Heterogeneous materials in compression: Correlations between absorbed, released and acoustic emission energies

Compression tests on concrete and rocks - limestone, marble and granite - specimens have been carried out to investigate on the correlation between absorbed, released and acoustic emission energies. To this aim, the complete load vs. displacement curves have been obtained up to complete failure, evidencing very different post-peak responses - variable from normal softening to catastrophic snap-back - by varying the material, even for the same size and slenderness. Due to the expected brittle behaviour of some of the considered specimens, the loading process has been controlled by means of the circumferential strain with a linked chain placed around the cylindrical specimen at mid-height. The absorbed energy per unit surface is then computed through the overlapping constitutive law. Such a parameter, that results to be almost scale-invariant, is compared to the elastic energy accumulated in the body at the point of instability to define a structural brittleness index. Furthermore, all the tests have been monitored by means of the acoustic emission technique. The obtained data have been analysed in details, in order to draw a connection with the released energy in the post-peak regime, and to discriminate the different failure mechanisms.