动载确定方法对岩石动态断裂韧度测试的影响

Influence of different dynamic load calculating methods on rock dynamic fracture toughness test

为了考察不同方法确定的动态载荷对测试岩石动态断裂韧度的影响,在SHPB压杆系统上动态冲击直径80 mm的大理岩圆孔裂缝平台巴西圆盘,获得了弹性压杆上的应力波形,间接计算得到3种不同的作用在圆盘端部的动态载荷。将载荷输入ANSYS动态有限元模型中,求得了相应的动态应力强度因子,并根据试验-数值分析方法确定了岩石的动态断裂韧度测试值。结果表明,在加载速率约为4.0×104MPa·m1/2/s的条件下,采用三波法确定的大理岩的平均动态断裂韧度为3.92 MPa·m1/2,采用一波法比三波法计算的结果偏低11.22%,采用二波法比三波法计算的结果偏高20.15%,3种方法得到的结果差异较大。应力波在传播过程中,通过圆盘表面和预制裂缝面发生散射,部分能量不断发生释放是造成圆盘试件两端加载载荷不相等的主要原因。三波法是3种方法中比较理想的动态载荷确定方法,但需要考察试件的动态应力平衡性。

To investigate the influence of testing rock dynamic fracture toughness by dynamic load calculated using different methods, some holed-crack flattened Brazilian disc specimens （HCFBD） with diameter of 80 mm are impacted in SHPB system. The stress waveforms in the elastic compression bar are got, and the dynamic loads applied on the disc are calculated indirectly using three kinds of methods. When the different loads are inputted in ANSYS dynamic finite element mode, the dynamic stress intensity factors could be made, and the corresponding test values of dynamic rock fracture toughness are got on the base of experimental--numerical method. Results show that the average dynamic fracture toughness of marble is 3.92 MPa· m^1/2, as the loading rate is about 4.0×104 MPa· m^1/2/s. Compared with the test value by ＂three wave method＂, it is 11.22% less by ＂one waves method＂; and 20.15% more by ＂two waves method＂. So, the results are very different using three methods. The dynamic loads on both ends of disc specimen are not equal, because part of energy is released continually when the stress waves scatter through the surfaces and the prefabricated crack of the disc specimen in the whole transmission process. ＂Three waves method＂ is a relatively ideal one to determine the dynamic load on the disc specimen in three methods, but the dynamic stress balance should be surveyed.