各向同性材料中微裂纹的最大屏蔽效应

通过对微裂纹屏蔽不同来源的分析及计算，发现在各向同性脆性材料中，残余应力释放引起的微裂纹对主裂尖产生最大屏蔽效应时该微裂纹的倾角与最大张应力的方向没有明显的对应关系．在Hutchinson[1]所指出的屏蔽效应的第二个来源中，还应计及微裂纹形成引起的远场应力在微裂纹处产生的应力场的释放从而导致应力场的再分布．

MAXIMAL COCK TIP SHIELDING BY MICROCRACKING IN ISOTROPIC ELASTIC SOLIDS

In Hutchinson's (1987) opinion, there are two sources of microcrack shielding, one is the reduction in the effective elastic moduli resulting from microcracking and the other is the strain arising from the release of residual stresses when micro-cracks are formed. This residual stresses in question develop in the fabrication of polycrystalline or multi-phase materials due to thermal mismatches between phases or thermal anisotropies of the single crystals. In this paper, besides the two sources of the redistribution of stresses in the near-tip stress field of the macroscopic crack,the third source of microcrat shielding was proposed, i.e., the redistribution of stresses in the near tip induced by far field stresses while microcracking. That is to say, the microcrack could relieve the far field stresses and produce strains, this trains are different with the strains produced by the residual stresses motioned by Hutchinson, it could be noted as release of induced stresses. The influence of these three sources on shielding and anti-shielding effect of the main macrocrack due to near-tip microcracking is discussed.When considering the reduction in the effective elastic moduli resulting from microcracking and the strains produced due to release of induced stresses, the shielding and anti-shielding effect of the main macrocrack due to near-tip microcracking is then evaluated. It is concluded that: the oriedations of microcrack don't normalized to the direction of maximal tension stress when the maximum shielding effect occurs in the point under investigation. This result is different from the conclusion derived by Ortiz (1989) in isotropic brittle solids.