An analysis of complex electromagnetic radiation signals induced by fracture

As shown at the Laboratory of Rock Mechanics, electromagnetic radiation (EMR) emitted by propagating fractures provides relatively accurate information on the dimensions of the cracks emitting it. In this paper we demonstrate that this method (i.e. EMR analysis) can also be advantageously used for obtaining the exact time sequence of double or triple pulses when they appear simultaneously and, hence, the sequence of the relevant cracks. The method is first used to analyse the time sequence of a triple fracture during failure and for a double fracture in relaxation of a glass ceramic sample. The analysis is in good agreement with the actual fractography of the sample. A similar procedure applied to fracture of chalk enabled us to show that most large fractures are, in fact, double, and to find the specific time sequences involved.