Absorbed Versus Released Energy in the Cracking Process of Heterogeneous Materials Under Compression

Abstract

In this investigation, the energy absorbed or released in the post-peak regime of heterogeneous materials subjected to compression are evaluated and distinguished. To this aim, uniaxial compression tests have been carried out on different types of rocks, such as limestone, marble and granite. The obtained overall responses, in terms of load versus displacement curves, are very different and variable from ductile to brittle, with the appearance of catastrophic snap-back instabilities, even for the same size and slenderness. In the case of snap-back instabilities, in order to obtain the complete load–displacement response, the tests have been controlled by the circumferential strain with a linked chain placed around the cylindrical specimen at mid-height. The absorbed energy per unit surface is computed through the overlapping constitutive law. Such a parameter, that results to be almost constant by varying the size-scale of the specimen, is compared to the elastic energy accumulated in the body at the point of instability to define a structural brittleness index. Finally, the released energy is put into relation to the different kinds of energy emissions detected during the loading process, namely, mechanical, electromagnetic, and nuclear.