爆炸载荷作用下不同长度裂纹的动态扩展规律研究

Study on dynamic propagation law of cracks with different lengths under blasting

为研究爆炸载荷作用下砂岩材料中不同长度裂纹的动态扩展规律,借助裂纹扩展计(crack propagation gauge)测试砂岩中裂纹的起裂规律、裂纹扩展速度等,将试验中测得的岩石动力学参数以及裂纹扩展时刻等数据导入有限元软件ABAQUS建立数值计算模型,通过试验-数值法得出不同长度裂纹的裂纹扩展速度、动态应力强度因子以及砂岩的断裂韧度等参数。试验结果表明:(1)爆炸试验中,不同长度预制裂纹的起裂时间与延迟断裂时间不同,预制裂纹长度在60~80 mm时,起裂时间与延迟断裂时间变化不明显,80~120 mm时基本呈线性增长,之后变化趋于平缓;(2)砂岩的动态裂纹扩展速度不是一个定值,在扩展过程中有起伏变化,预制裂纹长度对于动态裂纹的平均扩展速度的影响较小,不同裂纹长度的平均扩展速度的变化范围在10%左右;(3)随着预制裂纹长度的增加,砂岩的起裂韧度逐渐增加,即砂岩开裂难度增加,其扩展韧度与扩展速度成反比关系,这种反比关系在裂纹长度变化时依然成立。

In order to study the dynamic propagation law of cracks with different lengths in sandstone materials under blasting loads,the crack initiation law and crack propagation speed of sandstone are studied with the help of crack propagation gauge.The dynamic parameters of sandstone and crack propagation time measured in the test are imported into ABAQUS code,a finite element software,to establish a numerical calculation model.The crack propagation speed and dynamic stress intensity factor of mode I cracks and fracture toughness of sandstone with different crack lengths are obtained by experiment-numerical method.The test results show that:(1)In the blasting tests,the initiation time and delayed fracture time of pre-cracks with different lengths are different.When the lengths of pre-cracks vary between 60 and 80 mm,the change of initiation time and delayed fracture time is not obvious,and it basically increases linearly when the lengths vary between 80 and 120 mm,and then the change tends to be flat;(2)The dynamic propagation speed of crack in sandstone is not a not a constant value and fluctuates during crack propagation,when the lengths of pre-cracks vary between 60 and 140 mm,the pre-crack length has little effect on the average propagation speed of dynamic crack,and the variation range is within 10%;(3)With the increase of pre-crack length,the initiation toughness of sandstone increases gradually,that is,the difficulty of sandstone initiation increases,and its propagation toughness is inversely proportional to the propagation speed,which is still valid when the crack length changes.