焊接过程材料硬化行为表征及应力应变演化

A proper material hardening model, which can accurately describe the thermo-elasto-plastic stress-strain relationship, and the strain-stress evolution model during welding are important to predict welding residual stresses and assess the integrity of welded structure accurately, which has important scientific value and real significance.. The background is the welding residual stress assessment of main pipe in the nuclear reactor pressure vessel. In this program, 316L austenitic stainless steel was selected. Amethod was proposed to modify the welding heat source mode based on the cross-section profile of molten pool, temperature curve and cooling rate, which can accurately simulate welding thermal process. A-F non-linear kinematic hardening model was modified and the relationship between parameters and temperature was deduced. Combined with a certain proportion isotropic hardening model, a new non-linear mixed hardening model was erected. The reliability and necessity of the non-linear mixed hardening model were validated based on isothermal tension and compression test, Satoh test, a single bead weld and mutipass welding of 316L stainless steel. Combined the welding numerical simulation and DIC dynamic strain measurement approach, considering the Annealing effect, a new thermo-elasto-plastic strain-stress evolution model was proposed based on of Radaj’s model.

建立合适的材料硬化模型，准确表征焊接过程材料的硬化行为和应力应变演化过程，对准确地预测焊接残余应力、评估焊接结构完整性具有重要的科学价值和现实意义。本项目以核反应堆压力容器主管道焊接残余应力评估为背景，以316L奥氏体不锈钢为研究对象，提出以熔池横截面形貌、温度曲线及焊接冷却速率修正焊接热源模型，实现焊接温度场的准确模拟；改进A-F非线性随动硬化模型，推导模型参数与温度之间的关系，结合一定比例的等向硬化模型，建立一种新的非线性混合硬化模型；基于等温拉伸压缩试验、Satoh试验及316L不锈钢表面堆焊、多道焊试验，验证非线性混合硬化模型的可靠性。结合焊接数值模拟和DIC动态应变测量，基于拉达伊应力应变演化模型，考虑材料退火效应，提出新的焊接过程准稳态下热弹塑性应力应变演化模型。

为了实现焊接过程的精准模拟，设计了多级载荷等温循环拉压试验方法，提出相对内应力评价材料循环载荷下的硬化行为，建立了非线性混合硬化模型，表征焊接过程材料的应力应变演化行为；基于等温拉压试验、Satoh试验及数值模拟，通过非线性混合硬化模型、等向硬化模型和随动硬化模型的敏感性分析，验证了非线性混合硬化模型的准确性；提出了高温非弹性应变处理方法，建立了力学熔点测试方法，结合非线性硬化模型和力学熔点，建立了材料的连续体本构模型；以Peclet系数判定熔池液态金属的热传输主导方式，结合焊缝熔池横截面形貌，建立了复杂焊接热源模型，以焊接温度曲线及焊接冷却速度，验证焊接热源模型的准确性；开展了平板表面堆焊、多道焊试验及焊接数值模拟，计算的焊接残余应力与实测值比较，研究了硬化模型和力学熔点对焊接残余应力的影响，进一步验证了非线性混合硬化模型的可靠性，上述研究内容成功地应用于不锈钢激光焊的数值模拟；开展了深孔法和数字图像相关法的研究，搭建了两种方法的测试平台，并且成功地应用于焊接残余应力的测试，为焊接残余应力的测试提供了新的手段；基于拉达伊应力应变模型，考虑力学熔点，提出了新的焊接过程热弹塑性应力应变演化模型。. 本项目实现了焊接过程材料力学本构模型的精准建模，提出新的焊接过程热弹塑性应力应变演化模型，对焊接力学和数值模拟的发展及应用具有重大的推动作用和研究意义。