Study on mechanical characteristics and deterioration mechanism of frozen and melted coal under the action of liquid nitrogen
Liquid nitrogen can affect the mechanical properties of coal by changing the internal structure of coal seam.In order to study the mechanism of coal degradation under the action of liquid nitrogen,the frozen and melted coal samples are taken as the objects for research.The results show that the tensile and uniaxial compressive strength of coal body increases when frozen for more than 50 minutes at a time.With the increase of freezing time,the strength and elastic modulus show a trend of increasing and then decreasing;with the increase of freeze-thaw cycles,the coal body mechanics is reduced.The initial(0-10)cycles decline dramatically and the decline tends to be moderate.When the coal body damage caused by the freeze-thaw cycle is more serious,it is more likely for the thawed coal sample to form a dense fracture grid.In order to evaluate the freeze-thaw damage of coal in different states,the relative e-lastic modulus E is calculated,and the relationship between the number of freeze-thaw cycles and the rel-ative tensile strength σs and relative compressive strength σu is fitted.It decreases sharply in the early stage of freezing and thawing,and then tends to be gentle.
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