Toughening Mechanism of Ceramic Based Composites for Dynamic Crack Propagation

在整个项目期间，对陶瓷纤维增强陶瓷基复合材料的断口功（WOF）测量问题进行了研究。考虑到裂纹路径与复合材料显微组织之间的关系，对WOF测量过程中的断裂过程也进行了详细研究。发现锐利冲击试验适合于WOF的测量，因为通过冲击试验很容易将C/C或SiC/SiC复合材料等试样断裂成两块。然而，为了高精度地评估WOF，测量的WOF值应该高于几个kJ/m^2。剧烈冲击试验测量的WOF值与静态三点弯曲试验测量的WOF值之间的差异不显著，证实了剧烈冲击试验测量WOF的有效性。此外，还发现wof值在很大程度上取决于弯曲梁的跨度与宽度之比S/W。WOF对S/W的显著依赖归因于试样中储存的弹性应变能以及层间剪切和/或脱粘断裂。两者均以S/W表示，其中S/W一方面与断裂过程无关，而S/W则与试件的断裂有关。结果表明，层间断裂的较大程度显著提高了复合材料的wof值。

The problem on the Work-Of-Fracture (WOF) measurement of ceramic matrix composites reinforced with ceramic fibers has been examined throughout the term of the project. Fracture processes during the WOF measurement has also scrutinized considering the correlation between crack path and the microstructure of the composite. It was found that the sharpy impact test was suitable for the WOF measurement, because it was rather easy to rupture a specimen such as C/C or SiC/SiC composite into two pieces through the impact test. The WOF-value measured, however, should be higher than a few kJ/m^2 in order to evaluate WOF with high precision. The validity of the sharpy impact test for WOF measurement was confirmed by the insignificant difference between WOF-values measured by the impact and the static 3-point bend tests. Furthermore, it was found that the WOF-value strongly depended on the ratio of Span to the Width of a bend beam, S/W.The remarkable dependence of WOF on S/W was attributed to elastic strain energy stored in the specimen and interlayer shear and/or debonding fracture. Both of them were given in terms of S/W, while the former was regardless of the fracture process on the one hand, the latter occurred with relation to the rupture of the specimen. It was found that the large extent of the interlayer fracture remarkably increased the WOF-value of the composite.