Quantification of CTOD fracture toughness in welded joints to evaluate the efficacy of vibration stress relief compared to thermal stress relief

Resonant vibration residual stress relief (R-VSR) is an alternative method to post-weld heat treatments (PWHT) which is said to lead to less distortion and lower costs. The method of superposition of cyclic stresses and residual stresses, which can lead to localized yielding of the material, dislocation movement and subsequent stress relief. This article aims at investigating the efficiency of resonant vibration in the relief of residual stresses in welded joints of HSLA Domex700 steel sheets. Mechanical stress relief was compared to a common PWHT, and stress levels were then quantified through X-ray diffraction. Samples were also characterized by CTOD fracture toughness tests, fractographic analysis and tensile tests. Results indicate that the mechanical method was significantly less effective in relieving stresses in comparison with the PWHT, but led to apparent improvements in fracture toughness and in tensile tests. FWHM values indicated significant distortion for PWHT and less distortion for R-VSR.

共振振动消应力法（Resonant vibration residual stress relief, R-VSR）是焊后热处理（post-weld heat treatments, PWHT）的替代工艺，据称可有效降低焊接变形与生产成本。该方法通过循环应力与残余应力的叠加作用，使材料产生局部屈服、位错运动，进而实现残余应力的消减。本文旨在探究共振振动法对高强度低合金（High Strength Low Alloy, HSLA）Domex700钢板焊接接头的残余应力消减效能。研究中将机械消应力法与常规焊后热处理进行对比，并通过X射线衍射（X-ray diffraction）量化应力水平。此外，还采用裂纹尖端张开位移（Crack Tip Opening Displacement, CTOD）断裂韧性试验、断口形貌分析与拉伸试验对试样进行表征。结果表明，相较于焊后热处理，机械消应力法的应力消减效果显著更弱，但在断裂韧性与拉伸性能方面均呈现出明显提升。半高宽（Full Width at Half Maximum, FWHM）数值显示，焊后热处理会引发显著变形，而共振振动消应力法的变形程度更低。