Effect of direct heating on cracking process in the uniaxially compressed sample

A suggestion was made in a number of published papers that the effect of electromagnetic exposure on the seismic regime in natural conditions or on the crack formation process in laboratory experiments can be explained by the role of Joule heating when electric current passes through fluid-saturated rocks. Heating of the fluid in the pore space can lead to an increase in the fluid pressure in the pores and cracks, which in turn can stimulate additional cracking of the solid skeleton and a decrease in the strength of the rock. In this paper, in order to identify the role of the thermal factor on the crack formation process in rocks, the results of direct heating of artificial sandstone samples under uniaxial compression are presented. The samples were taken from the same batch that was previously studied in experiments on the effect of electric current passing through a sample on the characteristics of acoustic emission and on the process of its destruction. In the presented experiments, the heat flux was supplied to the opposite side faces of the sample using Peltier elements, which are a reverse thermoelectric converter. The heat flux density on the sample surface reached almost 104 W/m2; the local temperature of the outer surface of the sample near the heating element increased during the heating process by 10-15°C depending on the duration of the current being turned on. Experiments have shown that even with such significant heat fluxes, the effect of heating is manifested only at loads close to destructive (Kp ≥ 0.95-0.97). The effect of heating was manifested in the fact that the crack formation process in the sample intensified, and the sample itself gradually passed into a overcritical state and, eventually, was destroyed. At lower loads, direct heating of the sample does not have a noticeable effect on the crack formation process.

trigger effect, rock destruction, thermal effect, acoustic emission, crack formation process