STUDY ON THE INFLUENCE OF COMPRESSIVE STRESS ON THE COMPRESSION SHEAR CRACK PROPAGATION

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.