Computational weld mechanics

在许多热电厂和核电站、石化厂和沥青砂厂的现场焊接修复中，采用焊后高温热处理将焊缝硬度降低到可接受的水平是困难的和/或昂贵的。在这种情况下，ASME锅炉和压力容器规范建议采用“半道焊”焊接技术，即在应用下一道焊道之前，通过打磨去除每个焊道中沉积的填充金属的一半。设计合理的回火堆焊工艺可以消除半堆焊技术中非常昂贵的打磨步骤。进行合格的回火堆焊程序所需的测试费用可能会很高。该建议的第一个目标是开发一个计算模型，以自动设计给定焊接修复问题的最佳回火堆焊程序。该模型将计算焊接过程中的瞬时温度和组织演变，以及焊接过程中几乎所有可行的焊接过程的最终硬度分布，然后选择最佳设计并报告性能。其目的是试图将合格程序所需的测试次数减少到一次。这项建议的第二个目标是自动化焊接程序的设计，以最大限度地减少焊接易受热裂影响的奥氏体不锈钢时出现热裂的风险。在焊接许多必须耐腐蚀和/或耐高温的应用中使用的不锈钢合金时，焊缝的热裂纹是一个严重的限制。我们建议开发一个完整的焊接热裂纹三维暂态模型，该模型将我们现有的使用Ohji熔池模型的暂态热分析与我们现有的综合组织演变(但将增加一个具有偏析和溶质扩散的相场模型)与我们现有的暂态热粘弹塑性应力、应变和应变率分布模型相结合。它还将增加单晶的可塑性。这些模型将降低成本，提高焊接结构的质量和可靠性。

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.