Computational weld mechanics

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The proposed research is to solve for the design of welded structures, i.e., we no longer assume the design is given. Instead we assume that we are given in-service loads and a preliminary design with no weld joints specified. The analysis should predict the optimum position and size of all weld joints, weld procedures, weld schedules, fixture design and fixture schedule.  For an important class of welded structures, the primary failure mode is fatigue.  Given CAD files for the geometry of the parts for a structure such as a large tractor, the material type for each part and the associated in-service loads, we propose the following strategy:  Mesh all parts automatically. Then the user applies in-service loads and constraints. Then with constraints between adjacent parts applied automatically perform a linear static (or dynamic) 3D FEM analysis.   Also potential weld paths are identified automatically by adjacency between parts.  From the constraint force per unit length along each potential weld path, a trial weld size and weld procedure will be computed.  Next the structure is remeshed to include the proposed weld joints with filler metal.  Then a thermal stress analysis of the weld joints in the welded structure is done to compute the transient temperatures, microstructure evolution, residual stress and distortion due to welding.  The weld pool size and shape will be computed using an Ohji-Sudnik weld pool model. Microstructure evolution will be modelled using Monte Carlo algorithms and computational thermodynamics. The stress analysis will include single crystal thermo-visco-plastic analysis of the evolving microstructure.  Then either a linear or a non-linear plastic FEM analysis with constraints is redone with the new weld joints.  In these weld joints, the 3D stress distribution due to in-service loads and residual stress in the weld joints and particularly in high risk features such as the weld toe are computed.  From the stress distribution and in-service load cycles, the fatigue life of the weld is estimated. If the fatigue life is too long, the weld size can be reduced. If the fatigue life is too short, the weld must be strengthened or redesigned. This process will be done automatically.