Welding induced residual stresses are an important factor to consider when evaluating fatigue design of welded automotive parts. Fortunately, design engineers have various residual stress mitigation technologies at their disposal for improving the fatigue performance of these parts. For this purpose, it is essential to understand the relationship between the residual stresses and fatigue performance quantitatively as well as qualitatively.
It has been widely accepted that tensile residual stresses in welded structures are as high as the material yield strength level. Therefore, the fatigue strength of welded joints is governed predominantly by the applied stress range, regardless of the load ratio. However, in stress relieved components the tensile residual stress level is not as high, and the weld fatigue behavior is more influenced by the load ratio.
In this study, the fatigue behaviors of weldments, which shows different levels of residual stress distributions in the weld regime, were investigated using the existing fatigue data for various materials. The characteristics of the weld fatigue behaviors for three levels of residual stresses were investigated. From the investigation, Battelle structural stress based effective load ratio parameter incorporating residual stress effect, which is a function of crack growth, was proposed. In order to perform the fatigue cycle calculation, Battelle’s crack growth model was re-integrated using the effective load ratio parameter.
The validation of the proposed fatigue life evaluation procedure was conducted using various fatigue test data including residual stress distributions. The proposed procedure demonstrated reasonable predicted fatigue lives compared with test results. Therefore, this proposed procedure can be used to improve fatigue design of the welded components which contain complex residual stress distributions.