Published: Jan 1997
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The isotropic and/or orthotropic elastic constants of ceramic matrix composites are measured from the impact sound of a small rectangular bar specimen which is suspended by thin ceramic threads in a furnace. The natural frequencies at high temperatures of the flexural and torsional vibration modes are measured from the impact sound using a fast Fourier transform analyzer and elastic constants are computed from these frequencies using Timoshenko's beam theory and Saint-Venant's torsion theory. The natural frequencies of a rectangular silicon carbide/silicon carbide (SiC/SiC) plate are also measured at high temperatures and its elastic constants are determined using an iteration technique employing a finite element method. This technique is extended to measure the natural frequencies of a jet engine nozzle flap made of SiC/SiC composite panel from the impact sound before and after engine operation, and thus the damage of the flap is evaluated as the reduction of the Young's modulus of the material.
ceramic matrix composite, orthotropic elastic constant, impactsound, natural frequency, Auger electron microscopy, damage evaluation, nondestructive testing
Professor, Takushoku University, Tokyo,
Director, Composite Materials Center, Aero-Engine & Space Operations, Ishikawajima-Harima Heavy Industries Co., Ltd., Tokyo,