【作者】 宋惠珍； 袁岩光；

【Author】 Song Huizhen Yuan Yanguang (Inatitute Of Geology,State Seismological Bureau)

【机构】 国家地震局地质研究所；

【摘要】 本文介绍了用裂纹扩展模型计算的雁列裂纹应力场及势剪破裂区,裂纹模型可以反映出由于裂纹离面的摩擦滑动和尖端张破裂扩张导致变形局部化,计算采用平面应力有限单元模型,岩石的弹性模量E=10¹¹Pa,泊松比v=0。25,裂纹离面的摩擦系数μ=0.6,裂纹面与第一坐标变量轴重合,在远场边界上施加分布荷载,σ₂=5σ₁,随着荷载逐步增加,雁列裂纹的两相向尖端首先发生张破裂,然后两反向外尖端也发生张破裂,计算输出了破裂过程的各阶段结果。计算表明:对左旋左阶梯的雁列裂纹,当裂纹面开始滑动但相向两尖端发生张破裂之前,由于相向内尖端的张破裂扩张,加速了反向外尖端的张破裂扩张,而与此同时,相应的势剪破裂区在外尖端张破裂扩张的反方向上形成,并占据优势。更多还原

【Abstract】 The finite element technique of fracture mechanics is used for computing the echelon crack stress field and zones of potential shear fracturing.The localization of deformation caused by the frictional slip of crack and extensions of tensile fracturing near crack tips can be revealed by the crack model.The computational method used is the finite element technique of plane-stress.Far-field stresses are chosen so thatσ₂=5σ₁,and the maximum compressionσ₂ is 30°from the X direction.The elastic constant E and v are 10¹¹ Pa and 0.25,respectively. There are three contact states on the crack surfaces during deformation of slot,namely〔1〕They stick each other when the normal and shear component of displacement are equal to zero.〔2〕They open each other when the normal component of traction F_n and the shear component F_t are positive constant.〔3〕They are specified to follow a linear friction law,in which the coefficient of frictionμ=0.6 when the normal component of displacements is equal to zero and the shear component of traction F_t satisfies the inequality Ft_>0.We treat triangular quarter-point elements as elastic crack tip with anomaly of stress field near the crack tip. The computation shows: For left-lateral shear,left step echelon crack,before extensions of tensile fracture at inner tips of echelon crack modeⅡstress intensity is 1.331 at inner tip and 1.266 at outward tip of right half-length of crack.For left-length of crack, modeⅡstress intensity is 1.330 at inner tip and 1.256 at outward tip of left half-length of crack.Therefore,at first extensions of tensile fracturing occur at inner tips of echelon crack,then left half-length crack is connected with right half-length one.After that,modeⅡstress intensity increases to 1,477 at outward tip of right half-length and 1.468 at outward tip of left half-length.The results indicate that extensions of tensile fracturing at inner tips will facilitate tensile fracture at outward tips of echelon crack.At the same time,there appears to have two zones of potential shear fracturing,one of them is in the direction to opposite to that of the previous tensile fracture.Another is consistent with the X direction.After extension of tensile fracture at outward tip of crack zones of potential shear fracturing are dominant.更多还原