压应力对压剪裂纹扩展的影响研究

本文针对压剪裂纹的启裂及扩展问题,研究了脆性材料中裂纹面压应力变化对其扩展的影响规律.借助双轴加载试验机可自由调节两个轴位移和力的优势,设计了一种单边对称双裂纹压剪试样.试验中,施加裂纹面压应力至不同的预设值后,使剪应力单调增大直至裂纹启裂及扩展,得到不同预设压应力下压剪裂纹启裂及扩展规律. 随着预设压应力增大,启裂角增大,裂纹扩展路径与初始裂纹的偏角也增大.但随着压应力增大,启裂角增大至一定值后趋于稳定,实验发现,依据裂纹是否闭合,压应力对压剪裂纹扩展的作用大致可分为两个阶段:闭合前,压应力对裂纹启裂载荷及启裂角、扩展路径均有影响,预设压应力增大,裂纹启裂载荷增大、启裂角增大,扩展路径愈来愈偏离初始裂纹方向;闭合后,压应力虽然增大,启裂角和临界压剪应力比始终恒定,压应力对临界剪力和扩展路径存在一定影响.研究表明,裂纹启裂角与启裂时的压剪应力比存在一定的对应关系.启裂时的压剪应力比增大,启裂角增大,启裂时的压剪应力比恒定,启裂角不变. 

STUDY ON THE INFLUENCE OF COMPRESSIVE STRESS ON THE COMPRESSION SHEAR CRACK PROPAGATION1)

In this paper, the problem of crack initiation and propagation under compression shear load is investigated experimentally. The influence of far-field compression stress perpendicular to the crack surface on the initiation and propagation of the crack in brittle material is emphasizeded. With the help of the two-axis loading test machine, the two shaft displacements and forces can be adjusted freely during loading. Thus a kind of single-edge symmetric double-crack compression-shear specimen is designed. During the loading, the compression stress stoped as it reaches a series of preset values, while the shear stress increases monotonically till to the crack initiation and propagation. Then the crack initiation and propagation law of compression shear crack under different preset compression stresses can be obtained. It can be find from the test that as the compression stresses relatively smaller, along with the preset compression stress increases, the crack initiation angle increases and the deviation of crack propagation path from the initial crack direction changes severely. As the compression stress reached a definated value, the initiation angle is not changed. It can be find from the test sample that the two crack surfaces are contacted after this definated value of compression stress. The results show that the effect of compression stress on the crack propagation can be divided into two stages according to whether the crack surface contacted or not. Before the crack closed, the influence of compression stress on crack initiation load, crack initiation angle and propagation path increases,when the preset compression stress increases the crack initiation load and the crack initiation angle increase, and the propagation path deviates from the initial crack direction severely. After the crack closed, although the compression stress increases, the crack initiation angle and the critical compression shear stress ratio are keep unchanged. In addition, there existes a certain correspondence between the crack initiation angle and the compression-shear stress ratio at the time of crack initiation. When the ratio of compression-shear stress at the crack initiation increases, the crack initiation angle increases, and vice versa.