The Life Assessment by Linear Cumulative Damage Rule for Cold Dwell Fatigue of Ti-6Al-4V

Abstract

Fatigue life of Ti alloys is decreased by tensile stress dwell even at room temperature, which is called Cold Dwell Fatigue (CDF). CDF is similar to creep-fatigue of some metals (stainless steel, Ni-base alloy, and so on) in the point of decrease of fatigue life with stress or strain dwell at high temperature. In this study, time exhaustion rule and ductility exhaustion rule based on linear cumulative damage rule were calculated for CDF life assessments. In the case of time exhaustion rule, total damage was calculated as D_F+D_C< (0.03, 0.015) (D_F: fatigue damage, D_C: creep damage). In the case of ductility exhaustion rule, total damage was calculated as D_F+D_C~1. Additionally, the feature of fracture surfaces after CDF tests changed with increase of dwell time. This trend corresponded to the balance between fatigue damage and creep damage calculated by ductility exhaustion rule.