Unstable crack growth in a component subject to constant applied loads. II: Effect of crack size and component width

Abstract

When a crack grows slowly, by, for example, a stress corrosion mechanism, in a component that is subject to constant applied loads, it is possible that there will be a transition from slow growth to unstable non-environmentally-assisted (plastic) growth. Part I of this investigation 1 examined the plane strain deformation of a non-work-hardening solid containing two symmetrically situated deep cracks, and with tension of the small remaining ligament. The main conclusion was that the transition from stress corrosion crack growth to plastic crack growth, accompanied by instability, should not occur under constant load conditions until the general yield state is almost attained, even though a material's resistance to plastic crack growth might be only moderate. The present paper extends the earlier study by analysing the more general model of a solid of finite width containing two symmetrically situated cracks of equal depth. Irrespective of the crack size and solid width, it is shown that unstable plastic crack growth should not occur until the general yield state is almost attained, even if the plastic crack growth resistance is only moderate. The scope of the conclusion reached in Part I is therefore broadened, and the results therefore provide further support for the view that the occurrence of unstable plastic fracture under load control conditions approximately correlates with the attainment of a critical net-section stress across the remaining ligament. The results consequently provide additional underpinning for the currently used empirical net-section stress approach for predicting failure under load control conditions.