A Study on the Propagation of a Brittle Fracture…3 rd Report

Dynamical Stress and Velocity of a Propagating Crack

Abstract

A brittle fracture propagation test was carried out to find relations among the crack propagation velocity, dynamical stress distribution, temperature and applied stress. To simplify the test condition, isothermal double tension test was used and test temperatures were made low enough to get nearly elastic cracks. The test results were compared with the previous calculation and some considerations were made on the surface plastic work-done.
The main results are as follows,
1) The stress distribution around a propagating crack is obviously different from that of a stationary crack. Along the crack path, there is a region where the normal stress perpendicular to it is lower than the mean stress. This minimum stress is depends on the crack velocity. These results show good agreement with the calculations.
2) Crack velocity depends on both temperature and applied stress. When the applied stress is not changed, the lower the test temperature is, the higher the velcoity is and for a temperature the higher the applied stress is, the higher the velocity is. Taking the surface plastic work-done into considerations, this is explained.