Study on mechanical response and strain of frozen coal after ultra-low temperature

In order to systematically analyze the mechanical response and strain evolution of frozen coal samples after liquid nitrogen (LN2) freezing, based on MTS testing machine to carry out uniaxial compression test. The stress–strain curves of coal samples under different time of LN2 freezing were obtained. The influence mechanism of LN2 freezing on mechanical properties of coal is analyzed. The results show that: (1) With the increase of freezing time and moisture content, the deformation of coal sample decreases under the action of ice cementation, and the closing strain and peak strain decrease. (2) Uniaxial compressive strength, elastic modulus and quality indexes of coal samples decrease with the increase of freezing time and moisture content. (3) The elastic energy of uniaxial loaded coal samples is positively correlated with freezing time and moisture content. (4) Using scanning electron microscopy analysis. After freezing by LN2, fractures in coal samples expand and connect, which result in mechanical properties deterioration. The higher the moisture content and the longer the freezing time, the stronger the deterioration effect of mechanical properties after freezing.