1 Introduction

Since linear elastic fracture mechanics (LEFM) was derived from the work of Griffith (1921), it has been assumed that the stored elastic strain energy that is involved in extending a crack in a brittle material becomes potential surface energy associated with the new surface as it is created. Thus the area of new surface that can be created in a fracture episode should be limited by the amount elastic strain energy input before the fragmentation episode. We conducted laboratory and field (rock avalanche) measurements to test this assumption and consistently found more fracture surface area than the assumption would predict. Nevertheless, this result does not affect conventional LEFM because it is unaffected by the fate of the elastic strain energy in brittle failure. We see evidence that the elastic strain energy that causes cracks to propagate in individual grains becomes transient elastic strain, and influences further breakage. This result has broad and growing significance as developing technologies allow ever finer fragments to be detected and measured in brittle fracture.

2 Borosilicate glas fragmentation

Kolzenberg et al. (2013) report dry confined compression tests on borosilicate glass (Pyrex), presenting the elastic strain energy released at failure and total surface area of the fragmented samples. We have carried out unconfined compression tests on dry 10mm diameter and 20 mm long borosilicate glass (Pyrex) cylinders; four tests yielded fragments with estimated total surface area up to 91.8 m2. Since the specific surface energy of borosilicate glass is established as 4.5 Jm−2 (Wiederhorn 1969), this would require about 413 J, but the elastic strain energy available at failure was about 133 J.

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