动载下两条断续预制裂隙贯通机制研究

采用预制断续裂隙类砂岩模型试样单轴动载试验，对不同裂隙空间位置（雁行、共面排列）条件下两条裂隙的贯通机制进行了研究。静、动荷载下的对比研究成果显示：不同窄间位置的裂隙贯通方式存在较大差异，且对动载的响应不同：动载下分支裂纹扩展及贯通具有惯性效应，即动载下裂尖翼裂纹及次生兆面裂纹起裂后易朝原起裂方向快速发展，动载下易在两预制裂隙内端部产生直接贯通。这与静载下岩桥处的贯通常通过分支裂纹拐折扩展、相连不同，这也是导致裂隙试样中低应变速率下强度增大（即速率效应）的主要原因。同时，试验结果也揭示：动载下次生共面裂纹扩展长度增加、预制裂隙尖端易产生直接贯通是地震荷载下易发生宏观Ⅱ型剪切断裂的又一原因。

MECHANISM OF FRACTURE COALESCENCE BETWEEN TWO PRE-EXISTING FLAWS UNDER DYNAMIC LOADING

The mechanism of the fracture coalescence between two flaws is studied under uniaxial dynamic loading.The specimens made of sandstone-like modeling material contain two pre-existing flaws with different geometry distribution including echelon and co-planar arrangement pattern.Through the comparisons of the fracture propagation length,coalescence mode of the fractures and strength increase of the pre-cracked specimens under static and dynamic loading,the dynamic response of the fracture coalescence is found different from static one under different geometric setting of the flaws.Furthermore,the inertia effect of the fracture propagation is revealed under dynamic loading,the growth of the wing fracture and secondary co-planar fracture tends to the original propagation directiona;nd the immediate coalescence is taken place easily between two pre-existing flaws.But the fracture coalescence path is winding under static loading,which is different from dynamic loading.So,the inertia effect of the fracture propagation is regarded as the main cause of the strength increase of the brittle material under slow to medium strain rate.In virtue of the explanation,the second cause of the mode II shear fracture under earthquake is released.