

implants, customised consumer components and sporting goods are the current and potential

applications of FDM systems [42].

2.2.4 Ballistic particle manufacturing

The ballistic particle manufacturing (BPM) technique is a rapid prototyping technique where a

piezo-driven inkjet mechanism is used to shoot droplets of melted materials onto a formerly

deposited layer. In BPM process, a droplet nozzle which moves in x and y direction is used

for creating layers. BPM process is capable of building parts from a lower toxic stand point

with minimum post processing. Perception Systems and Automated Dynamics Co have

13

developed BPM systems. Typically, thermoplastics, aluminium, and wax are usually used these

materials as these can easily be melted and solidified. The BPM process offers overall accuracy

around 0.004 inch with a layer thickness of 0.0035 inch. The typical use of BPM parts include

concept visualization which provide valuable insights to the visualization aspects.

2.2.5 3D printing

Three-Dimensional Printing (3DP) is a RP process where a 3D part is built with several layers

on top to each other in a layer by layer method until the entire object is created. Each of these

layers are very thin (10 – 200 μm is a common range) and can be seen as a thinly sliced

horizontal cross-section of the final object. In 3D printing, an inkjet printing head is used to

spray a liquid binder into a power layer and laterally the binder solidified in to a solid layer. In

order to print 3D part, a CAD model is converted into slices to represent the layers and sent to

the machine to print the part. Recently a software solution “Magic” has been developed to

prepare the CAD files for 3D Printing [43]. The use of a variety of materials is the unique

benefit of 3D printing. The available material options are ranging from plastics to metals,

ceramics and even edible substances like chocolates. The 3D Systems and Z Corporation are

the major manufacturer of 3D printing machines [44]. Surgical guides, hearing aids, spare parts

on demand and consumer goods are the major applications of 3D printing technologies [43].

2.2.6 Selective laser sintering

In selective laser sintering (SLS) or laser sintering (which is an AM process), a desired three-

dimensional shape is obtained from a CAD model using a laser beam where this laser beam is

used to fuse and sinter the polymer particles. The fusing and sintering of the polymer particles

is done through the scanning of the cross-sections on a powder-surfaced bed in a layer-by-layer

manner to form the desired object. The thickness of the layer is increased by one after scanning

each cross-section while power bed is lowered by the same scale. Similarly, the thickness of

14

layer is increase with new layer after another scanning and the process will continue until the

desired part is built. The SLS process has the ability to build parts from a variety of powder

materials which include polymers, metals, polymer or glass composites, ceramics, metals, and

polymer or metal powder [[45] & [46]]. In SLS, there are different binding mechanisms such

as chemically induced binding, solid state sintering, liquid phase sintering, and partial melting

[47]. The polymer coating or mixed polymer particles serves as the binder for building parts

from metals or ceramics using SLS process. Fully sintered parts are obtained from the post

processing while the binder is also removed. Since parts are fabricated in the surroundings of

uninterred powder, the SLS process does not need any structural support like other AM

processes, e.g. SLA and FDM. 3D system and EOS are the main manufacturers for

commercializing SLS equipment [44]. End use of functional parts, product concept models,

rapid tooling, patterns, mould and cores for casting, medical and dental implants, models for

ergonomic testing and snap fits and hinges are the applications of SLS technologies [34].

2.2.7 Laminated object manufacturing

The sheets form of solid materials is used in the Laminated Object Manufacturing (LOM)

process. In this process, a cross-section in the sheet is cut first which is then attached to the

desired part to be built. A moveable substrate is used across which the material sheet is spread

over. A laser is used to cut the sheet based on a CAD model to obtain the desired shape of the

part. The layers are then tied up through the compression of the sheet using a hot roller as well

as activating a heat sensitive glue. The materials obtained from this process can be layers of

different glue-coated papers, plastics, or laminated metals. The faster fabrication speed is the

main advantage of the LOM process as it requires to scan only the shape of the part rather the

whole cross-section as in the SLS process [48]. The major manufacturer of LOM was Helisys

Inc. (USA) and recently, it has been replaced by Cubic Technologies as Helisys Inc. (USA) is

15

now out of business [44]. Large product concept models, non- functional prototypes, casting

patterns and cores and tooling models are the typical applications of LOM technologies [34].

2.3 FDM thermoplastics materials and their properties

The properties of thermoplastic materials of FDM parts plays an important role during design

verifications and effects on the testing results. The main FDM thermoplastics are Acrylonitrile

Butadiene Styrene (ABS), Polycarbonate (PC), Nylon, Acrylonitrile Styrene Acrylate (ASA),

Poly-lactic acid (PLA), Polyphenylsulfone (PPSF) and ULTEM (a family of Thermoplastics

Polyetherimide (PEI)). Although the data of all thermoplastics except PLA are available on

Stratasys Inc, PLA is not yet listed and there still remains room for research.

2.3.1 Acrylonitrile Butadiene styrene (ABS)

ABS is a most widely employed engineering thermoplastic material, because of its low cost

and fabricates structural rapid prototyping parts. The compositions of ABS are about half of

styrene with a balance divided between butadiene and acrylonitrile. Due to its possible

variation, many blends along with other material have been developed. The properties of ABS

types have already listed in Stratasys Inc [49]. It is ideal for automotive hardware, appliance

cases, pipes, plated items and electroplated metal coating for decorative hardware. Since FDM

is one of the most important and widely used technologies, it has been found many studies

related to properties with ABS. The Taguchi method is applied to study the effect of process

parameters on the mechanical properties of the ABS prototype [12]. In [13], the researchers

have been performed tensile and flexural tests with ABS and a very simple finite element model

have been presented. It has been found that the mechanical properties of the final ABS parts

depend on the chosen building orientation and the chosen path. Some other researchers have

investigated the tensile strength and compressive strength of FDM ABS P400 by using design

of experiments approach such as (raster orientation, air gap, bead width, color and model

16

temperature) and compared with injection moulded ABS P400 [14]. In these studies, the parts

were fabricated by FDM 1650 and tested by Instron 8872 with 25 KN load cell. For the FDM

parts, the tensile strength in [450/-450] and [00/900] raster orientations ranged between 65 to 72

percent of injection moulded parts and the compressive strength in [00] and [900] raster

orientations ranged between 80 to 90 percent of injection moulded parts. As a result several

build rules were formulated to obtain better strength. In another study, the authors have

investigated the fatigue data for several print orientations of ABS and ABSplus materials [15].

In this study, ABS (P400) material was printed by using Stratasys ® Dimension which

introduced in 2002 and the newer ABSplus (P430) was printed by using the Dimension Elite.

In [16], the tensile tests with ABS FDM parts were performed to maximize the tensile strength

by controlling contour number. Therefore, in this work contour number along with five

important process parameters such as layer thickness, raster width, part orientation, raster angle

and air gap are considered and their effects on tensile strength of FDM built parts are studied.

The authors have investigated the dynamic mechanical properties of ABS parts by using a FDM

vantage machine to print the ABS specimens and a DMA 2980 machine to experiment the

specimens [17]. In this work, by considering the effects of FDM parameters, a frequency sweep

method is performed to determine the dynamic mechanical properties such as storage modulus,

damping and viscosity values. As many studies have been done on ABS and their properties

through FDM is also available [49], now researchers focus on the composite material

properties. Recently ABS nanocomposites have been characterised with organ montmorillonite

(OMMT) [18]. In this study, ABS nanocomposites were prepared by melt intercalation, and

filaments were produced by a single screw extruder and nanocomposite sample were printed

by a commercial FDM 3D printing machine. Finally, the samples were tested to characterise

the mechanical and dynamic mechanical behaviour.

17

2.3.2 Polycarbonate (PC)

Polycarbonate is one kind of engineered thermoplastic which produced from long-chain linear

polyesters of carbonic acid and dihydric phenols such as bisphenol A (BPA). It is available in

different grades and also used in compounds or blended with other materials such as

acrylonitrile butadiene styrene (ABS) or polybutylene terephthalate (PBT). It has excellent

physical properties, excellent toughness and very good heat resistance. It is used in optical

media, medical equipment, the electrical, electronic and automotive industries and glazing and

sheet sectors. As it is transparent and weighs much less than glass it also use as eyeglasses.

Although the data for PC through FDM is listed in Stratasys Inc. (see Table 2.2), several studies

have been performed to investigate the characteristics of FDM PC parts.

