温度冲击下煤的微观结构变化与断裂机制
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摘要
为研究温度冲击下煤的微观结构变化及其损伤断裂机制,以干燥颗粒煤为研究对象,分别开展了煤样的冷冲击和热冷冲击试验。利用扫描电镜(SEM)观测图像结果,分析对比了两种温度冲击前后煤样微观形貌、裂缝分布、开裂和延伸情况,结合断裂力学理论分析了煤样内部微裂缝的开裂机制和扩展方向,并通过ANSYS有限元软件模拟了微裂缝扩展时的应力场和位移场的分布情况,揭示了煤样的断裂机制。研究结果表明,两种温度冲击对煤的结构均造成了不同程度的破坏,温度冲击所形成的热应力最终导致了原始裂纹和新生裂纹的扩展和延伸;温度冲击下所产生的裂纹形式主要有沿晶裂纹、穿晶裂纹、翼型裂纹、交叉裂纹、枝须状裂纹和网状裂纹;分析结果表明,温差愈大,所产生的温度热应力愈大,热冷冲击所产生的裂缝的数量更多、扩展更充分,对煤样的破坏更严重,因此,热冷冲击的破煤效果更好。
To study the microstructure change of coal and its damage and fracturing mechanism under temperature shock, cold impact and hot-cold impact tests were carried out on dry granular coal. The micro-morphology, fracture distribution, cracking and extension of coal samples before and after temperature impact were analyzed and compared by scanning electron microscopy(SEM). The cracking mechanism and propagation direction of micro-cracks in coal samples were analyzed based on fracture mechanics theory. The distributions of stress and displacement fields during micro-crack propagation were simulated by ANSYS finite element software to reveal the fracturing mechanism of coal samples. The results showed that the structure of coal was destroyed by two types of temperature shocks, and the thermal stress induced by temperature shocks eventually led to the expansion and extension of the original crack and the new crack. The main types of cracks induced by temperature impact were intergranular crack, transgranular crack, airfoil crack, cross crack, dendritic whisker crack and mesh crack. It is revealed that a bigger temperature difference results in a higher thermal stress. Hot-cold impact can generate more cracks and more extensive crack propagation than cold impact, leading to more serious damage of coal samples. Therefore, the hot-cold impact has better coal breaking effect than the cold impact.
To study the microstructure change of coal and its damage and fracturing mechanism under temperature shock, cold impact and hot-cold impact tests were carried out on dry granular coal. The micro-morphology, fracture distribution, cracking and extension of coal samples before and after temperature impact were analyzed and compared by scanning electron microscopy(SEM). The cracking mechanism and propagation direction of micro-cracks in coal samples were analyzed based on fracture mechanics theory. The distributions of stress and displacement fields during micro-crack propagation were simulated by ANSYS finite element software to reveal the fracturing mechanism of coal samples. The results showed that the structure of coal was destroyed by two types of temperature shocks, and the thermal stress induced by temperature shocks eventually led to the expansion and extension of the original crack and the new crack. The main types of cracks induced by temperature impact were intergranular crack, transgranular crack, airfoil crack, cross crack, dendritic whisker crack and mesh crack. It is revealed that a bigger temperature difference results in a higher thermal stress. Hot-cold impact can generate more cracks and more extensive crack propagation than cold impact, leading to more serious damage of coal samples. Therefore, the hot-cold impact has better coal breaking effect than the cold impact.
引文
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[22]ASHBY M F,HALLAM S D.The failure of brittle solids containing small cracks under compressive stress states[J].Acta Metallurgica,1986,34(3):497-510.
[23]SANDERSON T J O.Ice mechanics:Risks to offshore structures[M].[S.l.]:Graham&Trotman,1988.
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[25]郭少华,孙宗颀,谢晓晴.压缩条件下岩石断裂模式与断裂判据的研究[J].岩土工程学报,2002,24(3):304-308.GUO Shao-hua,SUN Zong-xin,XIE Xiao-qing.Research on mode and criterion of rock fracture under compressive loading[J].Chinese Journal of Geotechnical Engineering,2002,24(3):304-308.
[26]李相麟.混凝土斜裂纹损伤断裂分析[J].南昌大学学报(工科版),2004,26(4):56-58.LI Xiang-lin.Damage and fracture analysis on concrete with an oblique crack[J].Journal of Nanchang University(Engineering&Technology),2004,26(4):56-58.
