Generalized shear-lag model for load transfer in SiC/Al metal-matrix composites
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Seung I. Cha and Soon H. Honga) Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kusung-dong, Yusung-gu, Daejeon, 305-701, Korea (Received 29 July 2003; accepted 18 September 2003)
The load-transfer efficiency of reinforcement, in cylindrical forms in metal-matrix composite (MMC), was analyzed based on the shear-lag model. Both the geometric shape and alignment of reinforcement were considered. The stress transferred to a misaligned whisker was calculated from differential equations based on the force equilibrium in longitudinal and transverse directions. A new parameter, defined as effective aspect ratio, was used to indicate the load-transfer efficiency of misaligned reinforcement. The effective aspect ratio was formulated as a function of aspect ratio and misorientation angle of reinforcement in MMC. A probability density function of misorientation distribution was used to estimate the strengthening effect of all misaligned whiskers distributed in the matrix. Considering the contributions of both effective aspect ratio and misorientation distribution on load-transfer efficiency, a generalized shear-lag model was proposed to explain the mechanical anisotropy of discontinuous reinforced MMC.
I. INTRODUCTION
Metal-matrix composites (MMCs) have the advantages of low density and improved stiffness and strength, and thus are attractive alternatives to high-strength lightweight Al and Ti alloys.1 The advantages of MMCs compared to the monolithic alloys are the higher specific strength, specific modulus, and creep resistance with reasonable ductility. The addition of rigid reinforcement in a ductile matrix results in improved mechanical properties, such as tensile strength, elastic modulus, and creep resistance. Discontinuous silicon carbide-reinforced aluminum alloy composites have received considerable interest due to their excellent mechanical properties with cheaper cost compared to the continuous fiber-reinforced aluminum composite.2,3 Several researchers have investigated mechanical properties of discontinuous silicon carbide-reinforced aluminum matrix composites with a growing interest in MMCs for high-temperature structural applications.4–10 The strengthening mechanism through the load transfer from matrix to reinforcement in composite materials has been formulated by the shear-lag model.11–13 In the shear-lag model, the mechanical properties of composite a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 12, Dec 2003
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can be expressed as a function of the volume fraction and aspect ratio of reinforcement. However, this approach gives a poor estimation of the strengthening effect in the case of short fiber or whisker-reinforced MMCs due to the contribution of load transfer from matrix to end surfaces of reinforcement. Nardone et al.14 modified the shear-lag model for discontinuous reinforced composite by considering the load transfer from matrix
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