日本金属学会誌

J. Japan Inst. Metals, Vol. 59, No. 8 (1995),
pp. 788-792

Internal Friction and Microplasticity of Carbon-Fiber-Reinforced SiC Ceramics

Hiroyuki Ogawa, Yoichi Nishino and Shigeru Asano

Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya

Abstract:

Mechanical responses of carbon-fiber-reinforced SiC ceramics before fracture were measured in the strain range below 2{×}10-3 by two experimental methods: mechanical hysteresis and internal friction. Load-deflection curves were obtained by the three-point bending deformation in loading-unloading cycles. A little permanent strain was found after the first cycle even in the range where fracture never occurred. A closed hysteresis loop was observed after several cycles and stabilized with a symmetrical shape after more than twenty cycles. Such a stabilized hysteresis loop is attributed to the steady-state microplastic deformation and may cause the amplitude-dependent internal friction.
Internal friction was measured in the fundamental mode of free-free resonant vibration as a function of strain amplitude. With increasing the amount of prestrain in the bending deformation, internal friction increased and became sensitive to the strain amplitude. The amplitude-dependent internal friction in the composites is considered to originate from fiber pull-out or microcrack propagation. The internal friction data were analyzed on the basis of the microplasticity theory and converted into the plastic strain expressed as a function of stress. Therefore, it becomes possible to non-destructively study the forerunning process of fracture of the fiber-reinforced ceramics.


(Received December 21, 1994)

Keywords:

carbon fiber, fiber reinforced ceramics, SiC, mechanical hysteresis, internal friction, amplitude dependence, microplasticity, fracture


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