Failure of SiC particulate-reinforced metal matrix composites induced by laser thermal shock
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I.
INTRODUCTION
OVER the last decade, the desire for lighter materials with high specific strength and stiffness has led to the development of a range of composite materials as serious alternatives to traditional engineering alloys. Particular interest in the aerospace industry has been directed toward ceramic-reinforced metal matrix composites (MMCs). For applications where high strength and modulus are required, especially at elevated temperatures, for example, in aeroengines, interest has centered around continuous fiber-reinforced titanium alloys.[1] Where less extreme properties are required, however, lower cost aluminum matrix reinforced with a discontinuous phase in the form of particles or whiskers has been the subject of increasing investigation.[2,3,4] These materials have the additional advantages of superior mechanical properties (such as high specific elastic modulus, high specific yield strength, and good wear resistance) and alloying fabrication by conventional metallurgical and mechanical processes.[5,6] In this area, SiC has become the main candidate for use as a reinforcing material. SiC exhibits good thermal conductivity and chemical compatibility with aluminum, forming an adequate bond with the matrix, without developing embrittling intermetallic phases if long periods of liquid metal contact are avoided, e.g., by powder or spray forming,[7] and thereby offering significant advantages over competitors such as boron, graphite, and alumina. However, it is well known that in aerospace engineering, many structural components are subject to severe thermal loadings that may be produced by aerodynamic heating, by laser irradiation, or by localized intense fire.[8,9] Thermal shock may give rise to intense thermal stresses in the comY.C. ZHOU, Professor, is with the Department of Physics, Xiangtan University; also with the Laboratory for Laser and Dynamic Behaviors of Materials, Institute of Mechanics, CAS. Z.P. DUAN, Professor, is with the Laboratory for Laser and Dynamic Behaviors of Materials, Institute of Mechanics, CAS, Beijing 100080, People’s Republic of China. Q.B. YANG, Professor, is with the Department of Physics, Xiangtan University, Xiangtan 411105, Hunan, People’s Republic of China. Manuscript submitted March 25, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS A
ponents around cracks and other kinds of defects and especially in the components of ceramic-reinforced MMCs as a result of the thermoelastic mismatch in the metal and ceramic. The concentration of thermal stresses around defects often results in catastrophic failure. The development of a general methodology for durability and damage analysis for aerospace structures exposed to intense thermal shock will require a materials property database at elevated temperatures, a fracture mechanics solution technique for determining thermal stress intensity factor, and studies of fracture behavior.[9,10,11] Although the problem is very complicated, the present investigation experimentally examines the fracture behavior of SiC particulate-rein
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