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基于Kaiser效应由裂纹扩展释放弹性波产生的认识,依据断裂力学理论就加载方向变化对Kaiser效应的影响进行分析。研究了远场应力为拉应力时,二维Ⅰ,Ⅱ型混合裂纹扩展的临界应力相对值、FR比值与加载方向偏转角之间的关系。结果表明:加载方向对Kaiser效应点反应岩石记忆先期荷载值的准确度有较大影响,其变化大小与临界应力相对值正相关。若第一次加载方向与裂纹面垂直,偏转角度从0°~90°变化,裂纹扩展临界应力相对值和FR比值均不断增大。偏转角为0°~20°时,FR比值变化范围为1~1.1,Kaiser效应点记忆较为准确,但第二方向所记忆的荷载并非该方向的正应力值。偏转角为90°时,临界应力相对值和FR比值均趋近于无穷大,裂纹在该裂纹面方向上不能发展,说明Kaiser效应消失。这与部分学者的试验结果一致,说明此类劈裂试验中Kaiser效应的产生,裂纹扩展是主要原因,也在某种程度上解释了该类试验加载方向偏转角度越大,Kaiser效应越来越不明显的问题。
Based on the knowledge of Kaiser effect that the crack propagates to release elastic wave, the influence of the change of loading direction on the Kaiser effect is analyzed based on fracture mechanics theory. The relationship between the critical stress, the ratio of FR and the deflection angle of loading direction is investigated when the far-field stress is tensile stress. The results show that the loading direction has a great influence on the accuracy of Kaiser effect point reaction rock memory preload value, and the change of loading direction is positively correlated with the relative critical stress value. If the first loading direction is perpendicular to the crack plane, the deflection angle changes from 0 ° to 90 °, the relative values of the crack propagation critical stress and the FR ratio increase continuously. When the deflection angle is 0 ° ~ 20 °, the FR ratio changes from 1 to 1.1. The Kaiser effect point memory is more accurate, but the load in the second direction is not the normal stress value in this direction. When the deflection angle is 90 °, the relative value of critical stress and FR ratio approach infinity, and the crack can not develop in the direction of the crack surface, indicating that the Kaiser effect disappears. This is in line with the experimental results of some scholars, which shows that the Kaiser effect and crack propagation are the main reasons for such splitting tests. To some extent, Kaiser effect is getting bigger as the loading angle of the test is larger Obvious problem.