Effect of Grinding on Flaw Geometry and Fracture of Glass

Abstract

Fracture mechanics is combined with fracture surface analysis to analyze brittle failure of glass bars which were tested relative to the direction of grinding. Grinding essentially produces two sets of flaws from which failure occurs. In the most severe set, formed basically parallel to the grinding direction, the ratio of the average depth (a) to the half‐width (b) is 0.5. In the less severe set, formed perpendicular to the grinding direction, the average a/b ratio is 1.6. In both sets the most severe flaws are generally associated with a particularly deep grinding groove or gouge. The strength reduction resulting from testing perpendicular to the grinding direction results from the larger flaw size and slightly higher stress‐intensity factor resulting from the greater ellipticity of the flaws formed parallel to the grinding grooves and perpendicular to the tensile axis. Detailed analysis of these 2 sets of flaws causing failure of appropriately oriented specimens shows that (1) the fracture mirror radius, r, occurs at a constant stress‐intensity level independent of flaw geometry; (2) unsymmetric fracture mirrors result from unsymmetric, irregular flaws leading to unsymmetric stress‐intensity distributions; (3) is constant for semielliptical flaws; and (4) fracture energy calculated from an expression including mirror constants, the flaw‐to‐mirror size ratio, and the flaw geometry agrees with measured values over a wide range of a/b values.

Analysis of subcritical crack growth in dental ceramics using fracture mechanics and fractography

“…The rate of SCG is a power law function of stress intensity factor [9]. The shapes of the flaws within the material affect the stress intensity factor such that sharp flaws and flaws with high depthto-width ratios correspond to greater stress intensity factor at the same stress level and hence faster SCG than blunt flaws and flaws with low depth-to-width ratios [13]. Additionally, the presence of moisture usually has a deleterious effect [14].…”

Fracture analysis of an all-ceramic bearing system

“…al. 16 showed that grinding introduces two types of microcracks: one which is parallel to the grinding direction and one which is perpendicular to the grinding direction. The parallel microcracks are typically more severe.…”

Experimental study on glass edge machining flaw characterization

“…Other sources discuss the existence of machining-induced flaws that have been studied using fractographic observations [26,22]. Similarly the failure origins were associated with machining damage [27] and grinding-induced cracks [28,29].…”

“…Machining strongly influences the configuration of the entire edge flaw population, and thus the final strength of a bended specimen [22].…”