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COMPOSITE MATERIALS

Dr.Suat CANOĞULLARI



©2002 John Wiley & Sons, Inc.M P Groover, “Fundamentals of

Modern Manufacturing 2/e”

Composite Material Defined

A materials system composed of two or morephysically distinct phases whose combination

produces aggregate properties that are

different from those of its constituents

• Examples:

– Cemented carbides (WC with Co binder) – Plastic molding compounds containing fillers

– Rubber mixed with carbon black





One Possible Classification of

Composite Materials1. Traditional composites – composite materials that

occur in nature or have been produced by

civilizations for many years

– Examples: wood, concrete, asphalt

2. Synthetic composites - modern material systems

normally associated with the manufacturing

industries, in which the components are first

produced separately and then combined in a

controlled way to achieve the desired structure,

properties, and part geometry





Why Composites are Important

• Composites are strong, stiff, light in weight, sostrength-to-weight and are several times greaterthan steel or aluminum

• Fatigue properties are generally better than forcommon engineering metals

• Toughness is often greater too

• Composites can be designed that do not corrode like

steel• Possible to achieve combinations of properties not

attainable with metals, ceramics, or polymers alone





Disadvantages and Limitations of Composite Materials

• 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 and

• Gradually they have a low temperature strength against to

metals





Components in a Composite Material

All composite materials consist of two phases:

1. Primary phase - forms the matrix within which

the secondary phase is imbedded2. Secondary phase - 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 Materials

1. Metal Matrix Composites (MMCs) - mixtures of ceramics and metals, such as cemented carbides andother cermets

2. Ceramic Matrix Composites (CMCs) - Al2O3 and SiCimbedded with fibers to improve properties,especially in high temperature applications

– The least common composite matrix

3. Polymer Matrix Composites (PMCs) - thermosettingresins are widely used in PMCs

– Examples: epoxy and polyester with fiberreinforcement, and phenolic with powders





Functions of the Matrix Material

• Provides the bulk form of the part

• Holds the imbedded phase in place

• 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 thereinforcing agent



Matrix Considerations

End Use Temperature

Toughness

Cosmetic Issues

Flame Retardant

Processing MethodAdhesion Requirements



©2002 John Wiley & Sons, Inc.

M P Groover, “Fundamentals of


The Reinforcing Phase

(Secondary Phase)

• Function is to reinforce the primary phase

• Imbedded phase is most commonly one of thefollowing shapes:

a) Fibersb) Particles

c) Flakes

• In addition, the secondary phase can take the form

of an infiltrated phase in a skeletal or porous matrix

– Example: a powder metallurgy part infiltrated withpolymer



11

Types of Fibers

Fiber Glass

Graphite Fiber

Kevlar Fiber

Kevlar/Carbon Hybrid



Composite Survey

Large-

particle

Dispersion-

strengthened

Particle-reinforced

Continuous

(aligned)

Aligned Randomlyoriented

Discontinuous

(short)

Fiber-reinforced

Laminates Sandwich

panels

Structural

Composites

Adapted from Fig.16.2, Callister 7e .



• Elastic modulus, E c , of composites:-- two approaches.

• Application to other properties: -- Electrical conductivity, se : Replace E in the above equations

with se .

-- Thermal conductivity, k : Replace E in above equations with k .

Adapted from Fig. 16.3,Callister 7e . (Fig. 16.3 isfrom R.H. Krock, ASTM Proc , Vol. 63, 1963.)

Composite Survey

lower limit: 1

E c = V m

E m +

V p

E p

c m m

upper limit: E = V E + V p E p

“rule of mixtures”

Particle-reinforced Fiber-reinforced Structural

Data:Cu matrixw/tungstenparticles

0 20 4 0 6 0 8 0 10 0

150

20 0

250

30 0350

vol% tungsten

E (GPa)

(Cu) ( W)



Composite Survey: Fiber

• Fibers themselves are very strong

– Provide significant strength improvement to

material

Properties are Determined by Three Factors:

• The materials,• The geometric shapes of the constituents and

• Resulting structure of the composite system

Particle-reinforcedFiber-reinforced Structural






Figure 9.5 - (a) Model of a fiber-reinforced composite material showingdirection in which elastic modulus is being estimated by the rule of mixtures (b) Stress-strain relationships for the composite material andits constituents. The fiber is stiff but brittle, while the matrix(commonly a polymer) is soft but ductile.






Figure 9.6 - Variation in elastic modulus and tensile strength as a function

of direction of measurement relative to longitudinal axis of carbon

fiber-reinforced epoxy composite



Fiber Alignment

alignedcontinuous

aligned randomdiscontinuous




Composite Strength: Longitudinal Loading

Continuous fibers - Estimate fiber-reinforced compositestrength for long continuous fibers in a matrix

• Longitudinal deformation

sc =

smV m +

s f V f but

c =

m =

f

volume fraction isostrain

E ce = E m V m + E f V f longitudinal (extensional)modulus

m m

f f

m

f

V E

V E

F

F f = fiber

m = matrix

Remembering: E = s / and note, this modelcorresponds to the“upper bound” for

particulate composites



Composite Strength: Transverse Loading

• In transverse loading the fibers carry less of theload and are in a state of ‘isostress’

s

c

= s

m

= s

f

= s

c

= m

V m

+

f

V f

f

f

m

m

ct E

V

E

V

E

1transverse modulus

Remembering: E = s / and note, this modelcorresponds to the “lower

bound” for particulate

composites



An Example:

Note: (for ease of conversion)

6870 N/m2 per psi!

UTS, SI Modulus, SI

57.9 MPa 3.8 GPa

2.4 GPa 399.9 GPa

(241.5 GPa)

(9.34 GPa)



• Stacked and bonded fiber -reinforced sheets-- stacking sequence: e.g., 0º/90º or 0 /45 /90º

-- benefit: balanced, in-plane stiffness


Composite Survey: Structural

Particle-reinforced Fiber-reinforced Structural

• Sandwich panels -- low density, honeycomb core-- benefit: light weight, large bending stiffness

honeycomb adhesive layer

face sheet

Adapted from Fig. 16.18,Callister 7e . (Fig. 16.18 isfrom Engineered Materials

Handbook , Vol. 1, Composites , ASM International, Materials Park, OH, 1987.)

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