Numerical Study of Tensile Properties of POM/Woven Kenaf Composite

By

Muhammad Syahir Bin Shaiful Haslan15151

Interim Report Bachelor of Engineering (Hons)(Mechanical Engineering)

JANUARY 2014

Universiti Teknologi PETRONASBandar Seri Iskandar 31750 TronohPerak Darul Ridzuan

ABSTRACT

Woven fibers are considered to be useful as a reinforcing material within composites. They provide many advantages in the application of polymer matrix composites by increasing the transverse strength and stiffness. In order to fully realize the potential of woven fiber reinforced composite, it is imperative to understand the mechanical behavior of the composite. In this study, predications of tensile properties of woven fiber composites are proposed using a numerical methods. However, this study has some challenge as there is a very limited paper focusing on prediction of tensile properties of woven fiber composite. The tensile properties of POM/woven kenaf laminate composite are determined with assumption that classical laminate theory is applicable. The continuous fiber will be stacked as plies in a laminate with different orientation so that the laminate properties will represent the equivalent properties of woven fiber. The fiber architecture, including the fiber waviness is properly accounted for. The results obtained from the study will then be used to compare and validate through experiment done by another researcher.

CHAPTER 1INTRODUCTIONThe aim of this chapter is to introduce the basic and general overview of the project which are background study, problem statement, objectives and scope of study.1.1Background StudyFiber reinforced composite is one of the advanced technologies that has been expanding in the engineering material industry. Many studies have been conducted to investigate the tensile properties of biodegradable composite materials using natural fibers as a reinforcement for the polymers [1].There is a growing interest in the use of woven composite for various type of applications. Such applications range from bio-medical components, aircraft and space structures to automotive and other applications. However the geometry of woven fiber reinforced polymer like (POM) and woven kenaf composite is quite complex. Numerical method is required to predict tensile properties of such composite. With the development of the computing capabilities, numerical methods are more favorable compared to analytical and experimental methods. This is because analytical methods are difficult to apply on complex model meanwhile experimental work is time and cost consuming. Therefore, a successful implementation of this numerical study will allow the tensile properties analysis to be conducted thoroughly without being too dependent on experimental and analytical methods. By understanding the classical lamination plate theory and the stress-strain relationships, the numerical arrangement of the stress and strain values for the angle-ply symmetric laminated plates for various lamination angles can be carry out [2]. The classical lamination plate theory is based on the love-kirchhoff theory with a few hypothesis made.

1.2Problem StatementExperimental study of tensile properties on polymer/woven fiber composite was done by Yakubu [3] and other researchers [1, 4]. However effort on predicting tensile properties of woven fiber reinforced polymer is very limited. Therefore, this project is proposed to predict the tensile properties of POM/woven kenaf laminate composite by using numerical analysis.

1.3ObjectivesThe objectives of this project are:1. To predict tensile strength and modulus of POM/woven kenaf composite using numerical method.2. To validate the numerical data with existing experimental results.

1.4Scope of StudyIn this study, POM will be used as the matrix and kenaf will be employed as the reinforcement. The mechanical properties of POM and kenaf fiber will be extracted from POM technical data sheet and published journal paper, respectively. POM FM090 grade and kenaf yarn imported from Bangladesh will be used in this project. The composition of POM/woven kenaf that will be used in this project are 80/20 and 70/30 wt %. To calculate laminate material properties and ply stiffness, Laminator software will be used. A micromechanics calculator which is also included in the software will be used to estimate lamina properties for given fiber and matrix properties.

