Rock and Soil Mechanics ›› 2021, Vol. 42 ›› Issue (4): 1115-1125.doi: 10.16285/j.rsm.2020.6336

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Effect of different notch prefabrication methods and notch lengths on rock three-point bending test

LU Hao1, 2, FENG Xia-ting1, 3, YANG Cheng-xiang3, ZHANG Xi-wei3   

  1. 1. State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan, Hubei 430071, China 2. University of Chinese Academy of Sciences, Beijing 100049, China 3. Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines, Northeastern University, Shenyang, Liaoning 110819, China
  • Online:2021-04-12 Published:2021-08-25
  • Contact: ZHANG Xi-wei, male, born in 1976, PhD, Professor, research interest: rock mechanics experiments.
  • About author: LU Hao, male, born in 1996, Master candidate, research interest: rock three-point bending experiment.
  • Supported by:
    the National Key Research and Development Program of China (2018YFC0407006)

Abstract:  To select an appropriate notch prefabrication method and notch length for obtaining relatively accurate and reliable rock mode I fracture toughness (KIC), as well as to improve understanding of macro fracture process and meso-fracture characteristics in the rock three-point bending test, three methods, i.e., wire cutting, saw blade cutting and water jet cutting were used to prefabricate notch in granite and marble specimens for three-point bending test. The comparison of micro fracture characteristics among three different cutting methods was conducted with the application of scanning electronic microscopic. The test results show that the effect of wire cutting method on KIC is the smallest. In addition, three-point bending tests on granite and marble containing dimensionless notch length of 0.1, 0.2, 0.3, 0.4, and 0.5 show that KIC tends to increase firstly and then decrease with increasing notch length. The dimensionless notch length of α = 0.3 is recommended for obtaining the representative KIC. The macroscopic failure of rock specimen undergoes a process of initiation of localization zone, development of localization zone, crack initiation, and finally fracture propagation. The acoustic emission process of rock specimen is observed with an obvious brittle characteristic, the crack opening displacement curve is consistent with the trend of cumulative acoustic emission curve, and the evolution of crack opening displacement curve can be regarded as a macroscopic characterization of the specimen internal failure development process. 

Key words: rock three-point bending test, mode I fracture toughness, notch prefabrication method, notch length, fracture process