Experimental Study on Mesodamage of Migmatite Under Cyclic Loading and Unloading

Abstract

To study the mesodamage of migmatite under cyclic loading, single cycle loading and unloading tests of migmatite were carried out under different confining pressures (σ3) and stress ratios (p), and acoustic emission (AE) technology was used to monitor the evolution of microcracks. Additionally, the mesodamage of migmatite was analyzed from the porosity and T2 spectrum distribution measured by nuclear magnetic resonance (NMR) spectroscopy. The results show that the peak stress ratios (pmax) of migmatite under different σ3 are different, and as the value of σ3 increases, the migmatite gradually undergoes a change from tension to shear failure. Moreover, with the increase in σ3, high-frequency signals gradually appeared, indicating that the increase of σ3 to a certain extent limited the generation of large size microcracks. The variations in damage variables defined by the number of AE hits and porosity are the same, “steep increment type,” and increase suddenly when approaching pmax. Furthermore, σ3 slightly affects the pore throat distribution of migmatite. In addition, σ3 has a certain inhibitory effect on the porosity of migmatite and accumulation of mesodamage. However, when σ3 exceeds a critical value, the inhibitory effect becomes a promoting effect.