压剪条件下预埋椭圆裂纹三维扩展实验研究

EXPERIMENTAL STUDY ON THREE-DIMENSIONAL (3-D) PROPAGATION FROM A PRE-EXISTING ELLIPSE FLAW UNDER COMPRESSION-SHEARING

本文首先试制了透明的低温树脂材料和非透明的砂浆类材料.然后,通过实验研究了这两种材料内置椭圆形裂隙的三维始裂、扩展过程及其破裂过程中声发射信号特征,并采用三维断裂理论确定了内部裂纹的三维始裂状态.实验结果表明,在单轴压缩荷载作用下,两种材料中内置裂隙初期破裂面形态基本一致,均为一对反对称的包裹状翼裂纹,但初始起裂位置有所不同.透明树脂试样中,初始的新生裂纹几乎在预制裂纹长轴端部附近同时起裂,但起裂点并不在裂隙长轴端部,而在砂浆类材料内的起裂位置则靠近短轴端部,亦不在短轴端部.相同条件下,两种材料的最终破裂状态明显不同,透明树脂试样是以宏观劈拉破裂为主,而砂浆类试样则以宏观剪切破裂为主,这可能与材料性质和三维裂隙的起裂位置不同有关.本文的三维断裂分析结果与实验一致.

Some testing samples with a pre-existing ellipse flaw （b/a=0. 5） are made from two selffabricated non-transparent mortar and transparent resin materials. Under uniaxial compression, a series of observation experiments on the 3-D fracture process of the flaw are carried out. The experimental results show that the primary crack shapes are basically similar in the two different materials, namely a pairs of antisymmetric wrapping wing cracks; however, their initial fractured places are different. In the transparent resin specimens, some new cracks initiated almost simultaneously near the tips of the long-axis of ellipse flaw than at its tips. However, in the non-transparent mortar specimens, some new cracks initiated near the tips of the short-axis of ellipse flaw than at its tips. At the same condition,ultimate fracture patterns of two materials are markedly different. In the transparent resin specimens,the macroscopic tensile fracture mode is dominant; however,in the non-transparent mortar specimens,the compression-shearing fracture mode is dominant. This is believed to be closely related to the material behavior and the initial location of three-dimensional crack. In this contribution, the three-dimensional fracture analysis is carried out, with good agreement with the experiments.