A Study Of Abrasive Particle Acceleration Process And Material-Removal Mechanism In Abrasive Waterjet Machining By SPH Coupled FEM

Numerical simulation is applied in this thesis to study the mixing and acceleration process between abrasive particle and high pressure waterjet in a cutting head in Abrasive Waterjet Cutting (AWJC). And when the particle ejects the nozzle and impacts on the target, micro-cutting material removal mechanisms are also studied. With the difficulty of the fluid-solid interaction and extremely large deformation problem using finite element method (FEM) or using the ALE method which reduced the automaticity of the program and made the computation expensive, we develop the SPH coupled FEM modeling for abrasive waterjet machining simulation is presented in order to overcome the above difficulties.Using this method, the acceleration process of single abrasive particle in a nozzle is investigated in the first section. High-speed water jet is built using SPH elements, while abrasive particle and nozzle are modeled in FEM. In order to couple SPH and FEM as well as realize the interaction between abrasive particle and waterjet, contact algorithm is included using LS-DYNA. In the computer simulation, evolution of abrasive and waterjet velocities along focus tube is analyzed; trajectory of abrasive particle in focus tube is sighted; the relationships between abrasive particle velocities and different water pressures are described; the rule of outlet velocities of abrasive particle vs. dimensionless ratio of diameter is conducted. The current model is validated by the existing theoretical and experimental data. Orthogonal Test and Analysis of Variance (ANOVA) are both used to investigate the significance of three different factors (abrasive diameter, water pressure and focus diameter) to the outlet velocity of abrasive particle.In the second section, micro-cutting material removal mechanisms caused by different shape of abrasive particles are studied and computational model is established. The spherical and angular particles are adopted to simulate the ploughing and cutting deformation in metallic material and the particle is still modeled using FEM method. Though Lagrangian finite element (FE) methods have been found to be appropriate to model the impact of small spherical particles on relatively hard materials, ploughing deformation and cutting deformation may lead to distorted and tangled elements that result from the very large plastic deformations induced in the target. Therefore, traditional Lagrangian FE methods are not suitable for the modeling of angular particle impacts on ductile materials and Smoothed particle hydrodynamics (SPH) which is a meshless method may have significant advantages over FE methods for the simulation of angular particle impacts is applied in this study. Spherical and angular particles impact the target in different angles and velocities. Previous experimentation and the simulation results are compared to demonstrate the credibility of the simulation results.According to the entire computer model, including nozzle, abrasive particle, high pressure water and different shapes of particle as well as the target, that will be benefit to understand the abrasive waterjet cutting mechanism and optimize the operating parameters.