Table 2.2 Mechanical properties of FDM PC [49]

Mechanical Properties

Test Methods

Units

XZ Axis

ZX Axis

Tensile Strength, Yield

(Type 1, 0.125”, 0.2”/min)

ASTM D638 MPa 40 30

Tensile Strength, Ultimate

(Type 1, 0.125”, 0.2”/min)

ASTM D638 MPa 57 42

Tensile elongation, at Break

(Type 1, 0.125”, 0.2”/min)

ASTM D638 % 4.8 2.5

Tensile Modulus (Type 1,

0.125”, 0.2”/min)

ASTM D638 MPa 1,944 1,958

Flexural Strength (Method

1, 0.05”/min)

ASTM D790 MPa 89 68

Flexural Modulus (Method

1, 0.05”/min)

ASTM D790 MPa 2,006 1,800

IZOD Impact, Notched

(Method A, 23°C) ASTM D256 J/m 73 28

18

In [19], an experimental work has been done with a Zwick Z010 machine to do tensile test with

PC FDM parts. This study shows the results of the experimental work while considering the

influence of the FDM process parameters such as air gap, raster width, and raster angle on the

tensile properties of PC parts. The conclusion of this study is that the tensile strength of the

FDM made parts ranged of 70 to 75 % of the moulded and extruded PC parts. On the other

hand, dynamic mechanical properties of FDM processed polycarbonate (PC) parts have been

studied running isothermal frequency sweeps between 10 and 100 Hz [20]. In this work,

parameters (built style, raster width, and raster angle) have been studied. Built style (part

interior style in Insight ® FDM control software) refers to sets of parameters named as solid -

normal, sparse, and sparse - double dense. In [21], a Taguchi approach method and an analysis

of variance (ANOVA) have been performed to identify the most significant parameters and

levels that effects the dynamic performance of the FDM processed PC specimens. Therefore,

in this study, the results obtained for PC parts has been made by using a Fortus 400mc FDM

machine and tested with a DMA Q800 TA to investigate the effects of FDM process

parameters. In [22], the authors have performed physical tests on FDM parts, and then

correlated the results with the finite element analysis. The authors designed a simple part and

fabricated the part in different orientations to be physically tested in combined loading

including bending and torsion and simulated to correlate with physical results.

2.3.3 Nylon 12

Nylon is a synthetic thermoplastic polymer which was the first commercial thermoplastic used

in 1938 [50]. Nylon thermoplastics are used in additive manufacturing (AM) through fused

deposition modelling (FDM) and selective laser sintering (SLS). Among of them, nylon 12, the

first nylon designed special for Fortus 3D FDM machine, which is aimed to require repetitive

snap fits, high fatigue endurance, strong chemical resistance, high impact strength or press-fit

19

inserts [42]. The new nylon material is “popular in traditional manufacturing for its superb

price-performance”. Nylon parts built on FDM technology exhibit 100% to 300% better

elongation at break and high fatigue resistance over any other additive manufacturing [49].

Recently, researchers have been using Nylon 12 to produce Nylon 12 composite powder

material for use in automotive and electronics manufacturing applications [51]. Also, it offers

high fatigue endurance and high impact strength is ideal for aerospace and automotive

applications including custom tooling, jigs and fixtures, and interior panelling prototypes. A

series of data is available for Nylon 12 in Stratasys Inc (see Table 2.3).

Table 2.3 Mechanical properties of FDM Nylon 12 (Conditioned) [49]

Mechanical Properties

Test

Methods

Units

XZ Axis

ZX Axis

Tensile Strength, Yield (Type 1, 0.125”,

0.2”/min)

ASTM D638

MPa 32 28

Tensile Strength, Ultimate (Type 1, 0.125”, 0.2”/min)

ASTM D638

MPa 46 38.5

Tensile elongation, at Break (Type 1, 0.125”,

0.2”/min)

ASTM D638

% 3.0 5.4

Tensile Modulus (Type 1, 0.125”, 0.2”/min)

ASTM D638

MPa 1282 1138

Flexural Strength (Method 1, 0.05”/min)

ASTM D790

MPa 67 61

Flexural Modulus (Method 1, 0.05”/min)

ASTM D790

MPa 1276 1180

IZOD Impact, Notched (Method A, 23°C)

ASTM D256

J/m 135 53

2.3.4 Acrylonitrile Styrene Acrylate (ASA)

Acrylonitrile styrene acrylate is a production-grade thermoplastic that was first introduced by

BASF in 1970 [52]. It is available in 10 fade-resistant colors and suitable for FDM Technology.

20

It offers combined mechanical strength and UV stability with outstanding aesthetics. Its UV-

resistance makes it especially suited in end-use parts for outdoor commercial and infrastructure

use. According to [49], its wide selection of colors and matte finish makes it ideal for attractive

prototypes in consumer sporting goods, tools and automotive components and accessories.

Table 2.4 presents the mechanical properties that are listed in the Stratasys Inc. website.

Table 2.4 Mechanical properties of FDM ASA [49]

Mechanical Properties

Test

Methods

Units

XZ Axis

ZX Axis

Tensile Strength, Yield (Type 1, 0.125”,

0.2”/min)

ASTM D638

MPa 29 27

Tensile Strength, Ultimate (Type 1, 0.125”, 0.2”/min)

ASTM D638

MPa 33 30

Tensile elongation, at Break (Type 1, 0.125”,

0.2”/min)

ASTM D638

% 9 3

Tensile Modulus (Type 1, 0.125”, 0.2”/min)

ASTM D638

MPa 2,010 1,950

Flexural Strength (Method 1, 0.05”/min)

ASTM D790

MPa 60 48

Flexural Modulus (Method 1, 0.05”/min)

ASTM D790

MPa 1,870 1,630

IZOD Impact, Notched (Method A, 23°C)

ASTM D256

J/m 64 XX

2.3.5 Polyphenylsulfone (PPSF/PPSU)

Polyphenylsulfone is a high performance thermoplastic that offers outstanding heat resistance

and excellent chemical resistance than any other FDM thermoplastic materials. PPSF parts are

not only mechanically superior (see Table 2.5), but also dimensionally accurate [53]. It is

21

sterilisable via gamma, Eto, plasma, chemical and autoclave. It has the ability to produce real

parts direct from digital files that are ideal for conceptual modelling, manufacturing tools,

functional prototypes, and end-use parts applications [49]. However, very limited work has

been done on the properties of PPSF material through the FDM technology. Recently the

dynamic mechanical behaviour has been investigated on PPSF thermoplastic materials [23].

This study is based on Taguchi method to achieve better damping properties and focuses on

understanding the influence of three major parameters such as raster angle, raster width and

build style on the mechanical behaviour under dynamic loading. A DMA 2980, dynamic

mechanical analysis apparatus had been used with sweeping temperature at three different

frequencies, e.g., 1 Hz, 50 Hz and 100 Hz.

Mechanical Properties

Test Methods

Units

PPSF

Tensile Strength, Yield (Type 1, 0.125”, 0.2”/min)

ASTM D638 MPa 55

Tensile Modulus (Type 1, 0.125”, 0.2”/min)

ASTM D638 MPa 2,100

Tensile elongation, at Break (Type 1, 0.125”, 0.2”/min)

ASTM D638 % 3

Flexural Strength (Method 1, 0.05”/min)

ASTM D790 MPa 110

Flexural Modulus (Method 1, 0.05”/min)

ASTM D790 MPa 2,200

IZOD Impact, Notched (Method A, 23°C)

ASTM D256 J/m 58.7

2.3.6 ULTEM

ULTEM is an amorphous thermoplastic polyetherimide (PEI) material which offers excellent

mechanical strength, outstanding heat resistance, high dielectric strength and stability and

exceptional resistance to environmental forces [54]. Natural ULTEM, is a translucent amber

Table 2.5 Mechanical properties of FDM PPSF [49]

22

material with addition of glass fibre reinforced the ULTEM which provides greater tensile

strength and rigidity along with improving dimensional stability. Generally, these unique

properties make ULTEM materials an excellent choice for the commercial industries-

especially in automotive, marine, aircraft, medical, microwave, and electrical/electronic

industries. ULTEM 1010 and ULTEM 9085, two reinforced ULTEM that processed through

FDM are high performance thermoplastics for digital manufacturing and rapid prototyping.

Table 2.6 Mechanical properties of FDM ULTEM [49]

Few published research works have been done on ULTEM to characterise its properties through

FDM. The authors have investigated the effects of build orientation and tool path generation

on the tensile properties of FDM processed ULTEM 9085 material [24]. Therefore, the

specimens used for tensile tests were fabricated in X, Y and Z directions to study the tensile

strength of FDM parts. In [25], the authors have investigated the dynamic mechanical

properties on ULTEM 9085 with FORTUS 900 mc from Stratasys. In this study, ULTEM parts

Mechanical Properties Test Methods Units ULTEM 1010 ULTEM 9085

Tensile Strength, Yield, (Type 1, 0.125”, 0.2”/min)

ASTM D638 MPa 64 33

Tensile Strength, Ultimate, (Type 1, 0.125”, 0.2”/min)

ASTM D638 MPa 81 42

Tensile elongation, at Break, (Type 1, 0.125”,

0.2”/min)

ASTM D638 % 3.3 2.2

Tensile Modulus, (Type 1, 0.125”, 0.2”/min)

ASTM D638 MPa 2770 2270

Flexural Strength, (Method 1, 0.05”/min)

ASTM D790 MPa 144 68

Flexural Modulus, (Method 1, 0.05”/min)

ASTM D790 MPa 2820 2050

IZOD Impact, Notched, (Method A, 23°C)

ASTM D256 J/m 41 48

23

were fabricated using solid normal build style and three values each of raster width and raster

angle in a Stratasys FORTUS 900 mc FDM machine and tested in a DMA 2980 with

temperature sweep at three different fixed frequencies. This study concludes that the FDM

parameters (raster angle and raster width) affects the dynamic mechanical properties. Stratasys

Inc presents the data of ULTEM for design engineers for proper applications (see Table 2.6).

