Chapter 15Composite Materials

Mechanical Behavior of Materials

Different types ofreinforcement for composites:(a) particle reinforcement;(b) short fiber reinforcement;(c) continuous fiber reinforcement;(d) laminate reinforcement

Reinforcement for Composites

(a) Transverse sectionof a boron fiber reinforcedaluminum composite. Vf = 10%.(b) Section of a short aluminafiber/aluminum matrix composite.(c) Deeply etched transversesection of a eutectic compositeshowing NbC fibers in an Ni–Crmatrix. (Courtesy of S. P. Cooperand J. P. Billingham, GEC TurbineGnerators Ltd, U.K.)

Different Composites

Microstructure of asilicon carbide particle (10, 20, and30%, three different volumefractions) reinforced aluminiumalloy (2080) matrix compositesmade by hot pressing of powdersfollowed by hot extrusion. Notethe preferential alignment of SiCparticles in the extrusion direction.The number and subscript pindicate the volume fraction of SiCparticles in the composites.(Courtesy of N. Chawla.)

Microstructure of a Silicon Carbide Particle

TEM micrographshowing dislocations in aluminumin the region near a silicon carbideparticle (SiCp).

Interfacial Interaction

Simple compositemodels. (a) Longitudinal response(action in parallel). (b) Transverseresponse (action in series).

Simple Composite Models

An example of a linearincrease in the longitudinalmodulus of the composite, Ecl, as afunction of the volume fraction offiber for a glass fiber-reinforcedepoxy. (After R. D. Adams and D.G. C. Bacon, J. Comp. Mater., 7(1973) 53.)

Elastic Moduli

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

Particle Reinforcement

Determination of Vmin and Vcrit.

Strength of Composites

Strength in Silicon Carbide Whisker /alumina Composites

Increase in strength insilicon carbide whisker/aluminacomposites as a function of thewhisker volume fraction and testtemperature. (After G. C. Wei andP. F. Becher, Am. Ceram. Soc. Bull.,64 (1985) 333.)

Stress vs. displacement curves for mullitefiber (Nextel 550)/mullite matrixin three-point bending. Theuncoated one refers to themullite/mullite composite with nointerfacial coating, which shows acatastrophic failure. Thecomposite with a double interfacialcoating of SiC and BN shows anoncatastrophic. (Adapted from K.K. Chawla, Z. R. Xu, and J.-S. Ha, J.Eur. Ceram. Soc., 16 (1996) 293.)

Mullite Fiber

Perturbation of the matrix stress state due to the presence of fiber.

Load Transfer from Matrix to Fiber

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

Fiber and Matrix Elastic

Variation in the fiber load transfer length as a functionof the aspect ratio /d

Fiber Elastic and Matrix Plastic

Optical micrograph of multiple fracture of tungstenfibers in an Fe–Cu matrix.

Multiple Fracture

Scanning electron micrographs of fracture incomposites, showing the fiber pullout phenomenon. (a)

Carbon fiber polyester. (b) Boron fiber aluminum 6061.

Fracture in Composites

Fracture of weakinterface in front of crack tip dueto transverse tensile stress; m andf indicate the matrix and fiber,respectively. (After J. Cook and J.E. Gordon, Proc. Roy. Soc. (London),A 228 (1964) 508.)

Crack front andcrack wake debonding in a fiberreinforced composite.

Failure Modes in Composites

The ratio of theinterface fracture toughness tothat of fiber, Gi/Gf, vs. the elasticmismatch α. Interfacial debondingoccurs under the curve, while forconditions above the curve, thecrack propagates through theinterface.

Interface Fracture Toughness

Schematic ofvariation in elastic moduli of a fibercomposite and a monolithicmaterial with the angle ofreinforcement. Ea is the axialYoung’s modulus, vat is theprincipal Poisson’s ratio, and Ga isthe axial shear modulus.

Monolithic Material

Schematic of a performance chart of a composite

Shear coupling in a fiber composite

Unidirectional and cross-plied composites

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

Weibull Plot

Schematic of afunctionally graded materialbetween a ceramic on theleft-hand side and a metal on theright-hand side. Also shown aremicropores and additives.

Functionally Graded Materials

Cross-section of analuminium composite conductorreinforced (ACCR) cable. Thecentral wires consist of continuousalumina fibers in an aluminiummatrix composite while the outerwires are made of Al–Zr alloy.(Courtesy of 3M Co.)

ACCR

Flexural strength forselected monolithic and laminatedmaterials. (Adapted from M.Sarikaya, Micr. Res. Tech., 27 (1994)371.)

Tile Structure of Nacreous Portion of Albalone

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

PMC

Cross-section of alaminate consisting of aluminiumand silicon carbide: (a) SEM; (b)TEM. From X. Deng, K. K. Chawla,M. Koopman, and J. P. Chu, Adv.Eng. Mater., 7 (2005) 1.)

Laminate with Aluminum and Silicon Carbide