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

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 center dot m(1/2), as the loading rate is about 4.0 x 104 MPa center dot 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.