2.3.7 Polylactic acid (PLA)

Polylactic acid (PLA) is a biodegradable thermoplastic polymer which can be produced

from lactic acid. Since PLA is an environmentally friendly polymer, it is the most successful

biodegradable polymer with a global market in excess of 200,000 tonnes per annum and

projected growth rates over 15% [55]. As it is dimensionally stable, it is ideal for RepRap FDM

technology. Typically, PLA is relatively inexpensive and harder than ABS. It possesses high

mechanical strength, good crease-retention, grease and oil resistance and excellent aroma

barrier properties [56]. It is ideally suited in high volume commodity markets such as

automotive, fibres and consumer durable goods. Although it offers superior properties

compared to the other commercial polymers, its properties for FDM technology are not listed

in detail even on the Stratasys’ materials website. Also, while there have been some studies of

mechanical properties of well-known additive manufacturing materials such as ABS and PC,

PLA has received very little attention. In the published literature, some researchers have

investigated the mechanical properties of PLA as composite materials, with many fibres added

[26], [27]. Recently the mechanical properties such as tensile strength and modulus of elasticity

of PLA materials have been investigated by changing RepRap 3D printer slicing variables [28].

It is noted that the properties of FDM processed PLA has not yet been addressed by researchers

in published work.

24

Therefore, in this present study, the objective is to investigate the mechanical and

viscoelastic behaviour of FDM processed PLA materials through the use of flat dog-bone

specimens under tensile fatigue loading. In this work, an FDM process type Cube 2nd

generation 3D printer is used to produce the dog-bone shape tensile samples in X-, Y- and 45o-

build orientations. A Zwick Z010 universal testing machine and a DMA 2980 machine are

used to conduct testing of FDM parts. The effect of build orientation is investigated to

understand the characteristics of the PLA parts to obtain data helpful in design of such parts

subjected to desire applications. As higher compressive strengths are often observed in

polymers [14], so it is not investigated in this study. However, other mechanical properties

such as fatigue, flexural, impact and viscoelastic properties are investigated experimentally in

this present work.

2.4 Applications of FDM thermoplastics

Because of light weight, ease fabrication of complex geometry and low cost thermoplastics

have been developed at a significant pace. Their application to industrial structural parts has

accelerated in the past forty years. Because of their lower mechanical properties as compared

with metals, thermoplastics were not considered as engineering materials in past two decades.

The increasing use of low cost polymeric materials in consumer and automotive industries were

introduced in early 1980s. Although the load-bearing parts in industry are common engineering

applications of thermoplastics [57], nowadays, the trend of using thermoplastics are growing

in biomedical and tissue engineering fields such as novel scaffold architectures [58] and

knotless suture anchor [59]. Recently, researchers focused on extending the applicability (such

as electromagnetic and X-ray shielding) of FDM thermoplastics by developing materials [60].

The typical applications in which thermoplastics widely used are below:

Engineering materials as used in various technical applications (e.g., seals, gaskets,

damping elements, and membranes)

25

Rapid tooling

Packaging materials

Medical models

Functional prototypes, e.g. for experimental testing, wind tunnels, etc.

Product concept models

Patterns and cores for casting processes

LEGO applications

Consumer goods

Aerospace

2.5 Properties of PLA

2.5.1 Tensile Properties

Typically, the tensile strength of polymer is lower than metals and ceramics. The tensile

strength of a material is the ability to withstand breaking when the material is subjected to

tensile load. It is important to measure the tensile properties of materials for its structural

applications. The test for thermoplastic polymer to measure tensile properties is according to

ASTM D638 or ISO 527. From the test results, one can calculate ultimate tensile strength,

tensile yield strength, ultimate elongation and tensile modulus of the material. If the tensile

modulus is high (rigid material), then that means more stress is needed to produce that amount

of strain. As PLA is a rigid polymer, its ultimate elongation often exhibits values under 5%.

Typical tensile properties like tensile strength, ultimate tensile elongation of PLA can be found

in [61]. The greater values of tensile properties lead to polymers with high toughness.

26

2.5.2 Fatigue Properties

Fatigue occurs when parts are subjected to under cyclic loading applications is the main

concern in case of designing polymeric components for structural employments. Typically, in

the testing environment polymers are more sensitive than metals and ceramics. Therefore, a

number of parameters that control the fatigue life of polymer are considered for the safe design

of the polymeric components while undergoing cyclic loading. These parameters include stress,

strain, mean stress, stress concentrations, temperature, frequency and test environment. The

total number of life prediction cycles is the main consideration to the design engineer while

designing polymeric components to perform in cyclic loading applications. If the fatigue life

cycles are less than 105, then it is considered as low fatigue material and if the fatigue life

cycles is greater than 105, then it considered as high fatigue material. In general, thermoplastics

are in the low cycle fatigue material range, and in the case of ABS, it exhibits less than 105 life

cycles [15]. Traditionally, the fatigue life prediction is based on the endurance limit which

established from S-N curves [62]. In fatigue testing, the alternating stress and mean stress are

shown in Figure 2.1 and determined by the below equations.

Stress range, ∆𝜎 = 𝜎max − 𝜎min

Alternating stress, 𝜎a =∆𝜎

2=

𝜎max − 𝜎min

2

Mean stress, 𝜎m =𝜎max + 𝜎min

2

27

2.5.3 Flexural Properties

A typical flexural test involves a rectangular shape specimen holds on a support span and load

is applied to the center of the specimen producing three-point loading mode. Actually, it

measures the force required to bend the material under three-point bending condition. The

properties of flexural tests are the same as the tensile test like ultimate flexural strength,

ultimate flexural elongation and flexural modulus. These properties are often used to select

materials for parts which will resist bending during loading. Usually flexural modulus is used

to measure the materials stiffness undergoing bending. The flexural test of polymer is

performed according to either ASTM D790 or ISO 178. In the case of ASTM D790, the

ultimate elongation occurs under values of 5% deflection and for ISO 178, the ultimate

elongation occurs under values of 3.5% deflection Typically, a PLA thermoplastic polymer

exhibits better flexural properties than polystyrene [8]. In this research, the flexural test is

relevant to ASTM D790.

Time 𝑡

Stre

ss 𝜎

𝜎m

𝜎a 2𝜎a

𝜎min

𝜎max

∆𝜎

=𝜎

ma

x−

𝜎m

in

𝐼

𝜎a Stress amplitude 2𝜎a Range of stress variation 𝜎m Mean stress 𝜎max Maximum Stress 𝜎min Minimum stress 𝐼 Stress cycle

Fig.2.1 Stress cycles in fatigue [63]

28

2.5.4 Impact Properties

Many polymers exhibit excellent characteristics in terms of impact strength. Impact strength is

determined by applying a sudden load on a material and represents the ability of the material

to withstand the loading condition. The ability of materials to withstand an impact or sudden

deformation without breaking is usually described through the toughness. There is not a single

or universal test which can predict the impact characteristics of plastic materials under different

loading conditions which a part may need to face. There are some materials whose impact

strength may be reduced if the temperature is lowered. Thermosets and reinforced

thermoplastics do not change much with changes in temperature. Notches are machined into

the specimen to standardise the impact results against stress concentrators within the plastic

and to assess the sensitivity to weakening [64].

2.5.5 Dynamic Mechanical Properties

Using Dynamic Mechanical Analysis (DMA), the mechanical properties of materials are

measured as a function of temperature, frequency and time, and it is also a thermal analytical

method where an oscillating force is usually applied to a material sample to analyse the

responses corresponding to that particular force. Actually, it determines the basic structural

properties of polymeric material. However, DMA may not be able to distinguish between a

semi-crystalline and an amorphous material, but it provides quantitative data to design new

structural prototype in order to make the best use. DMA data are used to calculate different

properties such as the viscosity which is also called the tendency to flow from the phase lag

and the stiffness as modulus from the sample recovery. These properties are then described as

damping when they have the ability to loose energy in the form of heat and as the elasticity

which represents the ability of materials to recover from deformation. In DMA analysis, when

29

an oscillatory force is applied to the sample; a sinusoidal stress is originated due to this applied

force which in turns generates a sinusoidal strain as shown is Figure 2.2.

