Laser Cladding Ti/ha Composite Thermo-mechanical Coupled Analysis And Numerical Simulation

In this dissertation, thermo-mechanical finite element analysis on laser cladding of Ti/HA is presented. Optimum process parameters are obtained, including scanning velocity, powder flow velocity, laser intensity, overlapping rate. Based on temperature and residual field analysis, cracking region and direction are predicted. Furthermore, a number of feasible approaches are proposed for the purpose of eliminating or depressing residual stress. The validity has been confirmed sufficiently in simulation.The time dependent temperature field caused by moving Gauss distributing heat source are numerically calculated for the laser cladding of single-path and multi-paths. In 3D model, material failure of HA, the temperature dependent material properties, enthalpy of material and various boundary conditions including radiation, convection and density of heat flow rate are taken into account. Based on hypothesis that the cross section of coat is half-ellipse and the temperature of coat boundary matches well with melting point, the real coat profile is obtained by dimension modifying and iterative algorithm, Using Hierarchical Parameterized Finite Element Approach, optimum process parameters are obtained, which include laser intensity, scanning velocity and powder flow velocity. The results match well with the actual experiment. The contributions of this research do not only create a accurate 3D finite element model, but also provide a computational technique for optimization of a laser cladding process.According to the temperature field of multi-paths with consideration of melting pool's interface flatness, the temperature field was discussed in three cases of overlapping rate and the optimum overlapping rate was achieved. The numerical results show the validity of the present method.There are two mainly factors to influence the thermal stress due to forming. One is temperature gradient, the other is mismatch in material properties between coating and substrate. Based on thermo-mechanical coupling method, the thermal stress due to mismatch in material properties and temperature gradient is analyzed in detail respectively. The numerical results show that, on interface between coating and substrate, mismatch in material properties only leads to shear stress with largest values at model center. The residual stress distribution of single layer is also calculated and the reasonable explanation was drawn. Based on residual stress field analysis, crack propagation region and direction are predicted. Eventually, a number of feasible approaches are proposed for the purpose of eliminating or depressing residual stress.