压剪作用下单一闭合裂纹起裂扩展研究

Study on initiation and propagation of a single closed crackunder compression-shear stress

构建了压剪作用下单一闭合裂纹尖端应力场方程,应用最大周向应力准则分析了翼裂纹开裂角,侧压系数k对应力场和翼裂纹起裂扩展的影响,单轴压缩下裂纹倾角α对翼裂纹起裂应力的影响。通过单轴压缩试验及三轴文献数据对比验证了理论解的正确性。研究表明:开裂临界相对尺寸λ→0或裂纹倾角α→45°,T应力对翼裂纹开裂角的影响作用可以忽略;周向拉应力随侧压系数k的升高而降低,翼裂纹起裂所需轴向应力增大;围压对翼裂纹的扩展存在抑制作用,且裂纹面有效剪应力大于0时抑制作用更强;试验观察到预制裂纹尖端出现翼裂纹和少量的反翼裂纹和共面剪切裂纹,翼裂纹的开裂角在预测值附近上下波动;单轴压缩,翼裂纹起裂应力随裂纹倾角的增大而增大;三轴压缩,翼裂纹起裂应力随侧压系数的增大而增大,与模型预测的变化关系具有一致性。

Field equation of single and closed flaw tip under compression-shear stress is constructed in this paper.The initiation angle of wing crack,the influence of side pressure coefficient k on stress field and initiation and propagation of wing crack and the influence of flaw angleαon initiation stress of wing crack under uniaxial compression are analyzed by using the maximum tangential stress criterion.The correctness of the theoretical solution is verified by uniaxial compression test and triaxial compression literature data comparison.The research shows that the effect of T-stress on the initiation angle of wing crack can be ignored when the critical relative size of crackingλapproaches 0 or the flaw angleαapproaches 45°.Hoop tensile stress decreases with the increase of side pressure coefficient k,and axial stress required for the initiation of wing crack increases.The confining pressure has an inhibitory effect on the propagation of wing cracks and the inhibitory effect is stronger when effective shear stress of the flaw surface is greater than 0.Wing cracks and a small number of anti-wing cracks and coplanar shear cracks are observed at the tip of the pre-existing flaw.The initiation angle of wing cracks are fluctuated around the predicted value.The initiation stress of wing crack increases with the increase of flaw angle under uniaxial compression,and it also increases with the increase of side pressure coefficient under triaxial compression,and they are consistent with the changing relationship predicted by the model in this paper.