After more than 30 years of development, Computational Weld Mechanics (CWM) has made a tremendous progress. The objective of this thesis is to focus on the development of more accurate algorithms that capture more physics while requiring less computer time.; Due to the limited capacity (speed and memory) of computers, simulation of large complex welding structures is usually not satisfactory. This thesis aims at computing physical changes in long welds, especially during the quasi-steady state period.; In this work, a weld pool model is proposed to compute the surface geometry of the molten pool as well as a temperature distribution in the weld pool region. The temperature field in the weld joint is computed by solving a convective-diffusion heat equation, based upon the space-time finite element method which can deal with both transient and steady state. The model for evolution of microstructures in low-alloy steels is implemented for both an Eulerian formulation and a Lagrangian formulation. The results from the microstructure analysis, such as specific volume and phase fractions, can be used in stress analysis to capture the effects of volume change during phase change on the stress states. In thermal-stress analysis, a flow tube model, which possesses features from both the Lagrangian formulation and the Eulerian formulation, is developed to predict the steady-state stress and displacement fields in the weld joint domain. A thermal-elasto-viscoplastic constitutive relationship, with consideration of transformation plasticity, is applied.; All these analyses are coupled by data flows to incorporate interactions between the thermal, mechanical and metallurgical processes present in the welds. The input data for the analysis included geometry, material properties, initial temperature field, initial microstructure states, base metal and filler metal compositions, initial stress and strain states, and boundary conditions appropriate for the problem analyzed. Numerical results are compared with experimental, analytic or other numerical results.
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