Research of fracturing mechanism of coal subjected to liquid nitrogen cooling

Abstract

In order to research fracturing mechanism of coal subjected to liquid nitrogen cooling, submersion tests of liquid nitrogen for natural coal samples are carried out. A laser microscope is employed to observe the extension of native crack and propagation of cracks of coal samples after thermal shock. Then the fracture mechanics theory is used to analyze the extension mechanism of the crack during thermal shock. The main conclusions include: 1) Liquid nitrogen cooling causes temperature tensile stress and the stress concentration. When the stress intensity factor is more than the fracture toughness of coal native crack, the native crack will extend. 2) The temperature tensile stress makes the particle clusters with low tensile strength around the native crack fail and break off, and the destruction of the structure of the coal sample causes microcrack initiation. 3) There is a great effect of cooling time on the stress intensity factor. With the increasing of the temperature gradient and the cooling time, the stress intensity factor increases, with more susceptibility for coal to rupture.

Keywords

• coal geology
• liquid nitrogen cooling
• native fissures
• stress intensity factor
• crack extension