The SPH Method And Its Application In Hypervelocity Impact

Smoothed Particle Hydrodynamics (SPH), as a meshless method, has been widely applied to computational mechanics. Compared with the traditional finite element method (FEM) or finite difference method (FDM), SPH has its unique advantages in the simulation of hypervelocity impact in which large deformation always occurs. In this thesis the theoretical basis and discretization method of SPH are described. The adaptive method and partition/coupling method of SPH are discussed with the aim to improve the computational efficiency and accuracy. Several corrections and improvements are proposed to make the method more suitable for the computation of various impact dynamics problems. The study of the practical application of the method such as spallation and high velocity impact computations is also carried out. The results show that SPH has good performance in the numerical study of impact dynamics and good value in the engineering application.First, kernel estimate and particle approximation of a function and its derivatives are obtained by kernel interpolation theory and the discretization formulations for conservation equations in continuum mechanics are developed. In addition, several issues, such as kernel function, smoothing length, neighbor particle search and constitution relations are discussed. The flowchart of computations for the SPH method is also outlined.The propagation and reflection of one dimensional strain waves induced by planar impact are simulated by means of corrected smoothed particle method (CSPM) and good results compared with the analytical solution are obtained. The spallation experiments of Al-Li alloy are also numerical simulated by inserting the constitutive equation and damage evolution equation into the program. The free surface velocity curve obtained by the computation is well suited with the experiment results. It's shown that the accuracy of CSPM in the computation of the movement of free surface is sufficient to describe the phenomenon of dynamic fracture.Then the adaptive SPH method is proposed. In the computation of one dimensional stress wave, an adaptive SPH method which can automatically insert particles in the wavefront and delete particles after wave is developed, and it can improve the accuracy of the computation effectively. In the two dimensional hypervelocity impact simulations, another adaptive SPH method which can automatically insert and merge particles based on the particle distance is also proposed. The new method is demonstrated to suppress the numerical fracture effectively and improve the computational accuracy of the program greatly.In order to improve the efficiency of the SPH method, the partition method of SPH is developed. In the method, the entire computational domain is divided into several regions, in the regions where large deformation may occur more particles are placed, while in other regions only fewer particles are placed. The partition method not only ensures the computational accuracy, but also improves the computational efficiency. A method is proposed to solve the computation problem near the partition interface, and a more efficient particle search algorithm is also developed.Finally, the study of the engineering applications of the FEM/SPH coupling method is carried out. The contact and sliding algorithms between elements and particles are modified. Numerical simulations for the penetration of ceramic composite target by long-rod projectile are performed by inserting the constitutive models of the ceramic and metals into the program. The computational results are in good agreement with the experiments, and the effectiveness of the method and constitutive models are verified. The coupling method is shown to have good practical value and it will have bright future in the impact dynamics computations.