异种钢焊接接头残余应力理论预测的基础问题研究

The fundamental issues on how to accurately predict welding residual stress distribution in typical weld joints used in nuclear power plants will be investigated by means of experiment and numerical simulation technology in this project. Through designing reasonable experimental methods, we will measure the temperature-dependent mechanical properties, parameters related to solid-state phase transformation and "annealing effect temperature". These measured data will be directly used in the new numerical simulation method developed by this work. To increase the computing efficiency, a new heat source model named "variable length heat source" will be proposed. Meanwhile, based on conventional thermo-elastic-plastic finite element method, an advanced material model considering work hardening rule, annealing effect and solid-state phase transformation will be developed to accurately simulate welding residual stress in similar and dissimilar metal weld joints with thick plates. Using the measured data and the developed computational approach, we will clarify the influence of yield strength, work hardening, annealing effect and solid-state phase transformation on welding residual stress distribution. Through comparing the simulation results with the residual stress values measured by experimental mock-ups time after time, we will verify the computational approach. The ultimate objective of this project is to establish a thermal-metallurgical-mechanical finite element method with high accuracy and high efficiency for predicting welding residual stress. The new computational approach not only is an effective tool for evaluating the structural integrity and security, but also is helpful to make reasonable welding procedures and optimize the design of weld joints.

以核电设备中典型结构材料奥氏体不锈钢、镍合金和低合金高强钢的焊接接头为研究对象，采用物理实验与数值模拟技术相结合的方法，对焊接残余应力理论预测的若干基础问题进行深入研究。一方面通过设计合理的实验方案，测量母材和焊缝金属的高温力学性能、固态相变相关参数和退火效应温度等，为数值模拟提供准确的材料数据。另一方面开发可变长度热源模型以及考虑加工硬化、退火效应和固态相变的先进材料模型来高效、高精度地模拟厚大焊接接头的残余应力。利用实验测量的材料数据和所开发的数值模拟方法，澄清材料的屈服强度、加工硬化、退火效应及固态相变等对焊接残余应力的影响。本项目的目标是通过数值模拟结果与实验的反复比较和验证，最终确立预测焊接残余应力的高效、高精度热-冶金-力学耦合的有限元计算方法。该数值模拟方法将是核电设备中关键焊接接头结构完整性和使用寿命评价的有效工具，同时它也能用于指导制定合理的焊接工艺和优化焊接接头设计。

本项目的主要目标是开发高精度材料模型和高效计算方法来模拟各种焊接接头的残余应力。在本研究中，重点研究了几种核电和火电等高端装备中的异种钢焊接接头的残余应力的分布特征以及在建筑钢结构中的一些典型厚大焊接接头和结构的焊接残余应力分布特征。取得的主要研究成果包括：1）基于实验测量和数据收集，初步建立了包括奥氏体不锈钢、镍基合金和低合金高强度钢在内的数种典型结构材料的温度依存的热物理和力学性能数据库，为准确计算这些材料的焊接残余应力奠定了基础。2）开发了固态相变材料模型来高精度地模拟如P91/P92等材料的焊接残余应力。同时，采用数值Satoh实验澄清了固态相变在焊接残余应力形成过程中所起的作用。3）开发焊后热处理计算方法，研究了焊后热处理对P91钢焊接残余应力的影响。4）澄清了加工硬化准则和退火软化效应对奥氏体不锈钢和镍基合金的焊接残余应力计算精度的影响，针对工程实际应用，在平衡实用性与计算精度的条件下，推荐了简便材料模型。5）针对厚大焊接接头，在考虑结构和材料特点的前提下，提出了高效的热源模型来模拟焊接残余应力。6）详细研究了SUS304/Q345异种钢接头的焊接残余应分布特点。7）开发高精度的材料模型，数值模拟了P92/SUS304异种钢多层多道焊接接头的残余应力。基于数值模拟结果详细分析了焊接残余应力的分布特征。8）采用本研究开发的数值模拟方法计算了核电中几种典型异材焊接接头的残余应力。.本研究取得的成果使采用数值模拟方法高精度地预测复杂形状、厚大形状和异种钢焊接接头的残余应力成为了可能。项目取得的研究成果不仅实质性地推动了计算焊接力学学科的发展，本项目开发的数值计算方法也具备较高工程应用价值，这些计算方法可以直接用于如核电、火电等高端装备中典型焊接接头的残余应力的理论预测。