Effect of Crack Blunting on Subsequent Crack Propagation

TL;DR

This paper investigates how crack blunting affects subsequent crack propagation and dislocation emission, using an extended lattice Greens function approach to model the process and quantify the increased load needed for crack growth.

Contribution

It introduces a Cavity Greens Function method to model crack blunting effects, extending previous lattice Greens function techniques.

Findings

Crack blunting slightly increases the load required for propagation.

Blunting influences dislocation emission and crack stability.

Relevance to brittle and ductile materials with dislocation activity.

Abstract

Theories of toughness of materials depend on an understanding of the characteristic instabilities of the crack tip, and their possible interactions. In this paper we examine the effect of dislocation emission on subsequent cleavage of a crack and on further dislocation emission. The work is an extension of the previously published Lattice Greens Function methodology. We have developed a Cavity Greens Function describing a blunt crack and used it to study the effect of crack blunting under a range of different force laws. As the crack is blunted, we find a small but noticeable increase in the crack loading needed to propagate the crack. This effect may be of importance in materials where a dislocation source near the crack tip in a brittle material causes the crack to absorb anti-shielding dislocations, and thus cause a blunting of the crack. It is obviously also relevant to cracks in more ductile materials where the crack itself may emit dislocations.