Fracture mechanics analysis of a surface crack in an HFMI-treated joint based on numerical influence factor method

Kurzfassung

To elucidate the mechanism of fatigue strength improvement by High-Frequency Mechanical Impact (HFMI), it is necessary to analyze fatigue crack propagation considering the change of the toe profile and compressive residual stresses (RS) distribution caused by HFMI treatment. In previous studies (e.g., Leitner, M. et al., Weld. World (2014) 58,1:29-39), the RS distribution in the HFMI groove was approximated by a simple uniaxial stress distribution, and only the Mode I stress intensity factor (SIF) was evaluated. In this study, the mixed-mode SIF (MM-SIF) of surface cracks HFMI-treated T-welded joints is calculated with high accuracy using an automatic mixed-mode influence coefficient (IC) database generation system for surface cracks in welded joints developed by Kyaw et al. (Theor. Appl. Fract. Mech. (2020) 106:102471). The RS distribution is calculated by welding thermal elastic-plastic finite element (FE) analyses and peening dynamic explicit elastic-plastic FE analyses. It is found that the SIF becomes positive in the absence of RS, but becomes negative when HFMI’s RS is taken into account. Abrupt circumferential changes in mode II/III SIF for the crack in an HFMI joint. This change is considered to be caused by the disturbance of the surface profile and RS distribution at the beginning and end of the HFMI process.