[27]李灏.断裂力学[M].济南:山东科学技术出版社,1980.LI Hao.Fracture mechanics[M].Jinan:Shandong Science and Technology Press,1980.
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(18A620001)and the Science Research Funds of Henan Polytechnic University(J2018-1).
[2]叶建平,史保生,张春才.中国煤储层渗透性及其主要影响因素[J].煤炭学报,1999,24(2):118-122.YE Jian-ping,SHI Bao-sheng,ZHANG Chun-cai.Coal reservoir permeability and its controlled factors in China[J].Journal of China Coal Society,1999,24(2):118-122.
[3]MCDANIEL B W,GRUNDMANN S,KENDRICK W,et al.Field applications of cryogenic nitrogen as a hydraulic fracturing fluid[J].Journal of Petroleum Technology,1997,50(3):38-39.
[4]杨兆中,张云鹏,贾敏,等.低温对煤岩渗透性影响试验研究[J].岩土力学,2017,38(2):354-360.YANG Zhao-zhong,ZHANG Yun-peng,JIA Min,et al.Experimental research on influence of low temperature on coal permeability[J].Rock and Soil Mechanics,2017,38(2):354-360.
[5]张春会,张海霞,于永江,等.饱水度和再溶浸对液氮冷冻煤致裂的影响[J].煤炭学报,2016,41(增刊2):400-406.ZHANG Chun-hui,ZHANG Hai-xia,YU Yong-jiang,et al.Effects of saturation and re-submersion on coal fracturing subjected to liquid nitrogen shock[J].Journal of China Coal Society,2016,41(Supp.2):400-406.
[6]吴世跃,郭勇义.注气开采煤层气增产机制的研究[J].煤炭学报,2001,26(2):199-203.WU Shi-yue,GUO Yong-yi.Study of the mechanism of increasing production of exploitation coal-bed methane by gas injection[J].Journal of China Coal Society,2001,26(2):199-203.
[7]杨新乐,任常在,张永利,等.低渗透煤层气注热开采热-流-固耦合数学模型及数值模拟[J].煤炭学报,2013,38(6):1044-1049.YANG Xin-le,REN Chang-zai,ZHANG Yong-li,et al.Numerical simulation of the coupled thermal-fluid-solid mathematical models during extracting methane in low-permeability coal bed by heat injection[J].Journal of China Coal Society,2013,38(6):1044-1049.
[8]QIN L,ZHAI C,LIU S,et al.Changes in the petrophysical properties of coal subjected to liquid nitrogen freeze-thaw-A nuclear magnetic resonance investigation[J].Fuel,2017,194:102-114.
[9]ZHAI C,QIN L,LIU S,et al.Pore structure in coal:Pore evolution after cryogenic freezing with cyclic liquid nitrogen injection and its implication on coalbed methane extraction[J].Energy Fuel,2016,30(7):6009-6020.
[10]COETZEE S,NEOMAGUS H W J P,BUNT J R,et al.The transient swelling behaviour of large(-20+16 mm)South African coal particles during low-temperature devolatilisation[J].Fuel,2014,136(10):79-88.
[11]TRAN D,SETTARI A,NGHIEM L.Initiation and propagation of secondary cracks in thermo-poroelastic media[C]//46th US Rock Mechanics/Geomechanics Symposium.Chicago:American Rock Mechanics Association,2012.
[12]CAI C,LI G,HUANG Z,et al.Experiment of coal damage due to super-cooling with liquid nitrogen[J].Journal of Natural Gas Science&Engineering,2015,22:42-48.
[13]魏建平,孙刘涛,王登科,等.温度冲击作用下煤的渗透率变化规律与增透机制[J].煤炭学报,2017,42(8):1919-1925.WEI Jian-ping,SUN Liu-tao,WANG Deng-ke,et al.Change law of permeability of coal under temperature impact and the mechanism of increasing permeability[J].Journal of China Coal Society,2017,42(8):1919-1925.
[14]MCDANIEL B W,GRUNDMANN S,KENDRICK W,et al.Field applications of cryogenic nitrogen as a hydraulic fracturing fluid[J].Journal of Petroleum Technology,1997,50(3):38-39.
