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Gold Science and Technology ›› 2019, Vol. 27 ›› Issue (1): 41-51.doi: 10.11872/j.issn.1005-2518.2019.01.041

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Study on Fracture Characteristics and Mechanical Properties of Brittle Rock Based on Crack Propagation Model

Xiang LI,Zhen HUAI,Xibing LI*(),Zhuoyao ZHANG   

  1. 1. School of Resources and Safety Engineering，Central South University，Changsha 410083，Hunan，China
  • Received:2018-01-08 Revised:2018-03-27 Online:2019-02-28 Published:2019-03-19
  • Contact: Xibing LI E-mail:xbli@mail.csu.edu.cn

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Abstract:

In order to study the influence of initial microcrack parameter distribution on fracture characteristics and mechanical properties of brittle rocks and further understand systematically the fracture evolution of brittle rocks， a two-dimensional mesoscopic elastic damage model of heterogeneity was established based on the theory of elastic fracture mechanics.The proposed model scheme was implemented through the two dimentional finite difference program FLAC2D.The zones in the model behave elastically before failure occurs, and lose tensile or shear load bearing capacity at corresponding mode of failure.Microcracks with different length and orientation distributions were defined in the zones of the model.The failure of the zone was controlled by the fracture propagation status of the microcrack inside.A failure criterion was adopted based on the stress intensity factor of the microcrack in each zone.The fracture process of rock specimens with different morphologies under distinct loading conditions was simulated using the proposed numerical model.The influence of the microcrack distributions on both the macroscopic fracture pattern and the mechanical response of the numerical model was analyzed.The results show that when the microcrack lengths and orientations are defined by different distributions，the different macroscopic fracture modes can be resulted.When the microcrack lengths and orientations are defined by normal distribution， failure band with clear shape can be formed.Failure zones are relatively dispersed if the microcrack lengths or orientations obey uniform or exponential distributions. For the reasons of shear failure and splitting failure of rock samples during the uniaxial compression test of brittle rock， the initial microcrack orientation was of guiding significance.When the mean initial microcrack orientation ɑ=45°， the minimum peak strength and axial maximum strain of model were obtained.The fracturing process of brittle rock uniaxial compression test， Brazilian splitting test and fracture toughness test were simulated.Good consistency was obtained with respect to both the mechanical response and fracture patterns.The model is valuable in rendering reliable results for rock mechanical tests which are difficult to realize in the laboratory. The inclusion of the influence of microcracks in simulating mechanical behavior of rock material also provide important insights into the failure process of rock under external load.

Key words: brittle rock, initial microcrack, crack propagation, failure mode, fracture toughness, numerical simulation

CLC Number: 

  • TU452

Fig.1

Probability density functions change diagram of Weibull distribution with different shape parameters β"

Fig.2

Heterogeneous model of cylindrical sample"

Fig.3

Initial microcrack propagation in the zone of the model"

Table 1

Basic parameters of numerical model"

参数数值参数数值
弹性模量E/GPa53.5形状参数β15
泊松比μ0.25摩擦系数0.3
体积模量K/GPa35.67Ⅰ型断裂韧度KⅠ/（MPa?m1/2）1.88
剪切模量G/GPa21.4Ⅱ型断裂韧度KⅡ/（MPa?m1/2）4.87

Fig.4

Effect of initial microcrack distribution on fracture characteristics of model under uniaxial compression state"

Fig.5

Effect of initial microcrack distribution on fracture characteristics of model under uniaxial tension state"

Fig.6

Macroscopic failure state of model with different initial mean orientations of microcracks under uniaxial compression state"

Fig.7

Stress-strain curves of rock models with different initial microcrack mean orientations under uniaxial compression state"

Fig.8

Schematic of uniaxial compression and fracture toughness test"

Table 2

Basic mechanical parameters of granite obtained from uniaxial compression test"

试样编号单轴抗压强度/MPa弹性模量E/GPa泊松比μ
均值137.0648.100.26
H1121.3440.350.20
H2154.0957.440.24
H3128.1049.270.26
H4136.8643.330.33
H5144.9350.110.25

"

断裂韧度类型编号P/kNr/mmR/mmB/mmNK/（MPa?m1/2）
Ⅰ型G1-011.648.525.225.61.1651.093
G2-010.428.524.526.10.987
G3-012.168.425.224.61.181
G4-011.108.725.425.21.063
G5-011.088.324.725.31.061
均值11.288.4825.025.361.077
Ⅱ型G1-26.710.868.425.325.21.8991.673
G2-26.710.688.524.425.71.682
G3-26.710.048.624.625.21.609
G4-26.710.228.525.426.21.517
G5-26.711.288.325.225.61.707
均值10.628.4624.9825.581.638

Table 4

Basic parameters of numerical model"

参数数值参数数值
弹性模量E48.1形状参数β15
泊松比μ0.26摩擦系数μ0.3
体积模量K/GPa33.4Ⅰ型断裂韧度KⅠ1.077
剪切模量G/GPa19.09Ⅱ型断裂韧度KⅡ1.638

Fig.9

Macroscopic rupture of model and sample under uniaxial compression state"

Fig.10

Stress-strain curves of model and sample under uniaxial compression state"

Fig.11

Macroscopic rupture of model and sample under tension state"

Fig.12

Load-displacement curves of model and sample under tension state"

Fig.13

Macroscopic rupture of model and sample in the fracture toughness test"

Fig.14

Peak load diagram of model and sample in the fracture toughness test"

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