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Chapter 15 Composite Materials:

Chapter 15 Composite Materials Mechanical Behavior of Materials

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

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(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.) Different Composites

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Microstructure of a 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.) Microstructure of a Silicon Carbide Particle

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

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

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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.) Elastic Moduli

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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. Particle Reinforcement

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Determination of V min and V crit. Strength of Composites

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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.)

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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.) Mullite Fiber

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

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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

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

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

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

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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. Failure Modes in Composites

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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. Interface Fracture Toughness

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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. Monolithic Material

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Schematic of a performance chart of a composite

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Shear coupling in a fiber composite

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Unidirectional and cross-plied composites

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

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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. Functionally Graded Materials

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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.) ACCR

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

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Tile Structure of Nacreous Portion of Albalone

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

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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.) Laminate with Aluminum and Silicon Carbide

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