Finite Element Analysis Of Thermal Effect In Electron Beam Welding Of Thick Titanium Alloy

The results of thermal effect during electron beam welding of thick titanium alloys are simulated using ANSYS software. In this dissertation, a three-dimensional finite element model and a composite source model composed of Gaussian surface source and rotational paraboloidal body heat source have been established to simulate the temperature fields and stress fields respectively during lower focus and upper focus electron beam welding in 20mm thick flat plate of TA15 titanium alloy.The results of temperature fields show that the simulated peak temperature in the weld pool during lower focus electron beam welding is 3200℃,while upper focus is 2700℃. During upper focus electron beam welding, the whole superficial temperature is higher than that of lower focus electron beam welding, while the whole inner temperature is lower than that of lower focus. The simulated thermal cycling curves are well consistent to the results tested by thermocouple. And there is a good consistency between the simulated weld pool and the real weld shape.Based on the results of temperature fields and thermal elastic-plasticity theory, indirect coupling method is employed to compute the development histories of thermal elastoplastic stress during welding process, as well as the distribution of residual stress after welding. The simulated results show that the stress of weld zone changes from compressive stress to tensile stress during the moving of electron beam. The residual stress of weld developed in these two welding methods is mainly compression stress. Overall, the value of the residual stress is nearly equal between lower focus and upper focus. Both of the longitudinal residual stress and transverse residual stress decrease when the distance increases from the weld center. Then the residual stress changes from tensile stress into compressive stress at the edge of the workpiece. The longitudinal residual stress and transverse residual stress are measured by the hole drilling method. The distribution and changed trends are consistent to the tested results.