Different dynamical properties such as modulus, viscosity and damping can be calculated from

the measurement of the deformation amplitude at the peak of the sine wave as well as from the

laggings of sinusoidal stress and strain curves. In the case of amorphous glassy polymers to

semicrystalline highly crystalline, the glass transition temperature of PLA polymers ranges

from 60°C and the ranges of melting points for crystalline are from 130 to 180°C [8]. The

theoretical approaches are summarised as follows,

Storage Modulus, 𝐺′ = (𝜎°/𝛾°)𝑐𝑜𝑠𝛿

Loss Modulus, 𝐺′′ = (𝜎°/𝛾°)sin𝛿

Complex Modulus, 𝐺∗ = 𝐺′+i𝐺′′ = 𝜎°/𝛾°

Complex viscosity, 𝜂∗ = 𝜂′ − 𝑖𝜂′′

Loss Tangent, tan𝛿 = 𝐺′′/𝐺′

where

𝜎° = Maximum stress

0 2 4 6-1

-0.5

0

0.5

1

Time

Forc

e

Phase lag, δ

Strain

Stress

a)

𝐺∗

𝐺′

𝐺′′

b)

𝛿

Fig. 2.2 a) Time Response of a sample subjected to a sinusoidal oscillating stress and its strain response and b) Vectorial resolution of components of complex modulus [66]

30

γ ͦ = Maximum strain

𝜂′ =Storage viscosity

𝜂′′=Loss viscosity

𝛿 = Phase lag

2.5.6 Creep Properties

The creep property of a material is one of the most fundamental form of polymer behaviours

which is directly used to analyse the performance of products. When creep occurs in a polymer,

it is in failure mode with an indication of poor design of the materials which is a usually fact

of life [65]. The creep experiment shows a material’s response over a constant loading

condition along with its behaviour when the load is removed. The creep experiment can also

be used to collect data at very low frequencies, under long test times, or under real-time

conditions [66]. The creep behaviour of a system is shown in Figure 2.3.

2.6 Summary

This chapter highlights the previous research on the properties of materials used in the FDM

process parts that has been carried out to investigate mechanical and viscoelastic properties of

FDM thermoplastics. It was found that FDM processed parts exhibit anisotropic properties [41]

Time

Stress Strain

Stre

ss, 𝜎

Stra

in, 𝛾

Fig. 2.3 Creep behaviour in a system [66]

31

and shows lower properties as compared with injection moulded parts. Also, because of no

tooling requirement, and the capability of accurately producing complex geometry that have

been used as end use of functional parts, FDM parts play a key role in many industrial

applications.

Many researchers have studied the mechanical behaviours of uniaxial tensile specimens under

static loading and also a few studies have characterised the viscoelastic properties (dynamical

mechanical behaviours) of FDM parts. However, the majority of these studies have focused on

determining properties of new materials which need to be used in the FDM process [67]-[69].

Many researchers have carried out studies on FDM processed thermoplastics and that material

property data of these thermoplastics have been published, however, PLA has not been

researched fully and data are not available on Stratasys Inc website nor published elsewhere.

Hence, we conclude that there still remains room for research on PLA.

In subsequent chapters of this thesis, the mechanical and viscoelastic behaviours of FDM

processed PLA materials have been investigated through the use of flat dog-bone specimens

under tensile fatigue loading. The 2nd generation of a Cube 3D printer is used to produce dog-

bone shapes in X-, Y- and 45o build orientations which are then used as tensile samples. A

Zwick Z010 universal testing machine and a DMA 2980 machine are used to conduct testing.

Different build orientations are considered to understand the characteristics of the PLA parts

as well as to obtain useful data for different design purposes. In addition, this thesis also

includes the experimental investigations of other mechanical properties such as fatigue,

flexural, impact and viscoelastic properties.

32

CHAPTER 3

Materials and Test Methods

3.1 Introduction

This chapter describes the sample processing technique and the test methods applied

throughout the research. PLA cartridges were used to build test samples through the Cube-2

FDM machine in three different build orientations. In the Cube-2 FDM machine, PLA

filaments were extruded in a layer by layer manner by extruding semi-molten PLA

thermoplastic through the nozzle of cube machine. These extruded filament was solidified in

three different build orientations to process test samples for the purpose of mechanical and

rheological testing.

3. 2 Materials

In this study, Polylactic acid (PLA) cartridges were used as raw materials for FDM machine.

The PLA cube cartridges were made in USA by 3D Systems Inc. [70]. The filament material

in the cartridges that work with the Cube comes in 16 different colours and can print a

maximum 13 to 15 medium size samples from a single cartridge. In this research, white and

black colour cartridges were used to print the FDM specimens. On the other hand, in case of

IM machine the raw material was starch based PLA resin produced by BIOTEC, a subsidiary

company of Biome Technologies. It was supplied by BioPak Pty Ltd Australia in granule which

is known as Bioplast GS2189 (Biotec). This compound polymer is composed of 90% corn-

derived PLA and reinforced with 10% potato starch [71].

33

3. 2.1 Cube 2 FDM machine

Cube-2 3D printer Fused Deposition Modelling (FDM) technique was employed to

fabricate the test samples. The Cube 3D (2nd generation) printers are based on FDM type

plastic jet printing technology and made in USA by 3D Systems Inc. [70]. It comes with a

single print jet, filament material cartridge; cube tube, cube glue stick and a print pad with a

maximum build envelope size of 140 mm x140 mm x 140 mm as shown in Fig.3.1.

Fig. 3.1. Cube-2 3D FDM Machine

The Cube does not require any support when part features are not angled more than 45o in the

print platform. Also, it allows moving the print jet and the platform together in X, Y and Z

directions. The cube offers wireless network and USB connectivity. In order to build a part,

Cubify software converts the 3D STL files into printer cube files and offers three different print

modes (Solid, Strong and Sparse). The cube file contains all instructions to generate the tool

path of the deposition tip for the Cube machine. Once the cube file is imported into the Cube

via USB or wireless network, the front panel in the bottom of the Cube shows all instructions

34

in order to print the creation. The print jet print tip heats the thermoplastics at 280o C and

produces a thin flowing material of plastic creating 0.20 mm thickness of layers that adheres

to the print platform. After each layer is produced, the print platform lowers so that a new layer

can be drawn on top of the last. This process continues until the last layer on the top of the part

is jetted. Fig. 3.2 shows the schematic illustration of the FDM printing process.

Fig. 3.2. Schematic diagram of a Cube FDM Machine

3. 2.2 Part Fabrication by FDM

In this study, ‘dog-bone’ shape and flat shape samples were printed by Cube 3D machine to do

the numerous tests. In order to print ‘dog-bone’ shape specimen, typically ISO 527 and ASTM

D638 standards are followed by researcher to do tensile test for investigating the properties of

plastic materials. In order to be able to obtain significant results with the minimum number of

samples specimens, a design of experiments (DOE) was applied. The geometry of each

fabricated dog-bone shape sample was taken according to ASTM D638 to investigate tensile

Print Platform

Nozzle

Temperature Control Unit

Plastic Filament Cartridge

Roller

Fabricated Part

35

and fatigue properties in tension and size is 105 mm x 10 mm x 4 mm [72]. In order to do DMA

test, creep test, impact test and flexure test, several flat samples sized was 63 mm x 12.7 mm x

3 mm were printed according to ASTM D790. Fig. 3.3 shows the dimensions of the samples

used for this research, which could be fitted on the Cube 3D Printer. The 3D CAD model was

created using Creo Parametric software and then converted to a Stereolithography (STL) file.

The advantage of STL format is that the most CAD systems support it and it simplifies the part

geometry by reducing its basic components. The disadvantages of STL format is that it loses

some resolution which introduced acceptable by approximations [73]. To achieve the desired

sample, the chord height was set to 0 and angle control was set to 1 while saving as STL file

for the Cube software.

Typically, building a part using different print modes and different build directions will affect

the part strength and properties, so it is necessary to test in a variety of print orientations [14].

In this study, Solid print mode and three build orientations (X-, Y-, and 45o-) were used. Fig.

3.4 shows the three build orientations in the Cube software to make the PLA samples. Fig. 3.5

shows the deposited material build road pattern tool path for each of the three builds

orientations.

10 mm

4 mm 15 mm

20 mm

76 mm

50 mm105 mm135 mm

3 mm

63 mm

12.7 mm

a) b)

Fig. 3.3. Dimensions of the a) dog-bone shape and b) flat shape samples

36

3. 2.3 Part Fabrication by Injection Moulding

The test samples were fabricated from pellet form PLA material according to the

manufacturer’s product manual, using a Battenfeld BA 350/75 injection moulding (IM)

machine as shown in Fig 3.6. The pellets were injection moulded into standard rectangular

specimens according to ASTM D790 and tensile samples according to ASTM D638. The

temperature profile of injection from the feeding zone to the nozzle was controlled at

230/220/190/30°C and the measured injection pressure was1740 bar. Finally, the samples were

dried in a vacuum oven at 50°C.

b) Y-orientationa) X-orientation c) 45o-orientation

Fig. 3.5. Representative building layer styles of the samples

b) Y-orientation

X Y

a) X-orientation

X Y

c) 45o-orientation

X Y

Fig.3.4. Build orientations in Cube software

37

3.3 Test Methods

3. 3.1 Tensile Test

The tensile test of the PLA plastic material was conducted according to ASTM D638 using a

Zwick Z010 testing machine, which allows a maximum of 10 kN load and is controlled by

testXpert® II intelligent software. From the tensile testing results in stress-strain curve, one can

calculate ultimate strength, breaking strain and Young’s modulus which corresponds to a

polymers strength, ductility and stiffness respectively. The test was carried out at room

temperature and a strain rate of 50 mm/min. Wedge style cross-hatched grips were used for

proper griping of the specimens as shown in Fig. 3.7

Fig. 3.6. Battenfeld BA 350/75 injection moulding machine

38

3. 3.2 Fatigue Test

Fatigue tests are considered when parts are expected to perform under cyclic load applications.

