Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
1
Section 1
Introduction to Composites
By definition, composite materials are formed from two or more materials that have quite
different properties.
The resultant material has a heterogeneous microstructure with extraordinary performance
that displays a combination of the best characteristics of the component materials.
Composites are widely used because their overall properties can be engineered through
microstructural design to become superior to those of the individual monolithic
counterparts.
Nature has provided some of the best-performing composites such as seashell , bones,
macadamia nutshells, wood and bamboo.
These natural composites have superior mechanical efficiency in strength, hardness and
toughness compared to many man-made composite materials. These biological composites
display graded structures at several levels of hierarchy with length scales that range from
micro- to nanometres.
For instance, seashells have two to three orders of lamellar structure whilst bone has seven
orders of hierarchy.
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
2
A composite material is a material that has a
chemically and/or physically distinct phases
distributed within a continuous phase. The
composite generally has characteristics better
than or different from those of either
component. The matrix phase is the
continuous phase, while the distributed phase,
commonly called the reinforcement phase,
can be in the form of particles, whiskers or
short fibers, continuous fibers or sheet.
Figure 1 shows the types of composites based
on the form of reinforcement. Oftentimes it is
convenient to classify different types of
composites as per the matrix material
characteristics, viz., polymer matrix
composites (PMCs), metal matrix composites
(MMCs), and ceramic matrix composites
(CMCs).
Fig. 1. Types of composites based on the form of
reinforcement.
History of composite materials
The earliest man-made composite materials were straw and mud combined to form
bricks (unfired) for building construction.
The history of modern composites probably began in 1937 when salesman from
the Owens Coring Fiberglass Company began to sell fiberglass (had been made,
almost by accident in 1930) to interested parties around the United State.
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
3
Fig. .2 Performance of a composite is linked to some important factors : composition of components, their mechanical behavior, processing, and the characteristics of the
interface between matrix and reinforcement.
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
4
Why study composites?
With a knowledge of the various types of composites, as well as an
understanding of the dependence of their behaviors on the
Characteristics
Relative amounts
Geometry / distribution
And properties of the constituent phases.
It is possible to design materials having property combinations that are better than
those found in metals alloy, ceramics, and polymeric materials alone.
Disadvantages and Limitations of Composite Materials
— Properties of many important composites are anisotropic - the properties differ
depending on the direction in which they are measured – this may be an advantage or a
disadvantage Many of the polymer-based composites are subject to attack by chemicals
or solvents, just as the polymers themselves are susceptible to attack Composite
materials are generally expensive Manufacturing methods for shaping composite
materials are often slow and costly .
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
5
Section 2
Functions of Materials
Nearly all composite materials consist of two phases:
(Primary Phase) Functions Matrix Material
Protect phases from environment
Transfer Stresses to phases
Holds the imbedded phase in place, usually enclosing and often concealing it
When a load is applied, the matrix shares the load with the secondary phase, in some
cases deforming so that the stress is essentially born by the reinforcing agent
(Secondary Phase) Reinforcing
( imbedded phase) sometimes referred to as a reinforcing agent, because it usually
serves to strengthen the composite.
The reinforcing phase may be in the form of fibers, particles, or various other
geometries.
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
6
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
7
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
8
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
9
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
10
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
11
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
12
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
13
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
14
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
15
Section3
Components of reinforcing phase
Fibre
( Oxide and Non-oxide Fibers).
Oxide fibers find uses both as insulation and as reinforcements. Glass fibers, based
on silica, possess a variety of compositions in accordance with the characteristics
desired.
They represent the biggest market for oxide fibers. Unlike other oxide fibers, glass
fibers are continuously spun from the melt and are not used at temperatures above
250°C. Short oxide fibers can be melt blown whilst other aluminasilicate and alumina
based continuous fibers are made by sol-gel processes. Initial uses for these fibers
were as refractory insulation, up to 1600°C, but they are now also produced as
reinforcements for metal matrix composites.
Continuous oxide fibers are candidates as reinforcements for use up to and above
1000°C.
Glass Fibers, Alumina Fibers, Aluminosilicate Fibers
Non-oxide fibers are being considered for many applications, but are currently
being developed and produced primarily as continuous-length structural
reinforcement for ceramic matrix composites (CMC). Since only those fiber types with
compositions based on silicon carbide (SiC) have demonstrated their general
applicability for this application, this chapter focuses on commercially available SiC-
based ceramic fiber types of current interest for CMC and on our current state of
experimental and mechanistic knowledge concerning their production methods,
microstructures, physical properties, and mechanical properties at room and high
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
16
temperatures. Particular emphasis is placed on those properties required for
successful implementation of the SiC fibers in high-temperature CMC components.
It is shown that significant advances have been made in recent years concerning SiC
fiber production methods, thereby resulting in pure near-stoichiometric small-diameter
fibers that provide most of the CMC fiber property requirements, except for low cost.
