The effect of the shape and size of initial flaws on crack propagation in uniaxially compressed linear brittle materials

Abstract

Explaining crack propagation in uniaxially compressed brittle solids is challenging because the complexity of such fracture makes it impossible to estimate the compressive capacity of a solid subjected to uniaxial compression using a well-defined, widely applicable formula. Localized tension is typically generated at the tip of a void in a solid under uniaxial compression, so we focus here on the geometrical possibilities of internal cavities and the impact of that geometry on crack propagation in a uniaxially compressed linear brittle solid. The study includes a review of the current understanding and limitations of knowledge of fracture in uniaxial compression and Finite Element based analyses of different initial void/cavity geometries and their impact on crack propagation. Analysis of crack propagation is carried out in terms of the mode I stress intensity factors associated with cracks propagating from different initial voids. Despite the analyses being limited to 2D, novel observations are discussed about the nature of crack propagation in uniaxial compression, confirming the complexity of this type of failure. The width (direct relationship), height (inverse relationship), size (direct relationship) and shape of the void are shown to be important in triggering crack propagation, but not the width-to-height ratio. An initial horizontal elliptical void with the major axis parallel to the applied compression and a minor axis 1/20 the length of the major axis was found to be the most critical void in terms of the likelihood to trigger cracks in uniaxial compression. Vertical elliptical voids were found to be less critical than all the other voids studied. The applicability of a stress intensity vs fracture toughness approach, as used to predict failure in tensile stress fields, is questioned.