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Energies 2017, 10(4), 500;

Experimental Investigation on the Strength and Failure Behavior of Coal and Synthetic Materials under Plane-Strain Biaxial Compression

1,* , 3,†,* , 1
Key Laboratory of Deep Coal Resource Mining of Ministry of Education, School of Mines, China University of Mining & Technology, Xuzhou 221116, Jiangsu, China
Department of Energy and Mineral Engineering, EMS Energy Institute, and G3 Center, The Pennsylvania State University, University Park, PA 16802, USA
School of Resources & Safety Engineering, Central South University, Changsha 410083, Hunan, China
State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining & Technology, Xuzhou 221116, Jiangsu, China
All authors contributed equally to this work.
Authors to whom correspondence should be addressed.
Academic Editor: Mehrdad Massoudi
Received: 24 February 2017 / Revised: 31 March 2017 / Accepted: 1 April 2017 / Published: 7 April 2017
(This article belongs to the Section Energy Sources)
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An evaluation of the failures of coal under variable conditions in relation to the stability of coal pillars is an important issue for coal mining. This paper presents the results of an experimental investigation of the mechanical behavior of brittle coal under plane-strain biaxial stress state (PSBSS) compression. The synthetic specimens were meant to test the ductile properties. Modified surface instability detection apparatus was setup to carry out the tests. The results show that the stress-strain curves of coal and synthetic specimens under the PSBSS can be divided into four typical stages, namely original microcrack closure, elastic deformation, sudden stress drop, and residual behavior. The stress-strain curve of coal under PSBSS compression showed periodic stress drops during the post-peak phase, while the curve of the synthetic specimen presented a moderate decrease during the post-peak stage. The remarkable residual strengths of the coal and composites can be observed using these curves, which is vital to the stability of specimens after the failure strength is exceeded. Strain rates have a significant effect on the strength of coal samples under PSBSS compression. Specifically, a higher strain rate indicates a greater peak strength. The failure modes for coal and synthetic specimens are different. During PSBSS compressive tests, coal showed a split failure under different strain rates. For flexible composites, the failure pattern is conjugate shear failure. The study indicated that the Modified Lade and Modified Wiebols-Cook criteria are competent for estimating the defined strength coefficient, which is a ratio proposed to estimate the PSBSS peak strength. View Full-Text
Keywords: biaxial compression; coal; criterion; peak strength; plane-strain biaxial compression; coal; criterion; peak strength; plane-strain

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Zhang, H.; Wan, Z.; Ma, D.; Zhang, Y.; Cheng, J.; Zhang, Q. Experimental Investigation on the Strength and Failure Behavior of Coal and Synthetic Materials under Plane-Strain Biaxial Compression. Energies 2017, 10, 500.

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