裂纹非一致起裂对动态断裂韧度确定的影响

为了考察中心圆孔裂缝平台巴西圆盘试件直裂缝非一致性起裂对测试岩石动态断裂韧度带来的影响,在霍普金森压杆冲击系统上对圆盘试件进行冲击试验,获得了端部加载载荷和裂纹前缘不同点的起裂时刻,并借助ANSYS动态有限元分析得到了圆盘试件三维裂纹前缘不同点的动态应力强度因子时间历程曲线,采用实验—数值方法计算得到相应的动态断裂韧度值。结果表明:裂纹前缘点对应动态应力强度因子值沿厚度方向逐渐递增;二维分析方法得到的动态应力强度因子与三维分析方法裂纹前缘中心处的值最为接近,两者的相对误差小于5%,对应确定的动态断裂韧度值相对误差小于1.2%。如果不考虑圆盘厚度影响,假设试件在圆盘表面起裂,由裂纹前缘其它点所求得的动态断裂韧度值与二维方法得到的值相对误差最大可以达到23%,采用二维简化方法存在较大的误差。

Influence of Determining Rock Dynamic Fracture Toughness by Disc Specimens with Inconsistent Crack Fracture

In order to investigate the influence of the method to determine the rock dynamic fracture toughness by holed crack flatted Brazilian disc with inconsistent straight crack fracture. In the split Hopkinson press bar system, the disc specimens were subjected to impact, the dynamic load between two load ends were applied, and the initiation time of different point on the crack front was got. Meanwhile, using ANASYS software, the three-dimensional finite element models of disc specimen were set up, the time history curves of dynamic stress intensity factor at different points on the three-dimensional crack front were analyzed. The corresponding dynamic fracture toughness was calculated by experimental - numerical methods. The results show that, the dynamic stress intensity factor value of the crack front increase along the thick direction gradually. The factor of the crack front center point is most close to the value calculated according to plane state assumption, the relative error between them is less than 5 percent, and the relative error of the dynamic fracture is less than 1.2 percent. However, when the impact of the disc thickness is not considered, and assuming the crack point just being located on the surface of the disk, the relative error between the values obtained from other points of the crack front and the two-dimensional method can reach 23 percent. There are great errors in using a two-dimensional simplified method.