中低速冲击下Ⅰ型裂纹的动态断裂韧度研究

Dynamic toughness of mode Ⅰ crack under medium and low speed impacts

起裂韧度和扩展韧度是分别用来判别裂纹起裂和扩展的两个重要材料参数,为了探索在中低速冲击荷载下岩石的起裂韧度和扩展韧度的测试方法,选择砂岩单裂纹半圆孔板试样以中低速落锤试验机进行了冲击,并利用裂纹扩展计和应变片测试裂纹的起裂时间及裂纹扩展速度。使用AUTODYN有限差分软件,裂纹软化模型及线性状态方程建立了相应的数值计算模型,结合实验-数值法确定预制裂纹的起裂韧度和扩展韧度,结果表明:动态冲击载荷下裂纹扩展速度不是一个常数;对于隆昌青砂岩,其动态扩展韧度与裂纹扩展速度成反比关系,扩展速度越大,扩展韧度越小;材料扩展韧度不是一个独立的材料参数,而是一个与裂纹扩展速度有关的参数。

Initiation toughness and propagation toughness are two important material parameters used to describe crack state.In order to study the rock dynamic initiation toughness and propagation toughness of mode Ⅰ crack under medium and low speed impacts,an experimental study was performed by using single cleavage semi-circle compression(SCSC) specimen and a drop weight testing system.The crack initiation time and the propagation characteristic were measured by strain gauges or crack propagation gauge(CPG).By using crack softening(CS) model and linear equation of state,numerical models were established by using finite difference AUTODYN code.The experimental-numerical method was used to determine crack initiation toughness and propagation toughness. The results show that: Under impact loads,crack propagation speed is not a constant; Propagation toughness is inversely proportional to the crack propagation speed for the Longchang green sandstone; Propagation toughness is a not independent material parameter,but is related to crack propagation speed.