Elastic phase-strain distribution in a particulate-reinforced metal-matrix composite deforming by slip or creep
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I. INTRODUCTION
THE interest in metal-matrix composites (MMCs) in recent years has been motivated by their enhanced properties as compared to the unreinforced matrix, e.g., an improved specific stiffness, strength, and wear resistance and a tailorable coefficient of thermal expansion (CTE).[1] Furthermore, the reinforcing phase of an MMC has a higher creep resistance than the matrix at a given temperature, thus improving the creep properties of the composite as compared to the unreinforced matrix.[2] At any temperature, the strength of a composite depends both on the level of indirect matrix strengthening (e.g., due to an increased dislocation density or increased precipitation from the presence of the reinforcing phase) and on direct strengthening from load transfer between the matrix and reinforcing phase. These issues are particularly relevant when the reinforcing phase is discontinuous. If a high proportion of the applied load is carried by the reinforcing phase, the composite is efficient. The level of load sharing is dependent on reinforcement volume fraction, shape, and orientation and on the relative elastic properties of the phases.[3] It is reasonable to assume that the partitioning ratio of an applied load between the matrix and reinforcement will remain constant with increasing applied load, provided that both phases remain elastic. However, once the stress levels in the composite (usually in the matrix) are high enough for relaxation or inelastic deformation processes to occur, the load-partitioning ratio changes. Many models have been developed to predict the load sharing between phases[3,4] of a composite. One approach for evaluating their validity is to measure the mean phase MARK R. DAYMOND, formerly with the Lujan Center, Los Alamos Neutron Science Center, Los Alamos National Laboratory, is with the ISIS Facility, Rutherford Appleton Lab., Chilton, OX11 0QX, United Kingdom. CHRISTIAN LUND, formerly with the Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02319, is with Seagate Corp., Minneapolis, MN 55437. MARK A.M. BOURKE is with the Lujan Center, Los Alamos Neutron Science Center, Los Alamos National Laboratory, Los Alamos, NM 87545. DAVID C. DUNAND, formerly with the Department of Materials Science and Engineering, Massachusetts Institute of Technology, is with the Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208. Manuscript submitted November 10, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS A
stresses using Bragg (elastic) neutron diffraction.[3,5,6] For example, room-temperature in-situ measurements of load partitioning in the phases of discontinuous Al/SiC and Al/ TiC MMCs[3,7,8] have shown that, once the aluminium matrix yields, its capability to bear further increases in load is reduced, so that the reinforcing phase carries a greater proportion of the load. The majority of diffraction-based studies of in-situ loading of MMCs reported to date have been carried out at room temperature. Howe
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