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

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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