低温液氮冷冻煤体脆性-延性转化研究

Research on conversion of brittleness to ductility of coal with liquid nitrogen cryogenic

为了探究液氮冷冻对煤体断裂特性的影响及原因,对无烟煤和焦煤煤样进行液氮冷冻处理,通过单轴压缩试验,对比了液氮冷冻与未冷冻煤样的应力-应变曲线;通过超声波试验与核磁共振试验,对比了液氮冷冻前后煤体裂隙体积的变化,探讨了粘结力、摩擦力的变化对煤体断裂力学性质的影响。研究结果表明,与未冷冻煤样相比,液氮冷冻处理后的无烟煤和焦煤由脆性转化为延性,脆性指标分别降低了75.9%和63.5%,并且发现了液氮低温处理导致煤体裂隙体积的增加,是煤体脆性-延性转化的直接原因。分析得出了液氮冷冻煤体粘结力减小与摩擦力的增加,是煤体由脆性转化为延性的本质原因。

In order to study the reasons of rupture characteristics of coal under the influence of liquid nitrogen cryogenic(LN2),the thesis disposed the anthracite and coking coal cylinder with LN2,based on uniaxial compression testing,the stress-strain curve of cryogenic and non-cryogenic coal samples were acquired.According to results of low field NMR and ultrasonic tests,the volume of fractures were compared.The variation of adhesive property and friction have an influence on fracture mechanics were discussed.The results show that compared with the non-cryogenic coal samples,the brittleness index decreased 75.9% and 63.5% respectively.The increment of fracture volume was discovered to be the immediate cause of brittleness-ductility change.The fracture mechanical changes of adhesive property and friction were discussed and the essential reason of brittleness changes to ductility is that adhesive property decrease and friction increase of coal after LN2 cryogenic.