CHAPTER 2LITERATURE REVIEWFiber reinforced composite materials offer outstanding mechanical properties, ease of fabrication and unique in design capabilities. A growing interest in woven composites has been observed in recent years. A woven fibers oriented on at least two axes in order to provide great strength and stiffness [4]. This chapter describes the theory used in understanding laminate composite structure. Special emphasis is given to the woven fiber composite as it plays an important role on the mechanical properties of the composite.2.1Classical Lamination TheoryA laminate is an organized stack of uni-directional composite plies (single fiber direction rather than a weave pattern) [5]. By stacking layers of different composite materials and/ or changing the fiber orientation, one can form composite laminates. The most known theory for calculating laminated structures is the Classical Lamination Theory.This theory enables analytical stress-strain analysis of the laminated structures when being subjected to either mechanical or thermal load. Arbitrary number of layers, layer thicknesses and material type (isotropic, anisotropic) can be taken into account. This enables us to calculate stresses and strains for each layers, laminate properties or total deformation of the laminate. These laminate properties are then used as the materials data in a structural analysis, where the influence of structure geometry and loads are calculated and structural failure criteria applied [6]. The stacking of the material is defined by the fiber directions of each ply. Figure 2.1 shows the example of different laminate stacking sequences.

Figure 2.1: Example laminate stacking sequences [5].In addition to the stacking sequence, the material properties of the composite material must be defined:i. Mechanical Elasticity ().ii. Thermal Expansion ().

2.2Equation for Ply PropertiesUsing the rule of mixtures, we can derived the equation to calculate the ply properties. The equations for calculating ply properties are shown below [6, 7].

I. Modulus of Elasticity in the longitudinal direction: (1)

II. Modulus of Elasticity in the transverse direction:(2)

III. Shear modulus of ply: (3)

IV. Poissons ratio: (4)

V. Density of the composite: (5)

VI. Shear Stress: (6)

VII. Longitudinal Coefficient of Thermal Expansion: (7)

VIII. Transverse Coefficient of Thermal Expansion: (8)

2.3Woven Fiber CompositeThe demand for woven fiber composite is increasing tremendously due to simple processing technique, acceptable mechanical and physical properties and lower cost of production [8]. Woven composites provide more balanced properties in the fabric plane than unidirectional laminas. Woven fiber composites, in particular are constructed by weaving two fiber tows into each other to form a layer. Figure 2.2 shows some examples of weaves used on most fibers.

Figure 2.2: Basic weaves used on most fibers [9].According to Rahul Garg et al. [10], the simplest and common type of weave that inexpensive to produce, durable, flat and tight surface is plain weave. Each weft yarn goes alternately under one warp yarn. The interlacing pattern of the warp and fills known as the weave [11]. Figure 2.3 shows the example of plain weave structure.

Figure 2.3: Plain weave structure.There are only few reports on woven fiber composites reported so far. According to Mithat Zeydan et al. [12], parallel yarns in woven fabric are only contact with each other over a fraction of their length. Hence to produce an analytical model, a number of simplifications are required. However, the methods is extremely time consuming, very tedious and cannot be used in a routine manner for woven composite [13]. Such analytical methods should only be used at structural level or strictly at the micromechanical level. Therefore, using the capabilities that already exist for laminated composites but yet account the fiber woven using different orientation of the laminate, woven composite behavior will be simulated.Because of the thickness of the fiber is small, the woven fiber can be regarded as a thin lamina [11]. To simulate woven fiber, the continuous fiber will be stacked as plies in a laminate with different orientation (0/90) and the laminate properties will represent the equivalent properties of woven fiber. These layers are then impregnated with resin or matrix material, stacked in a desired orientation and cured to obtain a composite laminate [13]. Figure 2.4 shows the arrangement of laminate with two different orientations. The 90 ply in the laminate represents the fill yarn while 0 ply represents the warp yarn.

Figure 2.4: 2-ply laminate stacked with different orientation (0/90).

A conventional (0/90) laminate fabricated from the same material, graphite/epoxy composite (62/38) were computed using laminate theory in a research done by S. K. Mital et al. [13]. The results are then being compared with three-dimensional Finite Element Analysis (FEA) generated using the MSC Patran Computer Code. The difference in both results is because the FEA analysis also account the loss in axial stiffness due to the waviness of the fibers and matrix rich areas are somewhat lower than they are in the tow areas. The comparison for both methods is shown in Table 2.1.

