Using high speed video imaging in the study of cracking processes in rock

Abstract

This paper presents the use of a high speed video system (high speed camera) in studying the crack initiation, propagation, and coalescence in rocks. Prismatic laboratory-molded gypsum and Carrara marble specimens, which contained either a single artificial flaw or a pair of artificial flaws, were tested in uniaxial compression. The front face of the specimen was monitored by a high speed camera. By adopting an appropriate frame rate (1000 to 24 000 frames/s) and image resolution (256 by 512 to 1024 by 1024 pixels) of the high speed camera, we were able to observe the abrupt and violent cracking processes in rocks. In particular, it was possible to distinguish shear and tensile crack mechanisms, which so far was not possible and subject to many discussions in rock mechanics. Distinguishing the cracking details allowed us to record and interpret the entire cracking sequence. The aims of this paper are twofold. First, it briefly addresses the capability of the high speed camera technology to set the stage. Second, and this is the major contribution, it presents two comprehensive examples of how the interpretation of high speed videos is carried out to retrieve useful information on the cracking processes in rocks. Copyright © 2009 by ASTM International.