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裂功（WOF）测量问题进行了研究。断裂过程中的WOF测量也仔细考虑裂纹路径和复合材料的微观结构之间的相关性。结果表明，由于C/C或SiC/SiC复合材料试样在冲击试验中很容易断裂成两段，因此Sharpy冲击试验适合于WOF的测量。然而，为了以高精度评估WOF，测量的WOF值应该高于几kJ/m^2。冲击和静态3点弯曲试验测得的WOF值之间的差异不显著，证实了Sharpy冲击试验用于WOF测量的有效性。此外，它被发现，WOF值强烈地依赖于跨度的比的宽度的弯曲梁，S/W。显着的依赖性WOF上的S/W归因于弹性应变能存储在试样和层间剪切和/或剥离断裂。两者均以S/W表示，前者与断裂过程无关，后者与试样的断裂有关。结果表明，大范围的层间断裂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.