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Experimental Studies on Energy Release Rate and Bifurcation Process of Fast Propagating Cracks

快速扩展裂纹能量释放速率及分叉过程的实验研究

基本信息

批准号：
12650082
负责人：
SUZUKI Shinichi
金额：
$ 2.43万
依托单位：
Toyohashi University of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12650082/
关键词：
Fracture mechanics Impact strength Experimental stress analysis Brittle fracture Fracture toughness High-polymer materials Crack opening displacement Crack propagation き裂分岐光計測

项目摘要

Two kinds of experimental studies were carried out to figure our the bifurcation mechanism of fast propagating cracks.[1] Fast Propagating cracks at bifurcation were photographed with high-speed holographic microscopy. Crack speed was more than 650m/s. The photographing was done within 10μs before and after bifurcation, and the following results were obtained.(1) Crack opening displacements, CODs, are proportional to the distance r from the crack tip before bifurcation. After bifurcation CODs of mother cracks are proportional to r from the nominal tip of the mother cracks.(2) The energy release rate obtained from the CODs increases gradually and continuously across the bifurcation points of the cracks. Discontinuous change of the energy release rate doesn't occur at the bifurcation.(3) The energy flux toward the crack tips also increases gradually and continuously at the moment of crack bifurcation, and doesn't show discontinuous change. This is caused by the fact that the crack dosen't decelerate discontinuously after crack bifurcation.[2] Two optical systems were applied to take photographs of rapidly bifurcating cracks on the both surfaces of the plate specimens, and the following results were obtained.(1) There are some bifurcating cracks whose shape on one surface of a specimen is apparently different from that on the other surface. In these cases, the crack bifurcations are not two dimensional phenomena, but three dimensional ones.(2) In the above cases, some crack branches keep developing and break up the specimens.(3) Even in the case that cracks have similar shape on the both surface of specimens, two crack branches have different opening displacement. This means that bifurcation is not symmetric with respect to the line along the mother crack.[3] The continuous increase of energy release rate across the bifurcation point may be caused by the three dimensional nature of crack bifurcation.

本文通过两种实验研究来揭示快速扩展裂纹的分叉机理。[1]用高速全息显微镜拍摄了分叉处快速扩展裂纹的照片。裂纹速度大于650 m/s。在分叉前后10μs内进行拍照，得到以下结果。(1)裂纹张开位移（COD）与分叉前距裂纹尖端的距离r成正比。分叉后母裂纹的COD与距母裂纹名义尖端的r成正比。(2)从COD得到的能量释放率逐渐增加，并在整个裂纹的分叉点连续。在分叉处能量释放率没有发生不连续的变化。(3)在裂纹分叉时刻，向裂纹尖端的能流也是逐渐连续增加的，而不是不连续的变化。这是由于裂纹分叉后不再间断减速的结果。[2]采用两套光学系统对板试件的两个表面上的快速分叉裂纹进行了拍摄，得到了以下结果。(1)在试件的一面和另一面存在着形状明显不同的分叉裂纹。在这些情况下，裂纹分叉不是二维现象，而是三维现象。(2)在上述情况下，一些裂纹分支继续发展，并打破了试样。(3)即使在试件两表面裂纹形状相似的情况下，两个裂纹分支的张开位移也不同。这意味着分叉相对于沿沿着母裂纹的线是不对称的。[3]裂纹分叉的三维性可能是导致能量释放率在分叉点处不断增加的原因。