炭化ケイ素ウイスカー強化型窒化ケイ素セラミツクスに生じる破面間相互作用

抄録

For two kinds of Si₃N₄-based ceramic composites reinforced with SiC whisker with different size, in the present study, the crack opening displacement (COD) was measured in situ in the scanning electro microscope (SEM). The magnitude of the shielding effect was evaluated by comparing it with a theoretical COD profile in an elastic body proposed by Irwin. The composite reinforced with smaller whisker did not exhibit noticeable crack-face interaction. For the composite reinforced with larger whisker, on the other hand, a shielding interaction due to elastic bridging by SiC whisker was recognized, leading to a remarkable rising-curve behavior. Stress intensity factor at crack tip, K_tip and crack propagation resistance due to whisker bridging, K_μ (a) linearly increased with increasing crack opening load. This suggested that the main bridging contribution in a region immediately behind the crack tip (approximately 150μm) is of an elastic nature. After whisker developing closure stress due to elastic bridging, relatively weak frictional bridging between whisker and matrix was also identified during crack propagation.