Numerical Study On Dynamic Fracture Behavior Of Rock Materials Under Compression Based On General Particle Dynamics

Rock is a kind of heterogeneous medium, which is composed of one or more minerals. Under the external load, the meso crack initiates, develops, connects and coalesces, and eventually leads to the fracture of the rock. The results of the tests, such as stress, strain and rupture mode, are often the macroscopic reflection after the cumulative rupture. Numerical simulation methods can be used to analyze the failure mechanism of the specimens from the two aspects of the micro crack development and the macro mechanical behavior, thus becomes the focus of the research in the field of geotechnical engineering.Meshless particle method can completely or partly eliminate the finite element grid which is the base of the numerical simulation methods as finite element methods, and displays unique advantages in the numerical simulation of large deformation, dynamic fracture, impact load and fissile materials. In this paper, the general particle dynamics method is developed to study the crack propagation of the cuboid rock specimens under different loading speed combined with confining pressure. The main research work is as follows :(1) GPD simulation program which is used to analyse the three-dimensional crack expansion of the cuboid rock specimens is based on three control equation as the conservation of mass, momentum and energy in the continuum mechanics, combines the constitutive equation of rock solid mechanics and follows the discretization and kernel function idea in the Smoothed Particle Hydrodynamics method. The pre-processing program and post-processing program are also be developed to image the text data.(2) By comparing the numerial results, we find that the model size has a very important influence of the failure mode of the cuboid rock specimen under uniaxial compression at intermedium strain rate, while the the cracking stress and peak stress of mechanical parameters is less affected. The crack in the long and thin rock specimen developes along the directions of principal stress, in the form of split failure. While in shorter rock specimen, there is a vertical crack and an oblique crack across through the specimen.(3) Contrast results on non-homogeneous cuboid rock specimen at different loading rate show that dynamic uniaxial compressive strength and strain rate relationship function is consistent with the empirical formula of the test. The peak strain increase greatly with strain rate increase, while the young's modulus increases smaller.At the same strain rate, the sample with higher homogeneity coefficient has higher compressive strength and larger peak strain. The failure mode changes with the strain rate. At a high strain rate, more vertical cracks appears and the horizontal crack's expansion speed becomes faster, resulting in the specimen broken into smaller size block.(4) A variety of three axis simulation tests are designed at different strain rates and confining pressure to analyse the combined effects. It was found that the crack stress, strain and dynamic compressive strength and peak strain of rock increases with the increase of confining pressure. The dynamic Triaxial compressive strength at different strain rate is represented by Mohr-Coulomb formula and compared with the experimental results. The amplitude of the dynamic triaxial compressive strength decreases with the increase of confining pressure.