Numerical Simulation Of Welding Residual Stress Relieving By Hammer Peening

Hammer peening is a kind of very effective process relieving welding residual stress, which has many unique advantages, and was applied widely in engineering. However, the research of hammer peening cannot far meet its applications in practice. On the basis of the large commercially available finite element ANSYS code, the numerical simulation method was applied to study primarily the process of relieving welding residual stress by hammer peening in this paper.Based on thermal elastic-plastic theory the simulation of welding stress strain field was carried out in this paper, and the finite element model was established with contact element on the basis of contact theory, the contact mechanical behavior and the effect of hammer peening were calculated and analysed. Finally, the parametric simulation program was designed with ANSYS APDL language, various simulation of welding and hammer peening can be analysed through defining different parameters.The three-dimensional finite element model of plate surfacing was established. The sequential coupled method was introduced to calculate the effect of thermo-mechanical coupling. Gauss distributed surface heat source was employed to simulate welding arc, the loading of moving heat source was achieved by applying heat flux on solid element surface. The varying material's physical property parameters with temperature changing were taken into account, and the high temperature material physical property parameters were properly selected and adjusted. The uneven grid of meshes was used, the grids of meshes were very fine in the region of weld and its vicinity, but the grids were quite coarse in other region far away weld.As for the high-complicated nonlinear problem of welding thermo-mechanical analysis, a series of nonlinear measures were taken to strengthen solution convergence and accurate result. Automatic time stepping, line search and predictor were adopted, full Newton-Raphson procedure was applied to solve interactively in stress-strain field simulation, moreover, changing time-step method was introduced to improve thecomputation speed. Finally, the calculation result was analysed and verified well with experiment.In the numerical simulation of relieving residual stress by hammer peening, contact element technique was firstly adopted for establishing the finite model and calculating the hammer peening. The interfaces between hammer and plate were discretized by contact element that overlay on base solid element surface. Augmented Lagrangian method was specified calculating normal contact force, Coulomb friction law was specified calculating tangent contact force. On computation small time-step and the real constant values of contact element such as FKN, FTOLN etc must be specified correctly for ensuring convergence and accurateness.The fall-ball impact test and its calculation demonstrated that impact force is changed as approximate sinusoid with contact time. Maximum contact pressure is located at the contact center, it decreases with the increment of distance from contact center. When impact energy reaches a certain value, the impact action can produce compressive residual stress in the region of contact surface. With impact energy increasing, impact force increases correspondingly, but contact time decreases and contact region enlarges.The hammer peening simulation showed that tensile residual stress at the center location of peening center decreases sharply by hammer peening once. In a certain range of impact energy, with impact energy increasing, the effect of relieving residual stress enhances. When the value of impact energy is constant, with the hammer curvature radius increasing, the valid scope enlarges correspondingly, nevertheless, the effect of relieving residual stress declines.