Study On Material Point Method For Shock Initiation Of Solid Explosive

Study on initiation kinetics is very important for military science. Due to its complexity, progress of experimental and theoretical study is very slow. With the rapid development of computer technology, more and more attention was paid on numerical simulation.The main work of this paper focused on Shock to Detonation Transition (SDT). SDT problems, involving large deformation, chemical kinetics, multiphase coupling and so on, is solved difficultly by traditional grid-based algorithms, such as the finite element method (FEM) and the finite difference method (FDM). For the Lagrangian grids, large deformation will lead to large distortion, it made the time steps became smaller and smaller, which made the whole calculation time extended. And mesh distortion made the accumulated error increscent. For the Eulerian grids,there are advection errors. To overcome these disadvantages of traditional grid-based algorithms, meshfree methods were developed rapidly and became hotspot in Computational Mechanics. The material point method (MPM) is an extension to solid mechanics problems of a hydrodynamics code called FLIP which, in turn, evolved from the particle-in-cell method. MPM, which is a new meshfree method, takes advantage of both Eurlerian and Lagrangian methods and avoids the mesh distortion and tangling issues associated with Lagrangian methods and the advection errors associated with Eulerian methods. The key feature of the MPM is the use of the same set of nodal basis functions for both the mapping from material points to cell nodes, and the mapping from cell nodes to material points. As a result, the use of the single-valued mapping functions yields a natural no-slip contact/impact scheme so that no interpenetration would occur for penetration problems.Impact dynamics model with material point method was established, and explicit calculation format of MPM was deduced. Fixed background mesh was used, and finite element shape function was used for function approximation. Stress for large deformation material which exhibit elastic-plastic behavior was integrated by Jaumann stress rate. Artificial bulk viscosity was used to treat shock wave. For the stability of explicit time integration, the time step and sound speed was studied. Several impacting problems were computed. Several impacting problems with different strength models were computed, and it shows that Strength model has little effect on the calculation results. MPM method, FEM method, SPH method were used to simulate impact engineering problems, and the comparison of results proved the advantage of MPM from the aspect of precision and cost. At last, a hypervelocity impact problem was study. The shapes of debris cloud obtained by MPM are in agreement with the experimental result.Material point method was first proposed for SDT problems. JWL Equation of state was used for unreacted explosive and reacted product, and ignition and growth model of explosive initiation was used. According to thermodynamic equilibrium assumption in material points, a two-phase mixture of unreacted explosive and reacted product was proposed. And multi-material material point, which contains unreacted explosive and reacted product in the same time, design procedure was first proposed on that basis. Because of rapid process of explosive detonation, the mass fraction incremental of combustion was controlled to promote accuracy. Simulating some SDT problems, the critical detonating velocities were gained by means of the'up-down'method. Compared with the traditional algorithm, the superiority of material point method in the calculation of shock initiation problems is obvious.Duration and value of shock wave in explosive generated due to impact was deduced with shock wave theory. And a method in engineering calculation, which was validated by numerical results, was proposed in this paper. Engineering calculation method and numerical simulation methods complement each other.Currently, the material point method is still in the research stage, and there is no commercial software. A Computer code was developed, which provide a new numerical simulation platform for impact problem and SDT problem. It contains pre-processing, main calculation and data interface modules, and Tecplot, Origin software can be used for Post-processing.