基于DSI/DIC技术的异种钢焊接接头非均匀疲劳力学行为与损伤演化研究

Welding of dissimilar metals has been increasingly applied into the manufacture of advanced equipments. In this project, aiming at such prominent problems as remarkable heterogeneities of microstructures and properties as well as complicated distributions of the residual stress at weld joints of dissimilar metals, both mechanical behavior and damage evolution in localized areas, including welding metal, fusion zone, heat affect zone, parent metal, etc., at weld joints of dissimilar steels with two typical forms of welding line are investigated by combing depth-sensing indentation (DSI) technique with digital image correlation (DIC) technique under typical fatigue loadings. Based on DSI measurements, the heterogeneous distribution characters of mechanical properties, including strength, stiffness, plasticity and toughness, and residual stresses at weld joints of the dissimilar steels as well as their correlations with the applied stresses and fatigue cycles are studied. Based on DIC measurements, the heterogeneous elastoplastic deformation fields at weld joints during fatigue process as well as their effect on the changes in mechanical properties and residual stresses in localized zones of weld joints are studied as well. In terms of the degradation of mechanical properties and elastoplastic deformation behavior in weld zones during fatigue process, the characterization of fatigue damage, the damage constitutive equation, the damage evolution law, etc. are further studied in the framework of the continuum damage mechanics (CDM). A new approach for applying to evaluating the fatigue strength of weld joints of dissimilar metals will be explored. It is thus of important theoretical and engineering practical significance.

异种金属焊接在先进装备制造中应用日趋广泛。本项目针对异种金属焊接接头具有显著组织与性能非均匀性以及复杂残余应力分布等突出问题，将深度敏感压痕（DSI）技术与数字图象相关（DIC）技术相结合，来研究典型疲劳加载下两种典型焊缝形式的异种钢焊接接头局域（包括焊缝、熔合区和热影响区及母材等）非均匀力学行为与损伤演化。基于接头区DSI测试，研究疲劳过程中焊接接头各局域力学特性（强度、刚度、塑性和韧性）与残余应力的非均匀分布特征及其与作用应力、疲劳循环的相关性。基于接头区DIC测试，研究疲劳过程中焊接接头各局域非均匀弹塑性变形场及其对接头局域力学性能变化与残余应力动态演化的影响。依据疲劳过程中焊接接头局域力学性能劣化与弹塑性变形行为，采用连续损伤力学方法研究异种钢焊接接头的疲劳损伤表征、损伤本构方程与损伤演化律等问题。探索适用于异种金属焊接接头疲劳评定的新途径，因此，具有重要的理论和工程实际意义。

异种金属焊接在先进装备制造中应用日趋广泛。本项目针对异种金属焊接接头具有显著组织与性能非均匀以及复杂残余应力分布等突出问题，将深度敏感压痕（DSI）技术与数值图像相关（DIC）技术相结合，研究典型疲劳加载下异种金属焊接接头局域（包括焊缝、熔合区和热影响区及母材等）非均匀力学行为与损伤演化。首先采用弹塑性有限元数值模拟，针对宽范围工程应用材料（约700个算例），对迄今国内外提出的基于压痕法测试残余应力的代表性模型（共12种）进行了在不同拉、压残余应力下的预测精度比较，得出修正Suresh模型具有较高的综合预测精度。采用上述残余应力模型对HR3C /T92异种金属焊接接头在焊态和退火态下进行深度敏感压痕测试，获得了焊接态接头局域残余应力的分布特征。采用化学腐蚀与电解腐蚀相结合，成功制备出适用于不锈钢/耐热钢焊接接头不同区域多尺度变形测试的金相散斑。并利用该散斑对目前用于DIC分析的主要算法进行了对比验证。结果表明，不同算法的计算结果较为接近，而优选相关性参数（子区大小、ROI尺寸等）是提高计算分析精度的关键因素。以上述研究工作为基础，采用修正Suresh模型分别研究了拉伸变形与疲劳加载下HR3C /T92异种金属焊接接头典型局域（包括焊缝、熔合区和热影响区及母材等）的力学行为（包括残余应力、弹性模量、屈服强度、应变硬化指数等）及其分布特征。同时，应用数字图像相关技术同步测试了在拉伸与疲劳加载下上述焊接接头区的塑性变形非均匀分布。综合两种测试结果，重点研究了拉伸变形与疲劳加载下HR3C /T92异种金属焊接接头局域非均匀弹塑性变形场及其对接头局域力学性质（强度、刚度、塑性、韧性等）变化与残余应力动态演化的影响规律。本项目取得的成果将为进一步研究基于异种金属焊接接头局域力学行为动态劣化的疲劳损伤评定和抗疲劳设计方法提供坚实的实验基础，因此，具有重要的理论与工程实际意义。