Table 2.1: Properties of Graphite/Epoxy plain weave composite (62/38) [13].Property(0/90) laminateFinite Element Results

(GPa)72.549.0

(GPa)9.98.8

0.050.09

0.050.08

0.030.03

0.380.53

(GPa)4.64.6

(GPa)3.63.9

The results obtained from the study will be used to compare and validate through experiment done by Yakubu [3]. Figure 2.5 and Figure 2.6 below shows the tensile strength and tensile modulus obtained by Yakubu [3].

Figure 2.5: Tensile strength obtained by Yakubu [3].

Figure 2.6: Tensile modulus obtained by Yakubu [3].

CHAPTER 3METHODOLOGYThis chapter presents process flow diagram, research methodology and tools required in the project.3.1Process Flow DiagramSTARTLiterature review.i. Classical lamination theory.ii. Equation for ply properties.iii. Woven fiber composite.

Obtain mechanical properties of POM and woven kenaf.Calculate ply properties of the composite.Input all the ply property into The LaminatorValidate the numerical data with the experimental result.Data analysis.ENDResult and discussion.Conclusion and recommendationYESNOFigure 3.1: Process flow chart.

Figure 3.1 below shows the methodology planned for the implementation of this project.

3.2Mechanical properties of POM and kenaf yarnPOM FM090 grade will be used as matrix and kenaf yarn imported from Bangladesh will be used as natural fiber reinforcement. The material properties for this composite system are shown in Table 3.1.

Table 3.1: Mechanical properties of POM and kenaf fiber [14, 15].PropertiesKenaf FiberPOM Matrix

Tensile Strength (GPa)0.60.06

Compressive Strength (GPa)0.0570.031

Modulus (GPa)302.54

Fiber Diameter (mm)0.2-

Density (g/cm2)1.31.42

Shear Modulus (GPa)-0.93

Poissons Ratio0.20.35

Thermal Expansion Coefficient (/K)-10410-6

Shear Strength-0.062

3.3Tools Required3.3.1Laminator SoftwareLaminator is an engineering program that analyzes laminated composite plates according to classical laminated plate theory. Table 3.2 shows input and output included in the software.Table 3.2: Input and output included in Laminator [16].InputOutput

Ply material properties Material strengths Ply fiber orientation Stacking sequence Mechanical load Temperature/moisture load Apparent laminate material properties Ply stiffness Compliance matrices Laminate ABD matrices Laminate loads Mid-plane strains Ply stresses Strains in global Material axes Load factors for ply failure

3.4Key Milestone & Gantt ChartThe time allocate for project completion is 28 weeks. In order to aid the student for this project, Gantt chart has been produced. The Gantt chart was shown in Table 3.3.Table 3.3: Project Gantt chart.

CHAPTER 4PROJECT PROGRESS AND FUTURE WORKS

4.1Ply properties of the compositeDifferent type of laminate arrangement and orientation will be used in this study to simulate both unidirectional and woven behavior of kenaf fiber. Therefore, a micromechanics calculator which is also included in the software was being used to estimate lamina properties for given fiber and matrix properties. Table 4.1 shows the ply properties of the composite.

Table 4.1: Ply properties of the composite.PropertiesPOM/kenaf (80/20)POM/kenaf (70/30)

Longitudinal Modulus E1 (GPa)8.03210.78

Shear Modulus G12 (GPa)0.620.5

Longitudinal Poisson V12 0.320.31

Transverse Poisson V210.07360.0438

Longitudinal Thermal Expansion CTE1 (10-6/K)26.3117.16

Transverse Thermal Expansion CTE2 (10-6/K)103.993.05

Longitudinal Tensile Strength Xt (GPa)0.13390.1796

Density (g/cm3)1.3961.384

4.2 Future WorksThe future work for this study is to use all the data to calculate the tensile strength and modulus using Laminator software that will be prepared to analyze multilayered plate. The result obtained will then be validated with the existing experimental results.

REFERENCES

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