In recent years, researchers have paid more attention on the fatigue behaviours of plastics as

plastics are increasingly being used in aerospace, automotive, biomedical and other leading

industries. Like all engineering materials, if plastic parts are considered under repetitive

loading then it is important to know the fatigue life of such parts. In general, thermoplastics are

more sensitive to various parameters and these parameters include stress or strain amplitude of

the loading cycle, mean stress, stress or strain rate, initial defects present in the component,

temperature, frequency and environment. These factors are to be considered when designing

the part for the fatigue life under cyclic loading and would provide a better understanding to

define materials to be used in specific applications.

Fig. 3.7. Specimen holding in a 10 kN Zwick machine

39

For fatigue testing, a Zwick Z010 universal testing machine was used, which allows a

maximum 10 KN load capacity. The machine was controlled by testXpert® II intelligent

software to control and record all test data. It was observed that a higher frequency increases

the body temperature of the sample, which results in decrease of fatigue life by enabling

material flow and increasing ductility, localized deformation at the weakest section of the

gauge length. Conversely, a lower frequency results in an increased fatigue life appearing

mostly in brittle fracture with limited deformation over the gauge length [74]. Therefore, the

tests were set at a frequency of 1 Hz at room temperature. No sample temperature control

device was supplied during the test due to the requirements defined for the test program. The

wedge style cross-hatched grips were used for proper griping of the samples as shown in Fig.

3.7.

In order to perform the fatigue tests, it was important to know the ultimate tensile strength

(UTS) of samples. So several number of trial run samples were tested under static loading, and

therefore, three close results were taken to determine the UTS for each orientation samples at

a strain rate of 50 mm/min. In the cyclic test program, the test parameters were kept unchanged

for each tested samples at various applied load conditions over the cycles. As the fatigue test

is a time consuming so one sample for each orientation was performed under cyclic load. To

set the number of cycles, three samples for the three different orientations were tested and then

set to 5000 cycles to overcome the data overflow in the test program. The applied load was

varied at 50%, 60%, 70% and 80% of UTS from sample to sample during testing. Due to time

consuming nature of cyclic loading experiment in a tensile tester, only one sample was tested

for each orientation and percentage of maximum load as the objective was to see the trend in

the fatigue behaviour of PLA parts in build orientations.

40

3.3.3 Flexure Test

In this study, the Zwick Z010 universal testing machine was used to perform flexure test of test

samples at a test speed of 10 mm/min. The selection type of testing was three-point bending

mode. According to ASTM D790, the support separation was at 40 mm, the tool separation at

start position at 6.5 mm and the preload was 5 N. The test program was controlled by

testXpert® II intelligent software which processed all data and evaluate all results in final form.

Fig 3.8 shows the three-point bending arrangement in a Zwick machine.

3.3.4 Impact Test

The experiments were carried out using a Ceast Instron Impact Tester. Notched samples for

impact tests were cut at the middle portion of the sample and were notched using a bench-top

notched machine. A minimum of 5 samples with notch length of 1 mm were tested for each

Fig. 3.8. Three point bending arrangement in a 10 kN Zwick machine

41

orientation and the results were averaged for each orientation samples. Fig. 3.9 and Fig. 3.10

shows the required testing arrangement for the Impact test.

3.3.5 DMA Test

Temperature ramp/single frequency is performed to determine storage modulus and loss

modulus and rest of all formulation by using a DMA 2980 dynamic mechanical analyser as

Fig. 3.9. Ceast Instron Impact test machine

Fig. 3.10. V-notched machine

42

shown Fig. 3.11 and tested in dual cantilever clamping mode at ramp rate 5 0C/min as shown

in Fig 3.12.

Fig. 3.11. DMA 2980 Dynamic Mechanical Analyser

Fig. 3.12. Dual cantilever arrangements in a DMA 2980 Dynamic Mechanical

43

The temperature was set to 30 0C to 110 0C. It works by supplying an oscillatory force, causing

a sinusoidal stress to be applied to the sample, which generates a sinusoidal strain. By

measuring both the amplitude of the deformation at the peak of the sine wave and the lag

between the stress and strain sine waves, quantities like the modulus, the viscosity, and the

damping can be calculated. A minimum of 7 samples of FDM PLA and injection moulded PLA

were tested and the results were compared.

3.3.6 Creep Test

Creep tests were conducted on a TA instrument Dynamic Mechanical Analyser. A tension type

clamp was used to evaluate the creep properties as shown in Fig. 3.13. Dimensions of sample

used in creep test were 63 mm in length, 12.70 mm in width and 3 mm in thick. Tensile stress

of 0.4 MPa was applied on each sample for two (2) hours which starts at room temperature

300C. A stress of 0.4 MPa was selected as it is the stress level at which PLA samples shows

linear viscoelastic properties. A total number of six (6) samples of FDM PLA were tested and

the average of each orientation samples was determined and was compared with the result of

injection moulded PLA samples.

Fig. 3.13. Specimen holding for creep test in a DMA 2980 machine

44

3.4 Summary

This chapter highlights the research specimens of PLA material which were processed through

FDM additive manufacturing process in three different build orientations and the test methods

to determine the effect of build orientations on its mechanical and viscoelastic properties. The

next chapter will develop and recommend information, appropriate for the design engineer,

about FDM PLA material and it also leads to a comparison with the injection moulded

materials.

45

CHAPTER 4

Mechanical Properties of FDM PLA Thermoplastic

4.1 Introduction

In this chapter, FDM processed PLA specimens under different build orientations were tested

and analysed to determine which orientations have most impact on maximising the mechanical

properties of PLA. The mechanical properties include tensile, flexural, fatigue strengths and

impact energy of PLA thermoplastic in three build orientations. Then, these results were

compared with the injection moulded (IM) parts which provides knowledge for design

engineers about the suitable application of FDM PLA parts in industrial use.

4.2 Tensile properties

In this study, three build orientations were considered and for each build orientation, and in

each case, three specimens were tested to obtain average results [21]. Therefore, a total of nine

specimens were tested for three build orientations. Although the specimens’ surface finishing

in two build orientations (X -and 45o-) were found to be good, the specimens printed in Y-

orientations resulted in uneven surface. The output file of tensile tester was converted into

tensile stress and strain graphs by using Matlab script. Fig. 4.1 shows the average stress-strain

graphs obtained from tested specimen, and also shows the comparison of the average stress-

strain curves of the FDM specimens in three build directions and IM specimens. From the

graphs, the modulus of elasticity for each PLA sample was calculated by plotting the slope in

its elastic region. The resultant tensile properties have been published in [80]. Table 4.1 shows

the average values and standard deviations of tensile stress, tensile elongation and modulus of

elasticity for three different build orientations.

46

Table 4.1- Tensile Properties of the FDM and IM specimens

Build Direction

Tensile stress (MPa)

Tensile Elongation (%)

Tensile Modulus (MPa)

Average Standard

deviation

Average Standard

deviation

Average Standard

deviation

FDM-X 38.65 0.14 4.14 0.08 1538 2.38

FDM-Y 31.43 0.33 4.53 0.12 1246 3.74

FDM-45o 33.63 0.70 4.45 0.20 1350 1.47

IM 31.4 1.32 3.6 0.28 1223 2.48

From the results shown in Fig. 4.1 and Table 4.1, it can be observed that the X-build orientation

shows the highest tensile stress of 38.7 MPa and the highest tensile modulus of 1535 MPa

compared to the Y- and 45o- build orientations and IM specimens. This is due to the fact that

the tool path beads in the X-orientation are laid parallel to the length of the tensile sample and

offer greater resistance to fracture. The specimens in Y and 45o orientations show slightly better

ductility (tensile elongation and mention other indicators). The published value of tensile stress

Fig. 4.1. Average stress vs. strain graph of different orientations FDM specimens and IM specimens

47

based on ASTM D638 standard for generic PLA material ranges from 61 to 66 MPa [75].

Hence, the PLA parts produced by FDM possess around 60 to 64% of tensile stress of the raw

PLA material. Fig. 4.2 shows the images of specimens in X-, Y- and 45o-orientations after the

completion of the tests.

Also, it was noted from Fig. 4.2 that the fracture in specimens mostly occurred nearer the neck

of the specimens built in X- and Y-orientations, but in 45-orienation specimens, it occurred

near the middle section of the specimens built. This could be attributed to the tool path layout

patterns in the specimens built in these orientations for FDM technology. Fig 4.3 shows an

overview of IM specimen.

