A New Bursting Liability Evaluation Index for Coal –The Effective Elastic Strain Energy Release Rate

Zhiguo Lu, Wenjun Ju, Fuqiang Gao, Youliang Feng, Zhuoyue Sun, Hao Wang and Kang Yi
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Zhiguo Lu: Coal Mining and Designing Branch, China Coal Research Institute, Beijing 100013, China
Wenjun Ju: Coal Mining and Designing Branch, China Coal Research Institute, Beijing 100013, China
Fuqiang Gao: National Key Laboratory of Coal Mining and Clean Utilization, China Coal Research Institute, Beijing 100013, China
Youliang Feng: Coal Mining and Designing Branch, China Coal Research Institute, Beijing 100013, China
Zhuoyue Sun: Coal Mining and Designing Branch, China Coal Research Institute, Beijing 100013, China
Hao Wang: School of Energy Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, China
Kang Yi: Coal Mining and Designing Branch, China Coal Research Institute, Beijing 100013, China

Energies, 2019, vol. 12, issue 19, 1-15

Abstract: Because both faults and cleats exist in coal, sharp stress drops occur during loading when coal is deformed. These drops occur during the pre-peak stage and are accompanied by sudden energy releases. After a stress drop, the stress climbs slowly following a zigzag path and the energy accumulated during the pre-peak stage is unstable. A stress–strain curve is the basic tool used to evaluate the bursting liability of coal. Based on energy accumulation in an unsteady state, the pre-peak stress–strain curve is divided into three stages: pre-extreme, stress drop, and re-rising stage. The energy evolution of the specimen during each stage is analyzed. In this paper, an index called the effective elastic strain energy release rate (EESERR) index is proposed and used to evaluate the coal’s bursting liability. The paper shows that the propagation and coalescence of cracks is accompanied by energy release. The stress climb following a zigzag path prolongs the plastic deformation stage. This causes a significant difference between the work done by a hydraulic press during a laboratory uniaxial compression experiment and the elastic strain energy stored in the specimen during the experiment, so the evaluation result of the burst energy index would be too high. The determination of bursting liability is a comprehensive evaluation of the elastic strain energy accumulated in coal that is released when the specimen is damaged. The index proposed in this paper fully integrates the energy evolution of coal samples being damaged by loading, the amount of elastic strain energy released during the sample failure divided by the failure time is the energy release rate. The calculation method is simplified so that the uniaxial compressive strength and elastic modulus are included which makes the new index more universal and comprehensive. Theoretical analysis and physical compression experiments validate the reliability of the evaluation.

Keywords: bursting liability; unstable energy accumulation; effective elastic strain energy; stress drop (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2019
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