关于焊接残余应力形成机制的探讨

分析了关于焊接残余应力形成过程描述的传统观点的局限性和不足,指出材料力学的“截面法”不能用于分析横向残余应力分量。认为在不考虑材科相变的前提下,焊缝金属冷却时收缩受制也是导致焊接残余应力产生的重要原因。虽然残余压缩应变和残余收缩应变在导致焊接残余应力产生的作用方面是等价的,但其机理却有本质的不同,区别二者有利于研究和开发新的焊接残余应力调控技术。对固有应变理论进行了分析和补充,认为应统一到拉伸塑性应变上。用钢板上堆敷锡钎焊焊道的方法,在母材温升值低于塑性应变所需温差的条件下,由盲孔法测得了板上大范围分布的高值残余应力,且因焊道和母材的线膨胀系数差异较大,其应变测试值与环境温度有关。

Discussion and investigation on mechanism of welding residual stresses in mild steel

It is analyzed the limitation of traditional viewpoint which related the welding residual stresses only to the existence of plastic compressive deformation in weld and base metal.The authors believe that the method used in material mechanics called "section separating method" is not suitable for analysis of transverse residual stress in butt joint and the restrained contraction of weld during cooling plays a very important pole to residual stress forming procedure.Although the actions of the residual compressive strains and the residual contractive thermal strains are equivalent for causing the welding residual stress,it is useful distinguishing them to develop new measures relieving and adjusting the welding residual stress in practical joints.It is analyzed and modified to the application of inherent strain theory that should include mainly plastic tensile strains to welding residual stress.The very high residual stresses are measured by Mathar method from the experiment of depositing a soldering pass onto the mild steel plate under the condition of the temperature rising of the base metal lower than that needed for plastic compressive strains appearing,which verified the important role of restrained contracting of weld to the mechanism of welding residual stress.It is found that the strains measured have a close relation to the environment temperature for the great difference in linear expanding coefficient between the steel and the solder.