1. Chapter 15 Composite Materials
Mechanical Behavior of Materials

2. Reinforcement for Composites
Different types of
reinforcement for composites:
(a) particle reinforcement;
(b) short fiber reinforcement;
(c) continuous fiber reinforcement;
(d) laminate reinforcement

3. Different Composites (a) Transverse section
of a boron fiber reinforced
aluminum composite. Vf = 10%.
(b) Section of a short alumina
fiber/aluminum matrix composite.
(c) Deeply etched transverse
section of a eutectic composite
showing NbC fibers in an Ni–Cr
matrix. (Courtesy of S. P. Cooper
and J. P. Billingham, GEC Turbine
Gnerators Ltd, U.K.)

4. Microstructure of a Silicon Carbide Particle
silicon carbide particle (10, 20, and
30%, three different volume
fractions) reinforced aluminium
alloy (2080) matrix composites
made by hot pressing of powders
followed by hot extrusion. Note
the preferential alignment of SiC
particles in the extrusion direction.
The number and subscript p
indicate the volume fraction of SiC
particles in the composites.
(Courtesy of N. Chawla.)

6. Interfacial Interaction
TEM micrograph
showing dislocations in aluminum
in the region near a silicon carbide
particle (SiCp).

7. Simple Composite Models
models. (a) Longitudinal response
(action in parallel). (b) Transverse
response (action in series).

8. Elastic Moduli An example of a linear increase in the longitudinal
modulus of the composite, Ecl, as a
function of the volume fraction of
fiber for a glass fiber-reinforced
epoxy. (After R. D. Adams and D.
G. C. Bacon, J. Comp. Mater., 7
(1973) 53.)

9. Particle Reinforcement
Schematic of increase in modulus in a composite with reinforcement volume fraction for
a different form of reinforcement – continuous fiber, whisker, or particle. Note the loss of
reinforcement efficiency as one goes from continuous fiber to particle.

10. Strength of Composites
Determination of Vmin and Vcrit.

11. Strength in Silicon Carbide Whisker /alumina Composites
Increase in strength in
silicon carbide whisker/alumina
composites as a function of the
whisker volume fraction and test
temperature. (After G. C. Wei and
P. F. Becher, Am. Ceram. Soc. Bull.,
64 (1985) 333.)

12. Mullite Fiber Stress vs. displacement curves for mullite
fiber (Nextel 550)/mullite matrix
in three-point bending. The
uncoated one refers to the
mullite/mullite composite with no
interfacial coating, which shows a
catastrophic failure. The
composite with a double interfacial
coating of SiC and BN shows a
noncatastrophic. (Adapted from K.
K. Chawla, Z. R. Xu, and J.-S. Ha, J.
Eur. Ceram. Soc., 16 (1996) 293.)

13. Load Transfer from Matrix to Fiber
Perturbation of the matrix stress state due to the presence of fiber.

14. Fiber and Matrix Elastic
Load transfer to fiber. Variation in tensile stress σ in fiber and shear stress τ along the interface with the fiber length .

15. Fiber Elastic and Matrix Plastic
Variation in the fiber load transfer length as a function
of the aspect ratio /d

16. Multiple Fracture Optical micrograph of multiple fracture of tungsten
fibers in an Fe–Cu matrix.

17. Fracture in Composites
Scanning electron micrographs of fracture in
composites, showing the fiber pullout phenomenon. (a) Carbon fiber polyester. (b) Boron fiber aluminum 6061.

18. Failure Modes in Composites
Fracture of weak
interface in front of crack tip due
to transverse tensile stress; m and
f indicate the matrix and fiber,
respectively. (After J. Cook and J.
E. Gordon, Proc. Roy. Soc. (London),
A 228 (1964) 508.)
Crack front and
crack wake debonding in a fiber
reinforced composite.

19. Interface Fracture Toughness
The ratio of the
interface fracture toughness to
that of fiber, Gi/Gf, vs. the elastic
mismatch α. Interfacial debonding
occurs under the curve, while for
conditions above the curve, the
crack propagates through the
interface.

20. Monolithic Material Schematic of
variation in elastic moduli of a fiber
composite and a monolithic
material with the angle of
reinforcement. Ea is the axial
Young’s modulus, vat is the
principal Poisson’s ratio, and Ga is
the axial shear modulus.

21. Schematic of a performance chart of a composite

22. Shear coupling in a fiber composite

23. Unidirectional and cross-plied composites

24. Weibull Plot
Weibull plot of tensile strength of carbon fiber/epoxy composite. (Courtesy of B. Atadero and V. Karbhari.)

25. Functionally Graded Materials
Schematic of a
functionally graded material
between a ceramic on the
left-hand side and a metal on the
right-hand side. Also shown are
micropores and additives.

26. ACCR Cross-section of an aluminium composite conductor
reinforced (ACCR) cable. The
central wires consist of continuous
alumina fibers in an aluminium
matrix composite while the outer
wires are made of Al–Zr alloy.
(Courtesy of 3M Co.)

27. Flexural strength for
selected monolithic and laminated
materials. (Adapted from M.
Sarikaya, Micr. Res. Tech., 27 (1994)
371.)

28. Tile Structure of Nacreous Portion of Albalone

29. PMC
Schematic of a metal/polymer matrix composite (PMC) such as Arall or Glare.

30. Laminate with Aluminum and Silicon Carbide
Cross-section of a
laminate consisting of aluminium
and silicon carbide: (a) SEM; (b)
TEM. From X. Deng, K. K. Chawla,
M. Koopman, and J. P. Chu, Adv.
Eng. Mater., 7 (2005) 1.)