Computational weld mechanics

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In many in-situ weld repairs in thermal and nuclear power plants, petro-chemical and tar sands plants, the application of an elevated temperature post-weld heat treatment to reduce the hardness of the weld to acceptable levels is difficult and/or expensive. In those circumstances, the ASME Boiler and Pressure Vessel Code recommends the `half-bead' weld technique in which half of the filler metal deposited in each weld pass is removed by grinding before applying the next weld pass. A properly designed temper bead weld procedure can eliminate the very expensive grinding step of the half-bead weld technique. Performing the tests needed to qualifying a temper bead weld procedure can be expensive. The first objective of this proposal is to develop a computational model to automate the design of an optimal temper bead weld procedure for a given weld repair problem. The model will compute the transient temperatures and the evolution of the microstructure during welding and final hardness distribution for essentially all feasible variations of the welding process and then choose the optimal design and report the performance. The intent is to try to reduce the number of tests required to qualify the procedure to one. A second objective of this proposal is to automate the design of welding procedures to minimize the risk of hot cracking in welding austenitic stainless steels that are susceptible to hot cracking. Hot cracking in welds is a serious limitation in welding many stainless steel alloys used in applications that must resist corrosion and/or high temperatures. We propose to develop a holistic 3D transient model of hot cracking in welds that will couple our existing transient thermal analysis using an Ohji weld pool model with our existing synthetic microstructure evolution (but will add a phase field model with segregation and solute diffusion) with our existing transient thermo-visco-elasto-plastic stress and strain and strain-rate distribution model. It will also add single crystal plasticity. These models will reduce costs and improve the quality and reliability of welded structures.