Elastic properties of a crossply SiC f /Ti composite at elevated temperatures
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INTRODUCTION
FIBER -reinforced metal-matrix composites are promising materials for components of advanced structures because such composites show high strength and toughness at elevated temperatures. Understanding their elastic properties is important for designing such a structure. Particularly, the complete elastic-constant tensor Cij must be known. However, determination of the complete set of Cij is difficult for such a fiber-reinforced composite for two reasons: (1) it exhibits lower elastic symmetry and possesses many independent elastic stiffnesses (typically, five to nine), and (2) the usual pulse-echo method is inapplicable for some stiffnesses because of wave scattering and mode conversion at the interfaces between the fiber and matrix. Also, deriving the complete set of Cij is never trivial at elevated temperature. In previous studies,[1,2] we developed a contactless measurement method for elastic constants and internal friction of rectangular parallelepipeds of low elastic symmetry, relying on electromagnetic acoustic resonance (EMAR). Using Lorentz-force coupling, we selectively and independently excited one vibration group among eight possible groups of free vibration of a rectangular parallelepiped and determined all elastic-constant and internal-friction components of a silicon-carbide-fiber-reinforced Ti-alloy-matrix cross-ply composite.[2] This metal-matrix composite is a candidate material for components of aerospace structures and jet engines, and elastic properties at elevated temperatures are required. In the present study, we measured the temperature dependence of all elastic-stiffness components of the composite HIROTSUGU OGI, Associate Professor, GOH SHIMOIKE, Graduate Student, and MASAHIKO HIRAO, Professor, are with the Graduate School of Engineering Science, Osaka University, Osaka 560-8531, Japan. HASSEL LEDBETTER, Leader of Physical Properties Group, is with the Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Boulder, CO 80303. KAZUKI TAKASHIMA, Associate Professor, is with the Precision and Intelligence Laboratory, Tokyo Institute of Technology, Kanagawa 226-8503, Japan. Manuscript submitted April 4, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS A
up to 1000 K. The contactless nature of EMAR allows one to perform high-temperature acoustic-resonance measurements without a buffer rod, which is needed between transducers and the specimen in the case of conventional contacting methods. Insertion of such a buffer rod causes background resonance peaks that overlap peaks from the specimen; more seriously, it prevents one from measuring intrinsic internal friction because a large amount of acoustic energy is lost during propagation in the buffer rod. There are important previous studies of acoustic-resonance measurement for isotropic materials at elevated temperatures. Kuokkala and Schwarz[3] deposited a magnetostrictive coating on amorphous Ni80P20 and measured internal friction up to 520 K. The temperature limit depends on the Curie point. Beca
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