Filaments of reinforcing material, usually circular in cross-section Diameters range
from less than 0.0025 mm to about 0.13 mm, depending on material Filaments
provide greatest opportunity for strength enhancement of composites .The filament
form of most materials is significantly stronger than the bulk form .As diameter is
reduced, the material becomes oriented in the fiber axis direction and probability of
defects in the structure decreases significantly
Whiskers
whisker reinforced composites exhibit significant improvements in mechanical properties,
such as strength and fracture toughness. These composites are typically densified by pressure-
assisted sintering (i.e. hot-pressing) with SiC whisker contents ranging from 10 to 30 vol.%.
Cutting tools for high nickel alloys are the major application, but other wear and structural
uses are also being developed.
Micro-mechanical modeling and available experimental evidence indicates that the
composite toughness,K (composite), can be described as the sum of the matrix toughness,
(matrix) K, and a contribution due to whisker toughening, ∆K(whisker reinforcement).
In other words,
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
17
where
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
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Particles and Flakes
ranging in size from microscopic to macroscopic
Flakes are basically two‑dimensional particles ‑ small flat platelets
The distribution of particles in the composite matrix is random, and therefore strength
and other properties of the composite material are usually isotropic
Strengthening mechanism depends on particle size
Laminates
Ceramic ,metal, polymer
Flat , Hollow
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
19
Section4
Classification of composites-Matrix
polymer-matrix composites (PMC)
Polymer Matrix Composite (PMC) is the material consisting of a polymer (resin) matrix
combined with a reinforcing dispersed phase.
Polymer Matrix Composites are very popular due to their low cost and simple fabrication
methods.
Use of non-reinforced polymers as structure materials is limited by low level of their
mechanical properties: tensile strength of one of the strongest polymers - epoxy resin is 20000
psi (140 MPa). In addition to relatively low strength, polymer materials possess low impact
resistance.
(advantages of PMC)
Reinforcement of polymers by strong fibrous network permits fabrication of Polymer Matrix
Composites (PMC) characterized by the following properties:
High tensile strength;
High stiffness;
High Fracture Toughness;
Good abrasion resistance;
Good puncture resistance;
Good corrosion resistance;
Low cost.
The main disadvantages of Polymer Matrix Composites (PMC) are:
Low thermal resistance;
High coefficient of thermal expansion.
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
20
Two types of polymers are used as matrix materials for fabrication composites:
1-Thermosets (epoxy, phenolic)
2-Thermoplastics (Low Density Poly-ethylene (LDPE), High Density Poly-ethylene (HDPE),
poly-propylene, nylon, acrylics).
Metal Matrix Composites (MMCs)
— A metal matrix reinforced by a second phase
— Reinforcing phases:
— Particles of ceramic (these MMCs are commonly called cermets)
— Fibers of various materials: other metals, ceramics, carbon, and boron
Examples of matrices in such composites include aluminum, magnesium, and titanium.
Metals are mainly reinforced to increase or decrease their properties to suit the needs of
design.
For example, the elastic stiffness and strength of metals can be increased, and large
coefficient of thermal expansion and thermal and electric conductivities of metals can be
reduced, by the addition of fibers such as silicon carbide.
Advantages of MMC’s
Advantages over polymer matrix composites. These include higher elastic properties; higher
service temperature; insensitivity to moisture; higher electric and thermal conductivities; and
better wear, fatigue, and flaw resistances.
The drawbacks of MMCs over PMCs include higher processing temperatures and higher
densities.
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
21
Ceramic Matrix Composites (CMC)
Ceramic matrix composites (CMCs) have a ceramic matrix such as alumina calcium alumino
silicate reinforced by fibers such as carbon or silicon carbide.
Advantages of CMC’s
• High strength,
• Hardness,
• High service temperature limits for ceramics,
• Chemical inertness, and
• Low density.
However, ceramics by themselves have low fracture toughness. Under tensile or impact
loading, they fail catastrophically.
Types of ceramic composite
Non oxide- Non oxide Composites
Oxide- Oxide Composites;
Non-oxide- oxide Composites;
Glass - Ceramic Composites;
Manufacturing Method of CMC
The most common methods to manufacture ceramic matrix composites are: Processing :
Integration Powders method -
chemically methods:
Melting process;
Heat Pressure Process;
Slip casting
low-pressure sintering;
Reaction sintering;
Pressure-less sintering;
Chemical vapor infiltration;
Directed melt oxidation;
Sol-gel processing;
combustion synthesis
Composite Material technology Materials Engineering Department Dr. Alaa Aladdin
Class: 4th
year 2014-2015 Course 1
Assistant Professor
22
References
1- K. K. Chawla ,CERAMIC MATRIX COMPOSITES,2nd
, SPRINGER
SCIENCE+BUSINESS MEDIA, LLC,2008.
2- M. Low ,Ceramic matrix composites Microstructure, properties and
applications, WOODHEAD PUBLISHING LIMITED ,2006.
3- Narottam P. Bansal ,Handbook of Ceramic Composites, 2005 Kluwer Academic Publishers