A Basic Study on the Damage Estimation of Composite Materials by Impact Sound.

本文研制了一种简单的仪器系统，用于根据钢球撞击炉内用细陶瓷线悬挂的小矩形棒材试样（约3*4*50mm）所产生的声音来测定材料的弹性常数。利用快速傅立叶变换分析仪从冲击声中测量了弯曲和扭转振动模式的固有频率，并利用Timoshenko的梁理论和Saint-Venant的扭转理论从这些频率中计算了弹性常数。对于各向同性材料，杨氏模量E、剪切模量G和泊松比v由一个试样确定。结果表明，本文方法计算的弹性常数与ASTM标准方法计算的弹性常数吻合较好。测量了SiC/SiC复合材料在空气中高达1200ºC的高温下的弹性常数。在1000或1100℃的恒温条件下，试样的弹性常数在保温初期随时间的增加而减小，但在保温后期逐渐恢复。采用扫描俄歇纳米探针系统对原始试样和被试试样的表面进行了检测。结果表明，弹性常数在高温下的时间变化是由于碳化硅纤维的炭素涂层氧化和二氧化硅的形成，并且本方法可以方便地从弹性常数的降低来评估材料的损伤。将该方法推广到包括板试样弹性常数的测量。从冲击声出发，测量了SiC/SiC复合材料矩形板（50.0*70.0*2.8mm）弯曲振动的固有频率，并利用有限元法确定了材料的杨氏模量的减小对材料的损伤。最后，从发动机运行前后的冲击声中测量了由SiC/SiC复合材料制成的喷气发动机喷管襟翼的固有频率，并通过材料杨氏模量的降低来估计襟翼的损伤程度。值得注意的是，目前的方法能够测量剪切模量以及高温下的杨氏模量，这是一种简单且成本有效的方法，使用小样本，并且被认为是在开发和操作阶段对材料评估有用。少

A simple instrumentation system is developed for determining the elastic constants of materials from the sound produced by the impact of a steel ball on a small rectangular bar specimen (abt. 3*4*50mm) which is suspended by thin ceramic threads in a furnace. The natural frequencies 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. For isotropic materials, Young's modulus E, shear modulus G and Poisson's ratio v are determined from one specimen. It is demonstrated that the elastic constants obtained by the present method are in good agreement with those determined by the ASTM standard method.The elastic constants of SiC/SiC composite were measured at elevated temperatures up to 1,200ﾟC in air. When the specimen was kept at a constant temperature of 1,000 or 1,100ﾟC, the elastic constants decreas … More ed with time at the early holding stage, but they recovered at the later stage. A scanning Auger nanoprobe system was employed to examine the surfaces of the original and tested specimens. It was shown that the time variation of the elastic constants at high temperatures is attributable to the oxidation of the pyrocarbon coating of the SiC fiber and the formation of silica, and that the present method is conveniently used for evaluating the damage of materials from the reduction of the elastic constants.The present method is extended to include the measurement of elastic constants of a plate specimen. The natural frequencies of bending vibration of a rectangular plate (50.0*70.0*2.8mm) of SiC/SiC composite were measured from the impact sound and the damage of the material as the reduction of Young's moduli was determined by employing a finite element method. Finally, the natural frequencies of a jet engine nozzle flap made of SiC/SiC composite panel were measured from the impact sound before and after engine operation, and the damage of the flap was estimated as the reduction of the Young's modulus of the material. It may be noted that the present method is capable of measuring the shear modulus as well as Young's modulus at high temperatures by a simple and cost effective procedure using small specimens, and is thought to be useful for material evaluation at development and operation stages. Less