Fatigue Crack Growth Behaviour and Role of Roughness-Induced Crack Closure in CP Ti: Stress Amplitude Dependence

Abstract

This paper investigated the fatigue crack propagation mechanism of CP Ti at various stress amplitudes (175, 200, 227 MPa). One single crack at 175 MPa and three main cracks via sub-crack coalescence at 227 MPa were found to be responsible for fatigue failure. Crack deflection and crack branching that cause roughness-induced crack closure (RICC) appeared at all studied stress amplitudes; hence, RICC at various stages of crack propagation (100, 300 and 500 µm) could be quantitatively calculated. Noticeably, a lower RICC at higher stress amplitudes (227 MPa) for fatigue cracks longer than 100 µm was found than for those at 175 MPa. This caused the variation in crack growth rates in the studied conditions.

Fracture Mechanics and Fatigue Design in Metallic Materials

“…The closure of the crack was discussed in three articles [5][6][7]. Zakavi et al [5] presents new tools to evaluate the crack front shape of through-the-thickness cracks propagating in plates under quasi-steady-state conditions.…”

“…Ahmed et al [7] investigated the fatigue crack propagation mechanism of CP Ti at various stress amplitudes. One crack at 175 MPa and three main cracks via sub-crack coalescence at 227 MPa were found to be responsible for the fatigue failure.…”