Stress intensity-dependent relation between overload plastic zone and fatigue retardation in Al-alloy

Abstract

Unveiling tensile overload (OL) influence during constant amplitude fatigue is fundamental to life prediction of random fatigue load. Although the same OL results in the same plastic-zone size for a material, subsequent fatigue retardation strongly depends on applied stress intensity, e.g. stress ratio R. This study attempts to separate the contributions of OL-induced residual stress (RS) related to crack closure and applied stress, crack-tip damage zone (DZ), and R-ratio depended crack deflection. To this end, fatigue tests are comparatively analyzed based on combination of different R ratios, the same OL condition, and removing DZ and crack-tip plastic zone. The results show that the fatigue retardation induced by the same OL decreases with increasing R, and the delay retardation disappears after removing DZ at R = 0.7 case. In addition, the OL-induced crack deflection is more obvious at low R = 0.1–0.4 cases than that at R = 0.7 case.