Experimental study of determining fracture toughness KIC of shale by semi-disk three-point bending

ZHAO Zi-jiang; LIU Da-an; CUI Zhen-dong; TANG Tie-wu; HAN Wei-ge

doi:10.16285/j.rsm.2018.0571

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Experimental study of determining fracture toughness KIC of shale by semi-disk three-point bending

更新时间：2026-06-25

- Experimental study of determining fracture toughness KIC of shale by semi-disk three-point bending
- Vol. 39, Issue S1, Pages: 258-266(2018)
- 作者机构：
  
  1. 中国科学院地质与地球物理研究所中国科学院页岩气与地质工程重点实验室,北京,100029
  2. 中国科学院地球科学研究院,北京,100029
  3. 中国科学院大学地球与行星科学学院,北京,100049
- 作者简介：
- 基金信息：
- DOI：10.16285/j.rsm.2018.0571
  CLC： TU452
- Online First：02 September 2018，
  
  Published：2018
- 稿件说明：
移动端阅览
ZHAO Zi-jiang, LIU Da-an, CUI Zhen-dong, et al. Experimental study of determining fracture toughness KIC of shale by semi-disk three-point bending[J]. 2018, 39(S1): 258-266.
DOI：

ZHAO Zi-jiang, LIU Da-an, CUI Zhen-dong, et al. Experimental study of determining fracture toughness KIC of shale by semi-disk three-point bending[J]. 2018, 39(S1): 258-266. DOI： 10.16285/j.rsm.2018.0571.

摘要

为了准确测试页岩的I型断裂韧度KIC，分别采用直切槽半圆盘试样（NSCB）和人字形切槽半圆盘试样（CCNSCB），在3种预制切槽布置模式（splitter、arrester、divider）下，开展三点弯曲加载实验。通过标准差和变异系数分析两类方法KIC测算值的离散性，并评价各自适用性。使用光学显微镜观察试件破裂后的裂纹扩展路径和破裂面断口形态。基于断裂力学理论，给出页岩试件粗糙起伏断口表面能计算公式，分析页岩试件实测值KIC离散的原因，并用最小耗能原理解释裂缝在页岩试件扩展过程中形成粗糙断裂面的机理。对比分析两种试样类型测试的KIC值，认为两种方法在切槽平行层理布置的情况下测算值离散程度一致，二者都适用；对于切槽垂直层理两种布置方式下NSCB试件更容易发生裂缝偏转，导致产生Ⅰ-Ⅱ复合型断裂，使试验失效；CCNSCB试件的韧带具有良好的裂缝扩展导向作用，某种程度上抵消了加载配置非对称性带来的不利影响，CCNSCB比NSCB测得的KIC值离散性更小，更适用于各向异性页岩的KIC测试。

Abstract

In order to accurately test the mode I fracture toughness(KIC) of shale

three point bending loading experiments are carried out using notched semi-circular bend(NSCB) and cracked chevron notched semi-circular bend(CCNSCB) samples under three types of prefabricated notches (splitter

arrester and divider)

respectively. According to statistical results of standard deviation and coefficient of variation

discreteness of each group of KIC values is analyzed; and applicability of the two methods is valued respectively. The crack propagation path and fracture surface morphology are observed by optical microscope. Based on fracture mechanics

we give the calculation formulas of the rough undulating fracture surface of shale specimens. The reason for KIC value scattering of the tested shale specimens is analyzed; and the formation mechanism of rough fracture surface in the expansion process is explained using the principle of minimum energy dissipation. By comparing the KIC values of the two sample types

CCNSCB and NSCB methods yield KIC values of similar discreteness when notches are parallel to bedding planes. When notches are vertical to layers

KIC values from CCNSCB specimens is more consistent than that from NSCB. The ligaments of CCNSCB specimens are in favor of crack propagation

which counteracts the adverse influence caused by asymmetry loading configuration to some extent. Therefore

CCNSCB specimens are more suitable to test fracture toughness of anisotropic shale than NSCB.

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