孔洞对爆生裂纹动态扩展行为影响研究

试验研究含有预制裂纹的砂岩圆板在爆炸荷载下不同孔洞间距(S)对裂纹动态扩展行为的影响。试验中采用应变片测试获取爆炸加载波形作为AUTODYN数值模拟裂纹扩展效果及ABAQUS数值计算应力强度因子的加载力。试验中采用CPG测得裂纹起裂—扩展时刻,根据测得试验数据得出普适函数,对ABAQUS计算所得应力强度因子进行修正最终得到裂纹动态极限应力强度因子。通过对比分析在不同孔间距下裂纹的动态极限应力强度因子,裂纹扩展长度及裂纹扩展速度得出以下述结论:(1)孔洞对爆炸荷载下的预制裂纹动态扩展行为有所影响,且孔洞间距越小其影响效果越显著;(2)一般情况下裂纹的起裂极限应力强度因子要略高于扩展极限应力强度因子,裂纹的扩展速度对裂纹扩展极限应力强度因子有一定影响,且二者总体趋势呈反比;(3)当裂纹扩展至孔洞附近时,由于孔洞的作用提高了裂纹的扩展极限应力强度因子,进而降低了裂纹的扩展速度并减小了裂纹的扩展长度。此外若将孔洞视为隧道光面爆破中的辅助孔或周边孔,那么研究结论可为隧道光面爆破中控制断面内的原生裂纹扩展长度,以期达到隧道围岩最大程度上的完整性提供理论支撑。

Influences of holes on dynamic propagation behaviors of blasting cracks

The influences of different spacings of holes on the pre-crack propagation behaviors of circular sand specimens under blasting loads are investigated. The explosive loading waveform from experiments is obtained as the loading stress of AUTODYN to simulate the crack propagation, and it is embedded in ABAQUS once more to calculate the stress intensity factor (SIF) of the static cracks under dynamic loads. The initiation-propagation time of pre-crack is measured by using CPG in the experiments. According to the CPG data to obtain the universal function, the dynamic initiation-propagation critical SIF is yielded by modifying the static SIF obtained from ABAQUS using the universal function. By comparing and analyzing the dynamic critical SIF, crack propagation velocity and length of crack propagation under different spacings of holes, we can obtain the following conclusions: (1) The holes have an effect on the dynamic propagation behaviors of cracks under blasting loads, and the smaller the spacing, the more remarkable the effect. (2) In general, the crack initiation critical SIF is higher than the propagation one, and the crack propagation velocity has influences on SIF, and their overall trends are inversely propotional. (3) The critical propagation SIF of cracks increases due to the action of the holes when they propagate near the holes, both of whose propagation length and velocity are reduced. In addition, if we take the holes as the auxiliary or surrounding ones in tunnel smooth blasting, the conclusions of this study will provide theoretical support for controlling the crack propagation length to achieve the integrity of surrounding rock.