Effects of residual stress and heat treatment on fatigue strength of weldments

Effects of residual stress and heat treatment on fatigue strength of weldments were investigated with lateral link specimens and sway bar bracket specimens. Residual stresses in the thickness direction at a weld toe location were measured by the X-ray diffraction (XRD) method and the hole drilling method for as-welded and post-heat-treated specimens. Compressive residual stresses on the surface were obtained from the as-welded specimens, while zero or very low tensile residual stresses were obtained from the heat-treated specimens. Microstructural differences between as-welded and heat treated specimens were also investigated in this study. Heat-treated specimens showed fine grains at the weld zone compared to that of as-welded specimens. Fatigue strength of as-welded specimens was found higher than that of heat-treated specimens due to compressive residual stresses induced at the weld toe areas. This study also predicted the fatigue life of as-welded specimens with commercial fatigue software and the life predictions were compared with experimental results.