【作者】 刘源；

【导师】 张桢；

【作者基本信息】 华中科技大学 ， 结构工程， 2022， 硕士

【摘要】 激光焊接作为一种新型的钢构件节点连接方式,在焊接强度、加工精度、热影响区大小方面与传统焊接技术(例如TIG,MIG和点焊)相比优势显著,在高端制造业领域已被广泛应用。激光焊接会在钢构件中留下自平衡的残余应力场,并在后续循环荷载作用下逐渐演化,其复杂的本构响应会影响焊接构件的疲劳性能。研究焊接残余应力松弛与非比例加载特性,对结构的整体安全性能评估及维护都具有重要意义。316L奥氏体不锈钢具有耐腐蚀性能强、高温强度好、良好的加工硬化性能、固溶状态无磁性等优点,在核电、土木工程等领域应用广泛。本文主要基于有限元方法并结合部分实验数据来对316L奥氏体不锈钢管激光焊接进行模拟,在此基础上对焊后残余应力场在比例与非比例加载下的响应进行研究。本文的工作内容主要由以下五部分组成,第一部分内容包括Lemaitre-Chaboche本构模型的公式推导及其在UMAT和Matlab中的算法实现,对316L奥氏体不锈钢在单多轴加载下的力学行为进行预测。第二部分内容包括利用黏弹塑性非比例硬化模型来探究加载路径及加载速率对316L奥氏体不锈钢力学性能的影响。第三部分内容包括在有限元软件ABAQUS中实现316L奥氏体不锈钢板焊接仿真,确定一套焊接模拟流程。第四部分内容包括利用ABAQUS UMAT模拟316L奥氏体钢管的激光焊接。第五部分内容包括利用UMAT实现焊接加载全流程模拟,对比例加载下的残余应力松弛情况进行预测,并对非比例加载和不同应变率加载下的残余应力演化情况进行探究。结果表明:1、单轴拉压循环加载和扭转剪切循环加载下焊接残余应力都有明显的松弛;2、不同的循环应变幅值对于焊接残余应力的松弛量有影响,表现为幅值越高松弛量越大;3、焊后残余应力演化与加载路径和加载速率有关,非比例硬化效应的引入会对非比例循环加载下焊后残余应力的演化产生影响,表现为残余应力随循环数增加逐渐攀升。更多还原

【Abstract】 Laser welding,as one of the most cutting edge joining techniques,offers users several benefits over traditional welding technology,for instance,TIG,MIG and spot-weldings,in weld strength,precision work,and limited heat affected zone.These advantages make laser welding highly competitve and been extensively applied in high-technology manufacturing industry.Nevetheless,laser welding is not very different from tranditional weldings in generating a self-equilibrated residual stress state in welded steel components.The residual stresses will evolve gradually under cyclic loading,together with the complex constitutive behavior,would substantially impact the fatigue performance of welded steel components.The study of residual stress relaxation and non-proportional loading is of great significance to the overall safety evaluation and maintenance of structures.Austenitic stainless steel 316L has been widely used in nuclear power plant and,civil engineering because of its excellent corrosion resistance,high temperature strength,and good work hardening properties.In this work,laser welded 316L austenitic stainless steel pipe was investigated based on numerical simulation and available experiments.The responses of residual stress field after welding under proportional and non-proportional loading were comprehensively analysed.This work was mainly composed of five parts.The first part introduced the derivation of constitutive relation of Lemaitre-Chaboche model and its numerical implementation.The constitutive behavior of 316L austenitic stainless steel was then studied under uniaxial and multiaxial loading.The second part investigated the effects of loading path and loading rate on mechanical response of 316L austenitic stainless steel,by using a visco-plastic non-proportional contitutive model.In the third part,a set of welding simulation procedure was established.The welding simulation of 316L austenitic stainless steel plate was carried out in the finite element software ABAQUS.The fourth part determined the heat source model based on available experimental data.The laser welding of 316L austenitic steel pipe is examined.The fifth part presented a welding and loading procedure based on UMAT.The relaxation of residual stress was investigated under cyclic loading.The proportional and non-proportional behavior of welded 316L stainless pipe was studied extensively by considering different loading paths and strain rates.The following results were reached:1.Welding residual stress was obviously relaxed under uniaxial tension-compression cyclic loading and torsional shear cyclic loading.2.Cyclic strain amplitude affected the relaxation of residual stress.The higher the strain amplitude,the greater the level of stress relaxation.3.The evolution of post-weld residual stress was related to loading path and loading rate.The evolution of post-weld axial residual stress would be differing under non-proprotional cyclic loading from proportional ones.The former shows that the magnitude of residual stresses increased gradually with the increasing number of cycles.更多还原