PROGRESSIVE FAILURE CHARACTERISTICS AND ENERGY EVOLUTION OF GRANITE IN BRAZILIAN DISC TESTS

Previous research of Brazilian disc test and simulation is mostly focused on either macroscopic failure modes or micro evolution rules. The energy evolution characteristics in the splitting process remains to be discussed in detail. In this paper,Brazilian disc tests are carried out on granite. The fracture processes of specimens are monitored using digital image correlation (DIC) and acoustic emission (AE). Both fracture modes and scales during the test are analyzed. On this basis,PFC^2D is employed to simulate the process of Brazilian disc test. The energy characteristics of specimen is illustrated by comparing different energy components. The test and simulation results indicate that: (1) The process of Brazilian disc test is divided into four stages,including fracture compaction (Ⅰ),cracks initiation (Ⅱ),cracks growth (Ⅲ) and post-peaking failure (Ⅳ)stage. (2) Tensile microcrack is the major fracture mode in both stage Ⅱ and Ⅲ. Shear microcrack occurs at later period of stage Ⅲ. Then macrocrack forms in the loading diameter direction,and causes the final failure. (3) There is nearly no dissipated energy in first two stages. All the external work is transformed into releasable strain energy in the specimen. At the end of stage Ⅲ,the strain energy releases rapidly,and the energy of AE reaches to the maximum as the stress approaches to the peak. The releasable strain energy decreases remarkably at stage Ⅳ. The portion of dissipated energy increases significantly due to a large number of new fracture surfaces are formed.