Acoustic emission of quasi-isotropic rock samples initiated by temperature gradients

The influence of temperature gradients and heating rate on crack formation in quasi-isotropic samples of marble and sandstone is studied using acoustic emission records. The behavior of velocities and attenuation of elastic waves in the samples is also examined. The crystallographic textures of marble and sandstone are measured by the neutron diffraction method, and it is shown that temperature gradients of up to 52°C/cm do not lead to a change in the textures. It is established that the temperature dependence of acoustic activity in the sandstone samples strongly depends on the internal heating rate. The maximum acoustic activity of the sandstone samples was observed at maximum temperature gradients in the samples. The temperature dependence of acoustic activity in marble differs significantly from that in sandstone. Maximums of acoustic activity in the marble samples are observed at temperatures of 30–60 and higher than 200°C. A decrease in acoustic activity was recorded in the interval between these temperatures. Such behavior suggests a predominant role of the surface structure and the concentration of surface defects in the process of crack formation in marble. During cooling, all samples demonstrate similar behavior: maximum acoustic activity is observed at the switching-off of the heating element and the emission activities of different samples are comparable in intensity.