高强低合金钢焊接过程多物理场耦合数值模拟

目前高强低合金钢焊接数值模拟中，采用热-力耦合分析时，忽略固态相变效应，残余应力模拟值与试验测量值误差较大。为提高焊接数值模拟精度，根据多场耦合关系，基于传热学、固态相变理论和连续介质力学，建立焊接过程多物理场耦合本构方程，并通过子程序将其嵌入到通用隐式有限元程序中。采用数值模拟与试验分析的方法研究高强低合金钢小试样的自由膨胀试验、相变塑性试验及平板焊接试验应力及各应变分量的演变。研究结果表明：固态相变体积变化引起的相变应变对残余应力有显著影响，不但改变了残余应力的大小，甚至改变了残余应力的符号，考虑相变塑性应变时会降低应力的水平。残余应力改变程度与相变程度有关系：完全相变区影响最大，部分相变区次之，未发生相变区最小。相变应变和相变塑性应变最终大小相当。研究方法为深入了解高强低合金钢焊接过程和焊接工艺优化提供了理论基础。

Numerical Simulation of Multi-physical Coupling of Welding Process for High Strength Low Alloy Steel

At present, the errors between welding residual stress simulation results and experimental measurements are large for high strength low alloy steel when adopting coupled temperature-displacement analysis and omitting solid-state phase transformation effect. Based on the multi-physical coupling relationships, a multi-physical coupling constitute equation is established by using heat transfer, solid-state phase transformation theory and continuum mechanics to improve welding numerical simulation accuracy and then the equation is implemented into the general purpose implicit finite element program via user material subroutine. The evolution of stress and strain components of free dilation test, transformation induced plasticity test and flat plate welding test are investigated by means of both numerical simulations and experiments. The results suggest that transformation strain caused by volume change has significant effect on welding residual stress, which not only changes the magnitude of residual stress and even changes the sign of residual stress. Transformation induced plasticity strain lowers the magnitude of residual stress. The extent of welding residual stress change has a close relationship with the degree of phase transformation, fully-transformed region is larger than partially-transformed region, and partially-transformed region is larger than untransformed region. The final transformation strain is approximate to transformation induced plasticity strain. The presented research method provides a theoretical basis for deeper understanding of welding process and optimization of welding technology.