Creep characteristics of coal and rock investigated by nanoindentation

Sun, Changlun; Li, Guichen; Gomah, Mohamed Elgharib; Xu, Jiahui; Sun, Yuantian

doi:10.1016/j.ijmst.2020.08.001

Cited by 42 publications

(12 citation statements)

References 46 publications

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“…According to the characteristics of some creep curves, the model established needs to reflect the mechanical characteristics of the elastic strain phase, deceleration creep phase, steady creep phase and accelerated creep phase [26,27]. Most scholars describe the creep process utilizing the Nishihara model (Figure 1), where I is a Hooker body, II is a Kelvin body, and III is a viscoplastic body.…”

Section: Rock Creep Modelmentioning

confidence: 99%

Experimental Study of Creep Acoustic Emission Characteristics of Coal Bodies around Boreholes under Different Moisture Contents

et al. 2021

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Water content is an important factor in the deformation-destruction process of coal bodies. To analyze the influence of water on the creep acoustic emission (AE) characteristics of coal rock surrounding a borehole, we conducted graded loading creep AE tests of single-hole specimens with different water contents (0%, 4%, 8% and water-saturation) under uniaxial loading. The findings include the following: the water content affects the creep mechanical properties of the coal body around a borehole. The creep transient strain and steady-state strain increased exponentially with rising water content; the saturated specimen showed the highest increase, reaching 44.5% and 28.6%, respectively. The specimen water content affected the cumulative ringing count (CRC) and the axial strain during creep. The axial strain increased with rising water content, the CRC increased linearly with rising axial strain. The higher the water content, the greater the CRC rise. At different stress levels, the CRC in the 4%, 8% and saturated water content specimens changed by 43%, 53% and 74%, respectively. The AE ringing rate showed a pattern of grow–decline–stabilize at each creep stage. The AEs decreased significantly with the rising water content and the creep curve lagged behind the AE data. This paper provides guidelines for gas extraction, borehole maintenance and AE detection.

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Section: Rock Creep Modelmentioning

confidence: 99%

Experimental Study of Creep Acoustic Emission Characteristics of Coal Bodies around Boreholes under Different Moisture Contents

et al. 2021

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“…However, this method has disadvantages, as it requires a large sample size while being time-consuming and expensive [7][8][9][10]. Comparatively, nanoindentation only requires a small shale sample, and has been developed as a reliable technique to characterize the microscale creep behavior of shales [8,[11][12][13][14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

Modeling the Viscoelastic Behavior of Quartz and Clay Minerals in Shale by Nanoindentation Creep Tests

et al. 2022

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The viscoelastic behavior of minerals in shales is important in predicting the macroscale creep behavior of heterogeneous bulk shale. In this study, in situ indentation measurements of two major constitutive minerals (i.e., quartz and clay) in Longmaxi Formation shale from the Sichuan Basin, South China, were conducted using a nanoindentation technique and high-resolution optical microscope. Firstly, quartz and clay minerals were identified under an optical microscope based on their morphology, surface features, reflection characteristics, particle shapes, and indentation responses. Three viscoelastic models (i.e., three-element Voigt, Burger’s, and two-dashpot Kelvin models) were then used to fit the creep data for both minerals. Finally, the effects of peak load on the viscoelastic behavior of quartz and clay minerals were investigated. Our results show that the sizes of the residual imprints on clay minerals were larger than that of quartz for a specific peak load. Moreover, the initial creep rates and depths in clay minerals were higher than those in quartz. However, the creep rates of quartz and clay minerals displayed similar trends, which were independent of peak load. In addition, all three viscoelastic models produced good fits to the experimental data. However, due to the poor fit in the initial holding stage of the three-element Voigt model and instability of the two-dashpot Kelvin model, Burger’s model is best in obtaining the regression parameters. The regression results indicate that the viscoelastic parameters obtained by these models are associated with peak load, and that a relatively small peak load is more reliable for the determination of viscoelastic parameters. Furthermore, the regression values for the viscoelastic parameters of clay minerals were lower than those of quartz and the bulk shale, suggesting the former facilitates the viscoelastic deformation of shale. Our study provides a better understanding of the nanoscale viscoelastic properties of shale, which can be used to predict the time-dependent deformation of shale.

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“…Recently, the holding states of nanoindentation experiments have been widely used to analyze the time-dependent deformations of biomaterials [10], metals and alloys [11,12], ceramics [13,14], polymers and composites [15][16][17][18], types of cement [19,20], and even crystals [21,22]. Besides, the estimation of the macrofracture toughness of minerals and rocks is given in [23], while the analysis of the micromechanical properties of mineral crystal grains is becoming more and more extensive [24][25][26]. All those above mean that the experimental technique was a robust way to conduct creep tests.…”

Section: Introductionmentioning

confidence: 99%

“…e quasi-static mechanical analysis (QMA) method and the dynamic mechanical analysis (DMA) method that was regarded as two basic approaches to conduct nanoindentation creep tests [29] were respectively used in above the two articles. And for other geomaterials obtained in coal mines, such as coal, mudstone, and sandstone, the quasi-static mechanical analysis method was also widely used to reveal their timedependent deformation phenomenon [25,30].…”

Section: Introductionmentioning

confidence: 99%

Explanation on the Abnormal Behavior during the Nanoindentation Holding Stages by Amplifying Oscillation

et al. 2022

Advances in Civil Engineering

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Recently, the holding states of nanoindentation experiments have been widely used to analyze the time-dependent deformations of various rocks, and the dynamic mechanical analysis (DMA) method seems to be more applicable than the quasi-static mechanical analysis (QMA) method when the influence of creep deformation on mechanical properties of rocks was analyzed. However, the former method causes an abnormal behavior during the creep holding stages that was not clearly interpreted.2 Consequently, in this study, by amplifying the oscillation of the DMA method, the mechanical mechanism of this phenomenon was explained. Experimental results confirm that the rheological deformation of rocks consists of the creep deformation (depth increasing) and the elastic aftereffect deformation (depth decreasing) during the creep time with small oscillation; once the elastic aftereffect deformation exceeds the creep deformation, the abnormal behavior can be observed. Besides, some other abnormal behaviors might be found for other rock materials when the DMA method with different oscillations is used, which illustrates the complexity and limitation of applying this method. Thus, the QMA method was recommended to investigate the above questions in future studies.

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Creep characteristics of coal and rock investigated by nanoindentation

Cited by 42 publications

References 46 publications

Experimental Study of Creep Acoustic Emission Characteristics of Coal Bodies around Boreholes under Different Moisture Contents

Experimental Study of Creep Acoustic Emission Characteristics of Coal Bodies around Boreholes under Different Moisture Contents

Modeling the Viscoelastic Behavior of Quartz and Clay Minerals in Shale by Nanoindentation Creep Tests

Explanation on the Abnormal Behavior during the Nanoindentation Holding Stages by Amplifying Oscillation

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