Fig. 4.2. Tested PLA specimens in different build orientations: (a) X-orientation,

(b) Y-orientation and (c) 45o-orientation

(c)

(b) (a)

(a) (b) Fig. 4.3. Overview of an IM specimen: a) before test and b) after test

48

4.3 Fatigue Properties

In this study, the same ‘dog-bone’ specimens as used in tensile test according to same standard

were used to investigate fatigue strength at 80, 60, 70 and 50 percent of their respective ultimate

tensile strength [15]. All specimens were subjected to uniaxial tension while conducting static

and fatigue tests. The pull-out and retraction were controlled within its maximum and minimum

load for each specimen. Tensile tests were conducted for five samples for each build orientation

with a single pull until failure to determine ultimate tensile stresses and to verify tensile results.

However, the ultimate tensile stresses of the FDM specimens for the three different orientations

were found to be different since it depended on build orientation styles (solid, strong and

sparse) and orientations, rather than the material itself. Though the tensile strength of the raw

material was more consistent and higher than the FDM specimens, it was observed that the

tensile stress was around 60 to 64% of the generic raw PLA materials [75]. The output excel

file of tensile tester consisted of four columns representing maximum stress (MPa), elongation

at maximum stress (mm), stress at break (MPa) and elongation at break (mm) respectively.

The data were post-processed into stress, strain and number of cycles using Matlab script. The

results of fatigue tests have been published in [81]. Fig. 4.4 shows the typical pull history while

cyclically loading at 50% of UTS for the specimens of three orientations named PLA-X, PLA-

Y and PLA-45o respectively. Table 4.2 shows the average values of UTS and average values

of modulus of elasticity obtained by static testing and the amount of applied load at 80%, 70%,

60% and 50% of UTS used during fatigue testing for each of these three orientations.

49

Table 4.2: Data outlining the average ultimate tensile stress (σu), average modulus of

elasticity and applied load in percentage of UTS

Orientation of Specimen

Ultimate Tensile Stress (UTS)

σu (MPa)

(Table 4.1)

Modulus of

Elasticity

(MPa)

(Table 4.1)

Applied load (%UTS)

(MPa)

80% 70% 60% 50%

PLA-X 38.7 1538 30.96 27.09 23.22 19.35

PLA-Y 31.1 1246 24.88 21.77 18.66 15.55

PLA-45o 33.6 1350 26.88 23.52 20.16 16.8

0 1 2 3 40

5

10

15

20

Strain (%)

Stre

ss (M

Pa)

a) X-orientation

0 1 2 30

5

10

15

Strain (%)

Stre

ss (M

Pa)

b) Y-orientation

0 1 2 3 40

5

10

15

20

Strain (%)

Stre

ss (M

Pa)

c) 45o- orientation

Fig. 4.4. PLA specimens showing the pull history at 50% of the ultimate tensile stress

50

Generally, parts fail in high stress concentration areas under cyclic loading applications. For

homogeneous parts, a failure should appear directly in the middle of the part. Fig. 4.5 shows

the failure profile of tested specimens for three build orientations according to 50%, 60%, 70%

and 80% of their UTS respectively. The failure profile of the specimens appears in different

locations due to the different build style road pattern in each build orientations, which affect

the material properties. From Fig.4.5, it can be seen that the fatigue failure location for the X-

orientation specimens appeared consistently at the same location across the neck as the build

pattern roads are along the length of the tensile sample. In the Y- and 45o -orientations

specimens, the build pattern roads were either perpendicular or at 45o to the length of the

sample, and this resulted in failure at different locations where the parts were highly stressed.

It is noted that at 50% of UTS, the specimen in Y-orientation has lower applied tensile stress

than X- and 45o-orientations, but it has displayed better ductility as the failure occurs middle

of the specimen as compared to two other orientations (See Table 4.2 and Fig. 4.5). Note that

from stress-strain graphs, the modulus of elasticity of PLA for three distinct orientations were

calculated by plotting slope on its elastic region while specimens were tested to determine the

UTS for each orientation.

a) X-orientation b) Y-orientation

c) 45o-orientation Fig. 4.5. Images of fatigue tested specimens at their 50%, 60%, 70% and 80% of UTS

respectively

51

Because of the sensitivity in many factors, the fatigue test conditions must closely mimic the

service conditions of the thermoplastic part and the S-N approach is widely accepted in the

engineering community for design applications when considering cyclic loading. Fig.4.6 shows

the stress vs. numbers of cycles to failure curves (S-N curves) for X-, Y- and 45o-orientations

specimens subjected to static stress at their 50%, 60%, 70% and 80% of UTS. Despite the

inevitable scatter, the pattern of behaviour appears to be similar for all three build orientation

parts and each point shows the failure point of each specimen when they are cyclically loaded

at a certain percentage of their UTS value. Note that the average values of UTS for X-, Y- and

45o -orientation specimens were 38.7 MPa, 31.1 MPa and 33.6 MPa respectively as in Table

4.2. From Fig. 4.6, it can be seen that although the X-orientation specimens experienced highest

UTS, it generated lower fatigue life cycle than other two orientation specimens. However, the

specimen in 45o-orientation had a lower UTS than the X- orientation specimen, but it showed

a higher number of fatigue life cycles than X- and Y-orientation specimens. This trend is due

to build orientations of printed specimens and build pattern road in relation to build direction.

It was observed that for 45o-orientation specimen at approximately 50% of UTS, the number

of cycles is roughly 1380 until its failure.

100 102 1040

10

20

30

40

Number of Cycles (N)

Stre

ss (M

Pa)

PLA-XPLA-YPLA-45

Fig. 4.6. S-N curves for three (X, Y and 45o) orientation samples

52

The area under the stress-strain curve is the modulus of toughness or total strain energy per

unit volume consumed by the material until failure. The strain energy can be calculated by

using the following formula [76].

Total Strain Energy (𝑈) = ∫ 𝜎 𝑑 ∈∈

0 (1)

where 𝜎 is the stress and ∈ is the strain.

Therefore, if the stress-strain curve is integrated numerically, the total strain energy can easily

be calculated. In this study, the total strain energy was calculated by using a Matlab function

“trapz” which numerically calculates the total area under the stress-strain curve, i.e., the total

strain energy. Fig. 4.7 shows the strain energy vs. cyclic load for 50%, 60%, 70% and 80% of

UTS for specimens in all three build orientations. From Fig. 4.7, it can be observed that the

45o-orientation specimen experienced higher strain energy as compared to other build

orientations with a value of 2048.9 kJ m-3 until it failed at 1380 cycles. On the other hand, the

specimens in X- and Y- orientations experienced strain energy of 466.69 kJ m-3 and 1421.69

kJ m-3 respectively, and the numbers of cycle until failure for X- and Y-orientations were 175

and 708, respectively. These three trends were consistently presented for all other tested

specimens subjected to loading of 60%, 70% and 80% of UTS.

Typically, the strain energy decreases while testing at higher tensile stress. From Fig. 4.7, it

can be observed that the specimen in 45o-orientation experienced highest strain energy with

respect to the percentage of cyclic loading conditions from other orientations. Thus, this study

reveals that the PLA specimens printed in 45o-orientations have higher modulus of toughness,

absorb more energy and last longer till failure under fatigue loading conditions compared to

the PLA specimens built in the X- and Y-orientations specimens. This aspect is to be

considered when designing FDM built parts for cyclic loading applications.

53

4.4 Impact Properties

The impact test measures the impact resistance of thermoplastics. The energy absorbed by the

tested part is the difference in potential energy of the hammer before and after the impact [77].

Each specimen with dimension (63 mm x 12.7 mm x 3) mm were notched before impact testing.

In this test, 5 FDM specimens in three (X-, Y- and 45o-) orientations and 4 injection moulded

(IM) specimens were tested, and from these, 3 tested specimens were taken to obtain an average

result for the FDM and IM specimens. All data were processed by the CeastVIEW software

and collected in an excel file to plot the graphs. Table 4.3 shows the average results from impact

tests. Due to small size of the specimens, it was noted that the surface finish was good in each

orientation and the impact test results were different for each orientation. Fig. 4.8 shows the

overview of tested specimens and Fig. 4.9 shows the impact energy absorbed by the specimens

and resilience. The resilience is the energy absorbed by the area so it can be calculated by the

formula

Resilience = Impact Energy

Notched Area (2)

50 60 70 800

500

1000

1500

2000

2500

Cyclic Load (% of UTS)

Stra

in E

nerg

y (k

J/m

3)

PLA-XPLA-YPLA-45

Fig. 4.7. Strain energy vs. percentage of UTS for specimens in different (X, Y and 45o) orientations

54

Specimens Impact Energy

(J)

Resilience

(kJ/m2)

FDM-X 0.15 4.80

FDM-Y 0.11 3.36

FDM-45o 0.14 4.35

IM 0.15 4.54

It was observed that the specimens in X- orientation have the higher impact energy as well as

higher impact resistance than specimens in Y- and 45o- orientations. The average values of

impact energy and energy absorbed over the area, that is resilience for X- orientation

specimens, were 0.155 J and 4.80 kJ/m2 which was greater than average value of IM specimens

result. On the other hand, the resultant value in Y- and 45o- orientations specimens were less

Table 4.3- Average impact energy and resilience of the FDM and IM specimens

a) FDM-X b) FDM-Y

c) FDM-450 d) FDM-IM

Fig. 4.8. Images of impact tested specimens

55

than the value of IM specimen. From the analysis, the X-orientation specimens experienced

good ductility than the Y- and 45o- orientations specimen

4.5 Flexural Properties

Flexural test was completed at room temperature via a Zwick Z010 universal testing machine.

