动载荷作用下含倒U型孔洞裂纹试件的动力损伤行为研究

裂纹群对隧道围岩的动力学特性影响机制复杂程度远大于单裂纹缺陷。为了研究裂纹群对隧道围岩破坏行为的影响机制,采用PMMA制备含倒U型孔洞裂纹模型试样模拟含裂纹缺陷围岩工况,利用落锤冲击试验机进行动态加载,分析遭受冲击载荷作用下裂纹群在围岩内的损伤演化规律,随后采用有限差分法软件进行数值分析,对比论证试验结果的科学性,及分析在冲击载荷作用下裂纹群对围岩应力状态的影响,结果表明:(1)裂纹群对裂纹的扩展速度有显著地促进作用,多裂纹试件的裂纹扩展速度是单裂纹试件的1.277倍,且多裂纹试件的裂纹起裂时间明显缩短;(2)相对于单裂纹缺陷试件而言,多裂纹试件的动态断裂韧度明显降低,为单裂纹的58.72%;(3)多裂纹试件内I/II复合裂纹的起裂明显易于纯I型裂纹,且动态断裂韧度与II型动态应力强度因子有很大关系。

Study on fracture properties of specimens with inverted U-shaped hole and cracks under dynamic loading

The influence of crack group on the dynamic mechanical characteristics of surrounding rock is more complex than that of one single-crack.To deeply understanding dynamic failure properties of cracks in surrounding rock mass,several inverted U-shaped model samples with one single-crack or multi-cracks were made of polymethyl methacrylate(PMMA),and then two sets of impact tests were carried out by using a drop hammer impact testing device to evaluate dynamic fracture behavior under impact loads.The corresponding numerical simulation was performed by employing a modified version of the finite difference method code and a traditional version of the finite element method code.The effects of one single-crack or multi-cracks on crack propagation velocity,dynamic fracture-initiation time and dynamic fracture-initiation toughness under impact loads were discussed,and comparison between experimental and simulation results was carried out.Some significant conclusions were obtained:(1)multi-cracks have an increasing influence on the crack propagation velocity,the crack propagation velocity of a multi-cracks specimen is 1.277 times than that of one single-crack specimen and the dynamic fracture-initiation time decreases with the number of cracks.(2)Compared with the single crack specimen,the dynamic fracture-initiation toughness of the multi-cracks specimen is significantly reduced to 58.72%of that of the single crack specimen.(3)The failure of mixed mode I/II crack is obviously easier than that of pure mode I crack in a same multi-cracks sample and the dynamic fracture-initiation toughness is closely related to the mode II dynamic stress intensity factor.