[15]任韶然,范志坤,张亮,等.液氮对煤岩的冷冲击作用机制及试验研究[J].岩石力学与工程学报,2013,32(增刊2):3790-3794.REN Shao-ran,FAN Zhi-kun,ZHANG Liang,et al.Mechanisms and experimental study of thermal-shock effect on coal-rock using liquid nitrogen[J].Chinese Journal of Rock Mechanics and Engineering,2013,32(Supp.2):3790-3794.
[16]李和万,王来贵,张春会,等.液氮对含水煤样裂隙疲劳增扩作用的试验研究[J].实验力学,2016,31(1):119-126.LI He-wan,WANG Lai-gui,ZHANG Chun-hui,et al.Experimental study of the fatigue crack extension influence of liquid nitrogen on water cut coal sample[J].Journal of Experimental Mechanics,2016,31(1):119-126.
[17]王登科.含瓦斯煤岩本构模型与失稳规律研究[D].重庆:重庆大学,2009.WANG Deng-ke.Research on constitutive models and instability rules of gas-saturated coal[D].Chongqing:Chongqing University,2009.
[18]王登科,尹光志,刘建,等.三轴压缩下含瓦斯煤岩弹塑性损伤耦合本构模型[J].岩土工程学报,2010,32(1):55-60.WANG Deng-ke,YIN Guang-zhi,LIU Jian,et al.Elastoplastic damage coupled model for gas-saturated coal under triaxial compression[J].Chinese Journal of Geotechnical Engineering,2010,32(1):55-60.
[19]王登科,刘淑敏,魏建平,等.冲击破坏条件下煤的强度型统计损伤本构模型与分析[J].煤炭学报,2016,41(12):3024-3031.WANG Deng-ke,LIU Shu-min,WEI Jian-ping,et al.Analysis and strength statistical damage constitutive model of coal under impacting failure[J].Journal of China Coal Society,2016,41(12):3024-3031.
[20]杨起.中国煤田地质学[M].北京:煤炭工业出版社,1979.YANG Qi.Coal geology in China[M].Beijing:Coal Industry Press,1979.
[21]谢和平.岩石材料的局部损伤拉破坏[J].岩石力学与工程学报,1988,7(2):147-154.XIE He-ping.The local extension failure of damaged rock materials[J].Chinese Journal of Rock Mechanics and Engineering,1988,7(2):147-154.
[22]ASHBY M F,HALLAM S D.The failure of brittle solids containing small cracks under compressive stress states[J].Acta Metallurgica,1986,34(3):497-510.
[23]SANDERSON T J O.Ice mechanics:Risks to offshore structures[M].[S.l.]:Graham&Trotman,1988.
[24]杨卫.宏微观断裂力学[M].北京:国防工业出版社,1995.YANG Wei.Macro and micro fracture mechanics[M].Beijing:National Defense Industry Press,1995.
[25]郭少华,孙宗颀,谢晓晴.压缩条件下岩石断裂模式与断裂判据的研究[J].岩土工程学报,2002,24(3):304-308.GUO Shao-hua,SUN Zong-xin,XIE Xiao-qing.Research on mode and criterion of rock fracture under compressive loading[J].Chinese Journal of Geotechnical Engineering,2002,24(3):304-308.
[26]李相麟.混凝土斜裂纹损伤断裂分析[J].南昌大学学报(工科版),2004,26(4):56-58.LI Xiang-lin.Damage and fracture analysis on concrete with an oblique crack[J].Journal of Nanchang University(Engineering&Technology),2004,26(4):56-58.
[27]李灏.断裂力学[M].济南:山东科学技术出版社,1980.LI Hao.Fracture mechanics[M].Jinan:Shandong Science and Technology Press,1980.
[28]刘晓洲.冻土断裂破坏准则及其试验研究[M].北京:科学出版社,2015.LIU Xiao-zhou.Failure criterion of permafrost fracture and its experimental study[M].Beijing:Science Press,2015.
[29]康健.岩石热破裂的研究及应用[M].大连:大连理工大学出版社,2008.KANG Jian.Research and application of thermal fracture of rock[M].Dalian:Dalian University of Technology Press,2008.
(18A620001)and the Science Research Funds of Henan Polytechnic University(J2018-1).