带微裂纹物体的有效断裂韧性

按照等效介质的思想，引进有效表面能密度的概念，建立了带微裂纹物体有效断裂韧性的公式．具体计算了微裂纹群分别平行和垂直于宏观裂纹两种情况的减韧比．表明微裂纹群在产生应力屏蔽（或反屏蔽）效应的同时，也降低了材料的有效断裂韧性，减小了对宏观裂纹的扩展阻力．

THE EFFECTIVE FRACTURE TOUGHNESS OF MICROCRACKED BODIES 1)

The driving force for the propagation of the macrocrack is reduced by the microcrack zone around the crack tip region of the macrocrack,meanwhile, damage is occurred in the macrocrack tip region, in which the materials is weakened by microcrack damage. Then the fracture toughness of the materials in the macrocrack tip region is decreased. The evaluation of the effect of the microcrack damage on the mechanical behavior must take into account both the stress-shield effect and the decreasing effect of the fracture toughness of the materials in the macrocrack tip region. In this paper the effect of microcrack damage on the fracture toughness of the materials are quantitatively investigated. By considering the microcracked solid as an effective medium and introducing the concept of effective surface energy density,we derive the formula for the effective fracture toughness of a microcracked body. As an application,the toughness-reduction ratios are given in the case that all the microcracks are normal to the macrocrack and the case that all the microcracks are parallel to the macrocrack,respectively. It is shown that the shielding effect functions in the above two cases and the toughness-reduction effect of distributed microcrack are remarkable.