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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.

用声发射技术表征了陶瓷材料在热冲击断裂过程中的微观再加工过程。试样为厚度0.5mm、直径20 mm的氧化铝圆片。将圆盘试样加热到指定温度（410 - 460 ℃），用金属棒接触圆盘中心部分进行淬火。在金属棒的另一侧安装了一个带有放大器的声发射传感器，用于检测热冲击断裂过程中由于微裂纹引起的声发射信号，具有很好的灵敏度。采用点式红外测温仪测量了试件表面的温度分布，并对二维热应力场进行了解析计算。通过有限元计算对热应力场进行了分析，并与实验估算的应力场进行了验证。用录像系统观察宏观断裂行为，并在最大应力前观察宏观主裂纹的起始。从另一方面来说。当主裂纹开始时，检测到AE信号显著增加。从这些结果可以看出，热冲击再加工过程包括与金属棒接触后立即产生微裂纹、由于微裂纹的合并而形成主裂纹以及随后的裂纹扩展。此外，还利用声发射技术研究了氧化铝圆盘试样在平面弯曲试验过程中的微断裂过程。因此，热冲击时主裂纹形成的临界应力与机械加载试验的临界应力是等效的。