Dynamic Detection of Microcracking by Acoustic Emission during Thermal Shock Fracture of Ceramicsand Analysis of Failure Mechanism

陶瓷热震断裂过程中声发射微裂纹的动态检测及失效机理分析

基本信息

批准号：
09650111
负责人：
WAKAYAMA Shuichi
金额：
$ 2.05万
依托单位：
TOKYO METROPOLITAN UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09650111/
关键词：
Ceramics Thermal Shock Fracture Acoustic Emission Main Crack Formation FractureMechanism Thermal Stress FEM Analysis

项目摘要

Microfractureprocess in ceramics under thermal shock fracture was characterizedby acoustic emission technique. The specimen was alumina disc with 0.5 mm thicknessand 20 mm diameter. The disc specimen was heated to the designated temperature(410 - 460ﾟC) and the central part of disc was quenchedby means of contacting of metal rod. An AE transducer, in which amplifier is instrumented was attached on the opposite side of the metal rod and used for detectingthe AE signals due to microcrackings during thermal shock fracture with excellent sensitivity. The temperature distribution on the specimen was measured by the spot-type infrared thermometer and then the 2-dimensional thermal stress field was calculated analytically. The thermal stress field was also analyzed by FEM calculation and the experimentally estimated stressfield was verified. Macroscopicfracturebehavior was observed using a video systemand the initiation of macroscopicmaincrack was observed before maximum stress. On the other hand. the remarkable increase of AE signals was detected when the maincrack was initiated. From these results, it was understood that the thermal shock fractureprocess consists of microcrackinitiation immediately after contacting a metal bar, maincrack formation due to the coalescence of microcracks and the subsequentcrack propagation. Furthermore the microfracture process during plane bending tests of alumina disc specimens were also investigated by acoustic emission technique. Consequently, it was understood that the critical stress for maincrack formation during thermal shock was equivalentto that of mechanical loaded tests.

在热休克断裂下的陶瓷中的微骨骨折被表征了声发射技术。样品是厚度为0.5 mm的氧化铝盘，直径为20 mm。将光盘样品加热到指定的温度（410-460°C），盘的中心部分是接触金属棒的手段。 AE换能器在金属棒的另一侧连接了一个AE换能器，并用于检测AE信号，这是由于在热休克断裂过程中具有出色敏感性的微裂纹而引起的。通过点型红外温度计测量样品上的温度分布，然后通过分析计算二维热应力场。还通过FEM计算分析了热应力场，并验证了实验估计的应力场。使用视频系统和最大应力之前，观察到宏观crack的倡议，观察到宏观分裂的行为。另一方面。当启动大裂缝时，检测到AE信号的显着增加。从这些结果中可以理解，热休克裂缝普罗克斯在接触金属棒后立即由微裂缝组成，由于微裂纹的合并而导致的Main Crack形成和随后的裂纹繁殖。此外，还通过声发射技术研究了氧化铝盘样品平面弯曲试验期间的微裂纹过程。因此，众所周知，在热休克期间，Maincrack形成的临界应力等效于机械负载测试。