Study on crack initiation in ceramic materials by ushing hybrid-observing systems

陶瓷材料裂纹萌生的混合观测系统研究

基本信息

批准号：
10555233
负责人：
UENO Akira
金额：
$ 2.62万
依托单位：
Toyota Technological Institute
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2001
项目状态：
已结题

项目摘要

In this study, following four subjects were investigated.(1) A Monte-Calro simulation taking into account the defects size distribution and the micro-crack propagation behavior was conducted by using virtual bending specimens. For the cases of the simulation using micro-crack propagation behavior, the estimated bending strength well coincided with the factual bending strength. Through the evaluation of the effects of scatter in a crack propagation rate, it is reconfirmed that the wide scatter in fracture strength mainly originated from the scatter of defect size.(2) Fatigue crack initiation and propagation in smooth specimens of a sintered Si_3N_4 have been investigated under a static fatigue conditions. Naturally initiated small cracks in smooth specimens propagate with stress-intensity factors which are far lower than the apparent threshold stress-intensity factor of artificial long cracks. In some cases, small crack stops propagation or propagates very slowly after the crack initiation. In case of a naturally initiated small crack, the effect of cyclic loading on the propagation behavior is less than that of artificial long crack. Also, using the AFM, we can detect the some evidence of grain-bridging degradation on the naturally initiated small cracks.(3) To evaluate the crack initiation properties in ceramic materials, photon emission are measured by using a photon multifier tube. A lot of photon are emitted at the instant of fracture. Photon emission continues for a little while. In case of Si_3N_4, photon count number increases gradually by the fracture. It is considered that this phenomen on caused by crack initiation.(4) In this study, crack propagation behavior on glass have been studied by using the newly developed in-situ type bi-axial bending machine. The threshold stress intensity under mixed mode tends to decrease with increase in the stress mixing ratio R. The criteria in which the crack began to grow under mixed mode condition were proposed.

在这项研究中，研究了四个受试者。（1）考虑到缺陷尺寸分布和微裂缝传播行为，通过使用虚拟弯曲标本进行了微裂缝的传播行为。对于使用微裂缝繁殖行为进行仿真的情况，估计的弯曲强度与事实弯曲强度非常相吻合。通过评估裂纹传播速率散射的影响，可以重新确认断裂强度的宽散射主要源于缺陷大小的散射。（2）在静态疲劳条件下研究了烧结的SI_3N_4平滑标本中的疲劳裂纹启动和传播。在平滑标本中，自然引发的小裂纹会以应力强度因子繁殖，远低于人造长裂纹的明显阈值应力强度因子。在某些情况下，裂纹开始后，小裂纹停止繁殖或繁殖非常缓慢。如果天然引发的小裂纹，循环载荷对传播行为的影响小于人造长裂纹的影响。同样，使用AFM，我们可以检测到自然启动的小裂纹上晶粒桥的降解的一些证据。（3）为了评估陶瓷材料中的裂纹启动性能，使用光子多效管管来测量光子发射。骨折的瞬间发出了许多光子。光子发射持续一会儿。在SI_3N_4的情况下，光子计数数逐渐增加。据认为，这种现象是由裂纹引发引起的。（4）在这项研究中，已经使用新开发的位于原地的双轴弯曲机通过研究了玻璃上的裂纹传播行为。混合模式下的阈值应力强度倾向于随着应力混合比的增加而降低。提出了在混合模式条件下裂缝开始生长的标准。