爆炸荷载作用下青砂岩Ⅰ型裂纹动态扩展规律及动态断裂参数研究

Dynamic propagation law and dynamic fracture parameters of mode Ⅰ crack in sandstone under blasting

为了研究爆炸荷载下岩石Ⅰ型裂纹的动态起裂和扩展的规律以及其扩展过程中有关的动态断裂参数,提出了带切槽的半圆加矩形SREN(Semicircle and Rectangle with Edge Notches)板试件,试验材料为青砂岩,只采用雷管起爆作为动力源,通过3种不同长度的预制裂纹,结合裂纹扩展计(Crack Propagation Gauge,CPG)测速系统,获得裂纹的起裂和扩展时刻,求得了扩展速度并运用分形理论对其进行修正。同时,考虑到岩石为典型的脆性材料且裂纹尖端附近断裂区域为小变形,以及炸药在爆炸过程中压力和密度之间的关系,在AUTODYN软件的数值模拟研究中,岩石材料采用Linear状态方程、Elastic强度准则和Principal Stress失效模型,炸药材料采用JWL状态方程,通过模拟可观测裂纹扩展路径并检验试件的合理性。运用位移外推法,使用有限元软件ABAQUS计算了裂纹起裂及扩展时的应力强度因子,结合CPG测得的断裂时刻,获得了每种试件构型在不同扩展长度下的动态断裂韧度。通过实验并结合数值模拟结果表明:使用的大尺寸SREN试件能有效地减少反射拉伸应力波对裂纹动态起裂及扩展的影响,可作为脆性材料动态断裂参数测量的试件;随着预制裂纹长度的增加,起裂时间变长,平均扩展速度变小且波动变小,趋于稳定扩展;预制裂纹长度的增加,也会导致起裂韧度测试值逐渐减小,扩展韧度测试值并非定值,会大于起裂韧度测试值并逐渐减小。

In order to study the law of crack initiation and propagation of mode Ⅰ crack in rock under blasting and the related dynamic fracture parameters during the propagation process,the SREN(Semicircle and rectangle with edge notches)specimens made of sand-stone with pre-crack and detonators were used for explosion experiments.In the experiment,three different lengths of pre-crack and crack propagation gauge(CPG)velocity measurement system were used to obtain crack initiation and propagation time,and the propagation velocity was obtained and corrected by fractal theory.This paper also used the AUTODYN code to carry out numerical simulation.Considering that rock was a typical brittle material and the fracture area near the crack tip was small deformation,the rock material adopted linear equation of state,elastic strength criterion,principal stress failure model and the JWL equation of state is used for the explosive material to describe the relationship between pressure and density during the explosion process.The simulation results can be used to observe the crack propagation path and verify the rationality of the new specimen.Using the displacement extrapolation method,the stress intensity factor of crack initiation and propagation was calculated by finite element software ABAQUS.Combined with the fracture time measured by CPG,the dynamic fracture toughness of each specimen under different extension lengths was obtained.By using the above experiment combined with numerical simulation,the results show that the large-sized SREN specimen used in this paper can be less affected by the reflected tensile stress wave,and applied to the measurement of dynamic fracture parameters of brittle materials.With the increase of the pre-crack length,the crack initiation time becomes longer,the propagation average velocity becomes smaller and the fluctuation becomes more stable.The increase of the pre-crack length will also lead to the decrease of crack initiation toughness.The propagation toughness is not fixed and will be greater than the cracking toughness and gradually decrease.