Research On Dynamic Damage Characteristics Of Rock Under Impact Load

The dynamic damage mechanics character of rock under impact loading is always on the focus of rock mechanics research. In the last few decades, Some scholars have achieved a series of result of the fields of rock dynamic characteristic, constructive relation model and calculation of numerical simulation, but there are still many problems unsolved. The text simply reviewed the findings and shortages about rock-material dynamic mechanic behavior on the aspects of experimental and theoretical research. The questions about it are be researched On the side of one-dimensional stress and the other side of one-dimensional strain. At the same time, the dynamic damage model of rock under impact loading is also researched in the result of experiment and theory analysis. The following is the content and the result.(1) The equipment of a split Hopkinson pressure bar(SHPB) is utilized in the dynamic impact loading experiment of one-dimension stress. The test result indicates that both compression strength and the young's modulus are strain rate-sensitivity, but the initial tangent modulus is strain rate-insensitivity, they are also affected by the test equipments and the mode of loading in a certain extent. The young's modulus increased obviously with growing-up impact speed. The whole material represents as a size harden effect. A little variety of strain rate can increase compression strength obviously. The cause of damnification breakage is the side direction stretch.(2)The research of dynamic mechanics experiment of one-dimension strain condition is investigated by single-stage-gun. The rock materials which accorded with engineering background is simulated as the ground stress conditions by the active confining pressure. The experiments of planner impact were performed to the rocks material included confining pressure and non-confining pressure with the speed of 200-400m/s, and Manganin gauges between the rock targets were used to record the stress-time curves at the different locations of target. With the measured stress histories, the complete histories of strain, strain rate, specific volume, density and particle velocity are gained by using path line principle of Lagrange Analysis. The results indicate that rock and confining pressure rock have some similar response behavior in some respects, such as the rate-sensitivity, the dispersion and attenuation effect of pressure pulse, and the stagnant-return and flow-deformation phenomena of stress-strain curves and so on, but the confining pressure decrease the nonlinear of stress-strain curves. Confining pressure can also raise the shock resistance ability, the stiffness and ductility of rock targets.(3) Based on the analysis of damage mechanism and failure model for material, a dynamic damage constitutive model is constructed to describe the constitutive response of rock material. The model is described briefly as the following hypothesis:1) Rock is assumed in a macroscopic view as homogenous continuum with a mass of stochastically distributed micro-damage; 2) Damage evolution is considered to be the accumulation of micro-crack growth due to the interior tension stress, which leads to a decrease of strength and stiffness of rock; 3) Compaction of rock is essence a collapse of the material voids, which produces the plastic strain and the increasing of the bulk modulus in the rock, so this process is considered as the evolution development of void damage; 4) When crack density reaches a critical value, the rock material destroy tack place. The comparison of model curves and experimental curves indicate that this model can describe the constitutive properties excellently.(4)Base on the point of composite material mechanics, the confining pressure rock is considered as a enhanced composite material, a dynamic constitutive equation which is suitable for engineering analysis is briefly proposed. The equation include in two aspects: 1) The effect of confining pressure on constitutive property is characterized by the damage evolution equation; 2) The mutation of mechanics parameters in the dynamic impact process is described by stress relaxation time.(5) Adopting VISC2D and VISC3D, the dynamic collision process of rock target impacted by flyer are simulated, and the dynamic failure mechanism is analyzed excellently.