Study on the Fatigue Crack Propagation Rate

Fatigue Crack Propagation Behaviour in the Hardnes Heterogeneous Field (Part 1)

Abstract

Fatigue crack propagation rate in weld metal or H.A.Z. does not always increase monotonously under conditions of constant alternating and maximum stress. In this report, the effect of the hard region on the fatigue crack propagation rate was investigated.
Fatigue tests were performed on specimens containing the hard region under load controlled four point bending and edge crack tension.
When a fatigue crack was remote from the soft-hard boundary, its propagation rate was increased monotonously. The crack comming near the boundary, the hard region was found to reduce the increrrlent of its propagation rate restricting the plastic zone. Fatigue crack propagation rate had a relationship with the cyclic crack opening displacement. The distance from the soft-hard boundary to the point where the increment of propagation rate was beginning to be reduced was related to the cyclic crack opening displacement at that point.