A GENERALIZED CONCEPT OF A FATIGUE THRESHOLD

Abstract

Abstract— The conditions for non‐propagating LEFM type fatigue cracks were investigated on an Inconel, 617 Alloy in the range of K max between 10 and 50 MPa m 1/2 under four different types of fatigue loading conditions. In all tests, K max was held constant during the fatigue cycling prior to determining the non‐propagation condition. It was found that with decreasing range of applied K the fatigue tolerance range Δ K eff, th increases. Furthermore, there is slight increase of Δ K eff,th with decreasing K max of approximately 20–30% when K max is decreased from 50 to 10 MPa m 1/2 . The results of the four types of tests are considered in respect to the damage in the near‐region of the crack front, i.e. increasing K max increases the damage zone and therefore decreases the fatigue tolerance range Δ K eff,th .