Analysis of the proximity-effect of a before mark on the behind one on the fracture surface of a brittle plastic sheet.

Abstract

A fracture surface mark is known to be formed by an interference between a primary crack front and a secondary crack front. We have shown so far that many such marks have been observed on a fracture surface of a brittle plastic specimen. The primary crack front passing through a before mark produces the succeeding behind mark as it propagates in the material, and the effect of the before mark often appears in the behind one. The cusp of the latter usually extends further as the two mark5 are closer together in front and in the rear on a fracture surface. For example, the experimentally measured chordal length at the nucleus of the behind mark increases as they close. Here, we define the proximity p* to express the linear distance between the nuclei of the two marks in front and in the rear, and we modify the previously reported equation of fracture surface marks to express those changes as a function of the proximity of the two. This expression, of course, gives better parabola-like configuration of the observed behind mark than the previous one.