On The Mechanism Of The Dynamic Fracture Processes Of Rock Under Impulse Loading

The thesis has systematically investigated the mechanism of dynamic fracture processes of rock subjected to impact loads. The dynamic characteristics and responses of the rock fracture processes have been analyzed from micro, meso and macro levels respectively. The thesis includes the following work.1. Three typical stress waves induced by impact loads were analyzed by both Fast Fourier Transform (FFT) and Wavelet, and the distribution rules of frequency and energy of stress waves were obtained. According to the trait of the impact loading, the paper proposed that the size relation between the wavelength of stress waves induced by impact loads, faults in rock and the samples may be used for the classification criterion among the micro, meso and macro dimensions.2. The dynamic fracture processes of rock under impact loading are regarded as adiabatic or quasi-adiabatic processes in micro thermodynamics. Associated with the state equation of rock subjected to impact loading, the constitutive relation of rock suitable for this situation was obtained, and the breakage condition of micro thermodynamics for rock under the impact loading was proposed.3. The stress field near the crack subjected to impact loads was investigated. The main factors, which have effect on dynamic stress intensity factor (DSIF), are the size of the stress releasing zone and the distribution of the stress out of the release zone. The calculation formula of DSIF was proposed. The dynamic responses of crack subjected several typical impact stresses such as shear, normal and oblique incident stress waves were simulated. According to the results of the simulation the DSIFs were calculated. The angle of initiation of the crack was predicted. The method ofoptimizing fracture generating by stress pulses was discussed.4. The propagation characteristics of the stress waves transmitting to the weak interface or opened crack was investigated systematically. For its limitation, the energy criterion under the sliding condition for one point was generalized to the whole interface by inducting the dissipating energy value to indicate the possibility of slide. This method was verified by the stress criterion; The geometry of opened crack and its physical property have effect on the propagation of stress waves according to analytical results; The deformations of reflected stress waves recorded in the SHPB tests were investigated emphatically, and the process of the change of the reflected stress waves refers to the process of dynamic damage cumulation or the dynamic fracture.5. Based upon the study on rock responses to impact load by the principles of energy dissipations and associating with the damage mechanics and the action density of the stress waves as well, the dynamic cumulative damage formula of rock under dynamic cyclic loading at the damage phase was proposed. According to the fractal phenomenon analysis on rock fragments, the iterative relationship expression about the damage fractal value and the number of the fragments of rock subjecting to impact load was obtained. At the same time, the iterative relationship expression about the damage fractal value and the impact energy was proposed basing on the principles of energy dissipations and the criteria of dynamic brittle fracture. The results of tests show that the relation among the impact energy, the damage of rock and the number of fragments lies in a state of mutual coupling.