Simulation-Based Research On Crack Propagation Mechanism Of Rock-Like Materials Under Dynamic Stress

With the development of high-rise buildings and underground projects, more attentions have been paid to the dynamic properties of bedrock structures in both theoretical studies and engineering applications. As a heterogeneous material, when the stress is higher than the strength of rock, instantaneous energy release results in stress redistribution, which triggers dramatic deterioration of rock mechanical properties and rapid propagation of cracks. Under the combined effect of heterogeneity and internal stresses in the rock material, crack propaga-tion is essentially featured by crack curving and branching. Therefore, crack growth in rock-like materials subjected to dynamic loading, especially crack curving and branching, is one of the theoretical and engineering problems attracting attentions of many researchers.In this study, the dynamic version of RFPA2D(Realistic Failure Process Analysis) pro-gram was employed to simulate crack propagation. The research content was as follows:1. Since the Weibull distribution of the properties of mesoscopic structures and the linear mesoscopic mechanical behaviors can reflect the macroscopic nonlinear behaviors, a constitutive model for damage evolution was developed to simulate the completely fail-ure process of rock subjected to dynamic stress. By importing the Viscous-spring artifi-cial boundary into the model, the wave propagation in heterogeneous infinite media was investigated.2. Based on dynamic method and the linear mesoscopic mechanical behaviors can reflect the macroscopic nonlinear behaviors, the collision process between two heterogeneous spe-cimens was researched in details. Because the interaction between the impactor and spe-cimen was considered, the model was closer to the reality. Three typical impact models were investigated in the paper. Comparing with the former experimental results, the availability of the method was verified. Furthermore, the different degree of heterogenity was also discussed in details. The reasearch can enrich and extend the former investiga-tion.3. Based on damage theory and FEM method, rock fragmentation mechanism induced by a drill bit subjected to dynamic loading was investigated. Compared with rock fragment by static stress, there is a stress transition from compression to tension in the specimens un-der dynamic loading, e.g. the compression stress will be changed to tension during wave propagation. The results show that the process of wave propagation is changed and the emergency of tension is the key of crack initiation and growth.4. By numerical method, the asymmetric and discontinuous behavior of crack propagation was analyzed at mesoscopic scale based on the damage evolution principle. The results coincide with the experimental laws, so it is certain that the linear mesoscopic mechanical behaviors can reflect the macroscopic nonlinear behaviors, and the complex mechanism of crack propagaion at macroscopic scale can be analyzed by this way.