Similarities in the fracture surface features of borosilicate and polymer glasses

Abstract

Considerable similarity exists between the features on the fracture surfaces of a borosilicate glass and those on the fracture surfaces of polymer thermoset glasses like epoxies and vinyl esters. These features include the steps and welts of the hackle, the arrays of skewed cracks, and the basic longitudinal texture. It was the latter, the basic longitudinal texture, that was the most surprising find on the fracture surfaces of borosilicate glass. On the fracture surfaces of polymer thermoset glasses, the basic longitudinal texture has been interpreted as a remnant from the fracturing process, arising from an instability in the meniscus between air and a polymer layer softened or “liquified” by the stresses of cracking. The meniscus instability results in an array of crack fingers preceding the nominal crack front. By analogy, it is suggested that the borosilicate glass fractures by a similar process, including the softening of the glass ahead of the crack front. The basic longitudinal texture is usually visible only at high magnification and often requires (a necessity for the borosilicate glass fracture surface) the tilting of the normal to the fracture surface toward the detector. The steps, welts and arrays of skewed cracks are simply explained with the crack fingering hypothesis.