FATIGUE LIFE ESTIMATION FOR HFMI TREATED WELDMENTS CONSIDERING WELD TOE MAGNIFICATION FACTOR

摘要

HFMI (High-Frequency Mechanical Impact) post-treatment is a statistically proven method to significantly improve fatigue life of welded structures. Positive effects of improved fatigue life by the HFMI treatment are attributed to the weld toe geometry and the compressive residual stress. This study investigates the effect of geometric and mechanical effects by HFMI treatment on fatigue life with an explicit consideration of the weld magnification factor M_k. The conventional fatigue life estimation method to assess the effect of HFMI treatment by an experiment and analysis involves significant expense and time. In this regard, this study suggests an improved method by using M_k weld magnification factor and the stress ratio to assess the effect of HFMI post-treatment in more efficient manner. First step of this method is to calculate M_k weld magnification factor in HFMI treated condition to consider the geometrical effect by HFMI treatment at weld toe region. Second, the stress ratio model is introduced to consider the compressive residual stress by HFMI treatment based on Paris equation. The result is obtained by Paris-Erdogan equation for a S355 material. The result from this study is validated by a comparison with a previous fatigue test of HFMI treated welded specimen.