Flexural testing was conducted according to ASTM D790 and the testXpert® II intelligent

software run the tester and finally evaluated the results. All data shown was taken from FDM

processed specimens in three different orientations and injection moulded specimens. Each

orientation had five specimens that were tested and from these tested result, three required

closer data were processed. Figure 4.9 shows all resultant data that were plotted in flexural

strength (MPa) vs. deformation (%). The flexural strength was maximum for FDM processed

specimens in the case of 450 build orientation as shown in Figure. 4.9 and Table 4.4. In Table

4.4 , although the standard deviation in the case of 450 build orientation specimens were higher

than the other two build orientations specimens and IM specimens, the resultant average values

of all FDM processed PLA specimens in three build orientations were similar, and higher than

the injection moulded (IM) specimens. The maximum flexural strength was 84.71 MPa at 4.84

percentage of deformation for FDM processed in 450 build orientation.

Fig.4.9. Average flexural strength vs. deformation curve for FDM and Injection moulded specimens.

56

Table 4.4 Flexural Properties of the FDM and IM specimens

Specimens Maximum Flexural Strength (MPa)

Deformation at maximum flexural

strength (%)

Flexural Modulus (MPa)

Average Standard deviation

Average Standard deviation

Average Standard deviation

FDM-X 82.57 1.29 4.54 0.20 2480 1.41

FDM-Y 83.08 2.73 4.20 0.08 2479 0.82

FDM-45o 84.71 5.97 4.84 0.32 2485 2.94

IM 53.48 2.85 3.18 1.15 2253 2.16

b) a)

c) d)

Fig.4.10. Specimens after testing

57

From the experiments, it was noticed that all FDM specimens did not break after testing, but

in case of IM specimens, most of the specimens experienced breakage into two parts (See

Figure. 4.10). Therefore, the injection moulded specimens showed lower ductility than the

FDM processed specimens.

4.6 Summary

From all completed tests, the FDM processed PLA materials showed much more favourable

qualities in terms of their orientations. It was clear that PLA processed through FDM method

has some desirable properties in regard to mechanical properties. Though it was experienced

that the specimens in X build orientation have higher ultimate tensile strength and higher

percentage elongation at failure than Y and 450 build orientations. However, for fatigue testing,

it is possible to say specimens of 450 build orientation last longer (higher number of cycles)

before they fail. Also, the impact energy and the flexural strength were higher in the 450 build

orientation than X and Y. It was also noticed that the impact and flexural properties were better

than the injection moulded specimens. The next chapter covers the viscoelastic properties of

FDM processed PLA specimens and injection moulded specimens as a comparison.

58

CHAPTER 5

Viscoelastic Properties of FDM PLA Thermoplastic

5.1 Introduction

Fused Deposition Modelling (FDM) has achieved its popularity as compared to conventional

machining due to its low cost and require shorter time while rapidly fabricating real parts from

Computer Aided Design (CAD) data. This chapter sheds light on the effect of build orientations

on viscoelastic properties as well as the dynamic mechanical properties and creep properties of

Polylactic acid (PLA) material that fabricated by FDM additive manufacturing process. The

considered build orientations are in the X, Y and 450 directions. The dynamic mechanical

analysis (DMA) and creep analysis were carried out by a TA Instrument DMA 2980 machine.

The experimental results from the tests were evaluated and compared with the Injection

Moulding (IM) samples results to analyse the effects of build orientations on its dynamic

mechanical and creep properties. Figure 5.1 shows an overview of FDM and IM sample.

5.2 DMA Properties

Dynamic mechanical analysis experiments were carried out for FDM fabricated and IM

fabricated samples. All rectangular samples were tested by a TA Instrument DMA 2980

machine which allows various shape of geometries to fit in its clamping system. It offers

(a) (b)

Fig. 5.1. Sample for DMA and creep test: a) FDM sample and b) IM sample

59

various clamping modes including single/dual cantilever, three-point bend, shear sandwich,

compression and tension modes. Typically, DMA can sweep over frequency or temperature

range. In this study, the dual cantilever clamping mode and temperature sweep of DMA 2980

were employed to do all tests. For DMA experiments, all samples were tested using the

temperature ramp/single frequency method at ramp rate 5 0C/min, and the temperature ranged

from 30 0C to 140 0C according to the melting point of PLA material. The frequency scan was

done at three different temperatures for all samples. For all PLA samples the chosen

temperatures were 40 0C, 60 0C and 70 0C. After all experiments were completed, the

experimental results were evaluated by the Thermal Advantage software. Thermal Advantage

software is a Universal Analysis software which offers a great convenience for users to plot

custom graphs [23]. This software stored all value of storage modulus, loss modulus, tan delta

and complex viscosity across temperatures after completing tests. All necessary data were

collected for post-processing and finally plotted all graphs and bar charts in Matlab. The

temperature is set in the X-axis as it was the temperature sweep method, while storage modulus,

loss modulus, tan delta and complex viscosity were set in the Y-axis. Three different types of

Fig. 5.2. Temperature scan graph of loss modulus and tan delta of PLA FDM and IM samples

60

data were plotted in an overlapping manner. Figure 5.2 shows loss modulus (LM) and tan delta

(TD) of FDM and IM samples against the variation of temperature. From Figure 5.2, it can be

seen that the nature of loss modulus and tan delta is quite similar though their values are

different. The values of glass transition temperatures were taken out from the peak of tan delta

curves corresponding to the temperatures.

Similarly, Fig 5.3 shows such overlaid graph of storage modulus (SM) and complex viscosity

(CV) of FDM samples in three build orientations and IM samples. In Fig. 5.2 to 5.3, in all

cases, the values of loss modulus increases with the increase of temperature and the values of

storage modulus decreases with the increase of temperature at constant frequency. This is due

to the relaxation in the polymer chain because in polymers, the tendency to store energy

decreases with the increase in temperature and the tendency of loss energy increases with the

increase in temperature. The reductions in storage modulus and the glass transition temperature

are typical consequences [78]. As it is a temperature sweep method, from the graphs the

maximum property values of FDM and IM samples are taken at 40 0C, 60 0C and 70 0C

Fig. 5.3. Temperature scan graph of storage modulus and complex modulus of PLA FDM and IM samples

61

temperature and shown in Table 5.1. These values were selected to investigate the effects of

orientations in case of FDM samples and to compare with the IM samples.

Table 5.1. Property values of FDM and IM samples for solid normal build style

Samples Temper-ature (0C)

Max storage

modulus (MPa)

Max loss modulus (MPa)

Peak of tan delta

Tg (0C)

Max complex modulus (MPa)

Max complex viscosity

(MPa*sec)

PLA-X

40 60 70

1286 1060 68.84

24.32 143

100.29

1.46 75 1286.23 1069.60 121.63

204.81 170.32 19.37

PLA-Y

40 60 70

1431 1212.5 90.14

24.91 132.18 132.33

1.50 70

1431.22 1219.68 160.11

227.9 194.17 25.50

PLA-450

40 60 70

1300 1042.55 73.40

21.74 133.13 101.92

1.44 70 1300.18 1051.02 125.60

207.04 167.36

20

PLA-IM 40 60 70

2024 1612 97.57

60.8 130.9 101.7

1.04 70 2024.91 1617.31 140.94

322.44 257.53 22.44

As all property values were obtained from the experimental runs, some property values like

storage modulus, loss modulus and tan delta were collected and compared in bar charts. Figure

5.4 shows such charts plotted with temperature in the X axis and maximum storage modulus

values in the Y axis. These maximum values were obtained against temperatures for three

different orientations. This figure shows clearly the decrease in storage modulus with increase

in the temperature. This phenomena is due to the relaxation in polymer chain and such

relaxations with a large tan delta peak are responsible for the greater strength of the material

[79]. The values of storage modulus of FDM and IM samples are higher at 40 0C temperature

and deceases gradually with increase in temperature. From the Table 5.1 and Figure 5.4, it can

be seen that the value of storage modulus is higher for IM samples and then for Y build

62

orientation. The sample build in Y orientations obtained highest value of 1431 MPa, then X

and 450 build orientations, and attained around 71% strength (SM) of IM material when

subjected to single frequency/ temperature ramp method. It can be concluded that the parts in

Y build orientations have the greater toughness as compared to other two build orientations.

Figure 5.5 shows the effects of temperature on loss modulus properties. Loss modulus is the

tendency to loss energy of the material which is opposite of storage modulus. Typically loss

Fig 5.4. Effect of temperature on storage modulus properties

Fig 5.5. Effects of temperature on loss modulus properties

63

modulus increases with increase in temperature. But from this figure, it is clearly noted that

loss modulus of all FDM and IM samples have higher values at 60 0C temperature, and samples

made in X build orientation have high loss modulus value of 143 MPa, which is greater than

the IM samples. At 70 0C temperature, the values of loss modulus have decreased due to

transition of the material. Therefore, parts made in the X- build orientation is stronger than

other two build orientations.

