Abstract

For understanding acoustic emission (AE) activity and accumulation of micro-damage inside rock under pure tensile state, the AE signals has been monitored on the test of directly tension on two kinds of marble specimens. A tensile constitutive model was proposed with the damage factor calculated by AE energy rate. The tensile strength of marble was discrete obviously and was sensitive to the inside microdefects and grain composition. With increasing of loading, the tensile stress–strain curve obviously showed nonlinear with the tensile tangent modulus decreasing. In repeated loading cycle, the tensile elastic modulus was less than that in the previous loading cycle because of the generation of micro damage during the prior loading. It means the linear weakening occurring in the specimens. The AE activity was corresponding with occurrence of nonlinear deformation. In the initial loading stage which only elastic deformation happened on the specimens, there were few AE events occurred; while when the nonlinear deformation happened with increasing of loading, lots of AE events were generated. The quantity and energy of AE events were proportionally related to the variation of tensile tangent modulus. The Kaiser effect of AE activity could be clearly observed in tensile cycle loading. Based on the theory of damage mechanics, the damage factor was defined by AE energy rate and the tensile damage constitutive model was proposed which only needed two property constants. The theoretical stress–strain curve was well fitted with the curve plotted with tested datum and the two property constants were easily gotten by the laboratory testing.

Highlights

  • IntroductionAcoustic emission (AE) or microseismic (MS) technology have become an important mean to study rock failure process and determine stability of rock mass because of its capability in real-time monitoring of signal released by rock in external damage

  • Acoustic emission (AE) or microseismic (MS) technology have become an important mean to study rock failure process and determine stability of rock mass because of its capability in real-time monitoring of signal released by rock in external damage (Liu et al 2017; Prikryl et al.2003; Xiao et al 2016; Wang et al 2017; Cao et al 2016; Hall et al 2006; He et al 2014; Li and Li 2017)

  • Compared to the numbers of acoustic emission (AE) events occur in compressive tests (Hou 2017), there are obviously less in direct tensile test and almost no AE events were detected at the initial loading stage

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Summary

Introduction

Acoustic emission (AE) or microseismic (MS) technology have become an important mean to study rock failure process and determine stability of rock mass because of its capability in real-time monitoring of signal released by rock in external damage The results showed that AE activities of rock specimens under direct tensile was different from that of splitting and uniaxial compression. It is considered that initiation and expansion of fracture under the condition of tensile stress are the main mechanism to control specimen destruction, which leads to later appearance of AE signal. In the aspect of direct tensile damage model of rock, Jin and Qian (1998) proposed nonlinear elasticity constitutive equation by analyzing increasing law of inelastic deformation under tensile stress. Direct tensile test was conducted on two kinds of marble with monitoring the AE activity, and tensile damage constitutive model was established based on AE parameters to explore failure mechanism of direct tensile status on marble

Experiment method
Mechanical parameter of the specimens
AE activity for specimens under direct tensile process
AE activity in tensile cyclic loading test
Tensile constitutive equation based on AE energy
Tensile damage factor
Damage constitutive model in tensile state for rock material
Findings
Conclusions
Full Text
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