煤样三点弯曲裂纹扩展及断裂力学参数研究

doi:10.13722/j.cnki.jrme.2020.0736

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Abstract Fracture of quasi-brittle materials such as coal involves a distributed microcracking region around the crack tip，called fracture process zone(FPZ). This non-linear FPZ influences both the strength and the stability of a coal structure，and often makes the linear elastic fracture mechanics(LEFM) fail to describe the fracture process of coal samples. To better understand the non-linear phenomena of coal fractures，three-point bending tests of coal beams with a center notch were performed. The integrated acoustic emission(AE) and digital image correlation(DIC) techniques were used to track the crack propagation during pre-peak and post-peak stages visually. Based on the equivalent linear elastic fracture mechanics(ELEFM)，the fracture parameters were calculated，and the fracture criterion and the crack propagation speed were also analyzed and discussed. Additionally，comparison between theory and test results was performed. The results indicate that，at the pre-peak regime，the FPZ of coal is gradually developing with a fully developed FPZ length of 7.5 mm and a critical opening displacement of 38.4 μm from three separate tests of the same material. During the crack propagation in the post-peak regime，the FPZ length and the critical opening displacement keep constant，while the traction-free crack length increases with CMOD，leading the increment of the effective crack length. Most of the AE events are located within or surrounding the FPZ，which indicates that the AE are mainly from the microcracking activities in the FPZ. Using ELEFM，the average calculated fracture toughness KIC is 0.316 MPa·，and the critical energy release rate Gc by Irwin¢s relation is in the range of 39.6–40.4 N/m which is very close to the fracture energy Gf = 36.2–39.6 N/m determined following a RILEM recommendation. The post-peak response during crack propagation follows the fracture criterion of KI = KIC if FPZ is considered，from which the theory CMOD-load curve agrees well with the experiment result. Both theory and experimental results show that the crack speed decreases as the crack length increases.

Key words： mining engineering three-pending bending acoustic emission(AE) digital image correlation(DIC) equivalent linear elastic fracture mechanics(ELEFM) fracture process zone(FPZ) fracture parameters

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	WANG Xiaoran1
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	WANG Enyuan1
	2
	LIU Xiaofei1
	2
	LI Nan3
	ZHOU Xin1
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Cite this article:

WANG Xiaoran1,2,WANG Enyuan1, et al. Three-point-bending test of crack propagation and fracture parameters of coal specimens[J]. , 2021, 40(4): 690-702.

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https://rockmech.whrsm.ac.cn/EN/10.13722/j.cnki.jrme.2020.0736 OR https://rockmech.whrsm.ac.cn/EN/Y2021/V40/I4/690

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