The graph between tan delta and temperature is shown in Figure 5.6. Typically, tan delta is

directly proportional to loss modulus. Therefore, if the loss modulus increases with the

temperature, then the tan delta also increases. As mentioned earlier, the peaks of tan delta

increase with increase in temperatures and at the higher temperatures, the molecular energy

dispersion mechanism operates which indicates toughness of the material. From the Figure 5.6,

it can be seen the peak of tan delta is higher for Y build orientation samples than others. When

compared with other samples values including X build orientation, 45 build orientation and IM

samples, the values of peak tan delta are close enough for FDM samples and even better than

IM samples. Therefore, parts built in the Y orientation have the highest tan delta peak which

means the material is tougher.

.

Fig 5.6. Effect of temperature on tan delta properties

64

Figure 5.7 shows the complex modulus plot as a function of temperature. Typically, the

complex modulus is nearly equivalent to storage modulus. Figure 5.6 provides the effect of

temperature on complex modulus and glass transition temperature. It can be seen that at 40 0C

the complex modulus of FDM and IM samples are higher and gradually decreases at 60 0C and

then at 70 0C temperature. Among the three different build orientations samples, the samples

made in Y build orientation have experienced high complex modulus value of 1431.22, which

is about 71% complex modulus value attained by IM samples than X- and 45- build orientations

samples.

Figure 5.8 shows the results complex viscosity properties when subjected to temperature sweep

method. The complex viscosity property values of FDM and IM tested samples are shown on

the complex viscosity curves at temperature of 40 0C, 60 0C and 70 0C. Typically, Newtonian

fluids such as liquids and oils exhibit viscous behaviour. But in case of a material when

subjected to applied stress, and resulting strain is not recoverable, that increases proportionally

with time until the stress is removed. Thus, some energy losses in the system and materials

exhibits some viscous properties. In the case of PLA thermoplastic, the complex viscosity

Fig 5.7. Effect of temperature on complex modulus properties

65

decreases with increase in the temperature, and the sample made in Y build orientations possess

higher value when compared to other two build orientations samples.

5.3 Creep Properties

The experiments to evaluate creep properties were carried out by DMA 2980 for all FDM and

IM samples. In this study, a tension film type clamp was engaged to hold the samples. The

rectangular samples sized (63 mm x 12.7 mm x 3 mm) according to ASTM D790 were tested

for creep at isothermal 30 0C. A constant stress 0.4 MPa was applied resulting in strain for 120

mins duration. Once all experiments were done by DMA 2980, the resulting data were stored

automatically in Thermal Advantage software. All data was stored as strain and creep

compliance over time, and were post processed to plot graphs. The values of strain and creep

compliance were plotted in the Y axis and time was plotted in the X axis. These experiments

show obvious differences between these samples. Such graph showing the effects of strain over

time are in Figure 5.9.

Fig 5.8 Effect of temperature on complex viscosity properties

66

The assumption is that the higher value of strain of the material indicates a greater strength of

the material. However, the percentage strain of Y-build orientation sample is lower than IM

sample but greater than X- and 45o- build orientations samples as shown in Figure 5.9. Among

three build orientations samples, it is clearly seen that the curve of 45o-build orientation sample

is lower than the X- build orientation sample, which is less than Y-build orientation sample.

Figure 5.10 shows a plot of creep compliance Vs time graph. Typically, creep compliance is

the inverse of modulus for an elastic material which is the willingness of the material to deform

[66]. Similar curves are shown in Figure 5.10 where samples made in build orientations X and

Y have progressively a higher value of compliance than 45o- build orientation sample.

Fig 5.9. Plot of percent strain against time

67

Fig 5.10. Plot of creep compliance against time

5.4. Summary

This chapter has focussed on the effects of build orientations on dynamic mechanical properties

and creep properties of PLA samples processed through FDM technology. The DMA

experiments were carried out according to temperature sweep method at constant frequency

and the properties were investigated at three different temperatures. Result have shown that the

loss modulus increases with increase in temperature, but the storage modulus and complex

viscosity decrease with decrease in temperature. From the results of the dynamic mechanical

properties of FDM samples, it can be seen samples made in Y-build orientation gives best

values compared to X- and 45o- build orientations samples and achieved around 71% strength

of the IM parts. The samples made in Y- build orientation have more strength. Similarly, creep

test samples made in Y- build orientation have more strength than other two build orientations

samples. This understanding will help in the material selection process and assist design

engineers to optimize the cost of the PLA material. Therefore, the Y- build orientation is

considered best choice for design engineers when PLA materials parts are fabricated through

FDM technique

68

CHAPTER 6

Conclusion and Further Research

6.1 Overview

Polylactic acid (PLA), made from renewable sources is a compostable as well as a

biodegradable thermoplastic polymer. As it is environment friendly and cheaper than

petroleum based polymers, it became popular for producing consumer products. Now

researchers have considered PLA to use in building, agriculture, transportations, electrical

appliances and houseware. Therefore, the study of PLA properties becomes an important issue

now-a-days. Current industrial processing practices based on melt-flow techniques are time

consuming and costly. To overcome such difficulties fused deposition method (FDM), which

is a rapid prototyping process, has extensively been used to produce such industrial purpose

physical objects from computer aided data (CAD) with a shorter time. Therefore, the thesis

was focused to investigate as well as analyse the effects of different FDM build parameters on

PLA properties and find out the best build parameter in which processed PLA parts shows best

properties. In this chapter, the resulting effects of three different build orientations are

summarised to analyse the properties of different PLA parts which are processed through FDM

technique and further research in this area has been discussed.

6.2 Conclusions

The literature review showed that the FDM techniques and thermoplastic polymers that are

processed through FDM have been studied. However, it was found that the properties of PLA

had not previously been investigated through the FDM process. Hence, this study involved a

Cube 3D FDM machine to fabricate samples and investigation of the build parameters on

69

material properties during fabrications. In this study, the injection moulded samples were

prepared and tested in order to compare with the FDM sample results.

First the samples were fabricated according to ASTM D 638 and ASTM D 790 by a Cube 3D

printer machine by using X-, Y- and 450-build orientations and solid normal build style was

used as it was experienced that Solid normal build style gives best properties during

fabrications through FDM. Also, a number of samples were fabricated to compare with the

FDM results by using a Battenfeld BA 350/75 injection moulding (IM) machine. The FDM

and IM samples were tested for tensile, fatigue, impact, flexural, dynamic mechanical analysis

and creep properties.

The second study attempted to characterize the mechanical properties and viscoelastic

properties of tested samples. The build orientations have a great influence on the PLA samples.

For tensile loading applications, it was experienced that material parts should be fabricated in

X- build orientation as it showed higher tensile strength and tensile modulus than Y- , 450-build

orientations and IM samples. It was observed that for samples made in 45o- build orientation

last longer under cyclic loading conditions until its failure than X- and Y-orientations samples

and have highest number of cycles such as for 50% of UTS, the number of cycles is roughly

1380 until its failure. In case of impact test, the samples made in X- orientation have the higher

impact energy as well as higher impact resistance than samples made in Y- and 45o-

orientations. However, the values of the maximum flexural strength were close enough among

in the three build orientations samples, but it was found slightly higher maximum flexural

strength as well as the flexural modulus in case of 450 build orientation samples.

For dynamic mechanical analysis (DMA) experiments, the results showed that the properties

such as storage modulus, complex modulus and complex viscosity were decreased with an

increase in temperature. On the other hand, the properties like loss modulus and tan delta were

increased with an increase in temperature. The samples made in Y- build orientation showed

70

higher values of storage modulus, complex modulus and complex viscosity than samples made

in other two build orientations and attained around 71% strength of IM material samples.

However, the value of loss modulus was higher in X- build orientations samples, but in case of

tan delta property, it was observed that samples made in Y- build orientation attained higher

values of tan delta than samples made in X- and 450 build orientations. For creep test, the results

obtained from the experiments showed that the greater value of strain as well as the creep

compliance for Y-build orientation samples increase the strength of the PLA material, thus

increasing the flowability of the material. So parts should be fabricated in Y- build orientation

while performing long term loading applications as the Y- build orientation samples have

higher creep properties than other two build orientations.

In conclusion, this understanding will improve the material selection process and assist in

optimizing the cost/ performance balance to the design engineers. The research activities

presented in this thesis will also assist the designers for developing guidelines where FDM built

parts are applicable in different orientations as well as in different loading conditions.

6.3 Further Research

Further recommended work in the area of analysing material properties as presented in this

thesis will include:

Compression test in different build orientations, which is required when parts are under

compression loading applications.

Compressive and flexural fatigue testing which enable to gather more knowledge on

fatigue behaviours of different parts processed through FDM.

The investigation of thermal properties in different build orientations, which may be

the required criteria for some of the applications.

71

Creep recovery and stress relaxation tests, which includes viscoelastic behaviours of

FDM processed parts.

Such investigations would be extremely useful to help design parts as more and more additive

manufactured parts and materials are being applied to various engineering applications in

different loading conditions.

72

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