Uniaxial compression and tension tests of anthracite and loading rate dependence of peak strength

Okubo, Seisuke; Fukui, Katsunori; Qi, Qingxin

doi:10.1016/j.coal.2006.02.004

Cited by 104 publications

(45 citation statements)

References 7 publications

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“…Our results for larger specimens with lengths of 50 cm and 100 cm, however, showed that the simulated UCS decreases from the X to the Z to the Y direction. This decrease in strength with the axis of loading relative to bedding agrees with published laboratory testing results on coal (Okubo et al, 2006). to the Young's modulus and specimen size of the 10-cm specimens that are considered representative of the coal.…”

Section: Unconfined Compressive Strength Ucssupporting

confidence: 84%

“…This scale effect has been attributed to the various discontinuities observed within the coal, including cracks, bedding planes and butt and face cleats (Bieniawski, 1968b;St George, 1997). Discontinuities within coal result in an anisotropic fabric with varying strength and stiffness properties in relation to the orientation of the loading direction (Okubo et al, 2006;Pomeroy et al, 1971;Szwilski, 1984).…”

Section: Introductionmentioning

confidence: 97%

See 1 more Smart Citation

Numerical investigation of the scale effect and anisotropy in the strength and deformability of coal

Gao

Stead

Kang

2014

International Journal of Coal Geology

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Section: Unconfined Compressive Strength Ucssupporting

confidence: 84%

Section: Introductionmentioning

confidence: 97%

Numerical investigation of the scale effect and anisotropy in the strength and deformability of coal

Gao

Stead

Kang

2014

International Journal of Coal Geology

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“…Based on equation (3), n is not a constant and varies with strain rate. This finding conflicts with previous results [e.g., Okubo et al, 2006;Hashiba et al, 2006], which indicate that n is a constant and depends on material properties. This may be attributed to the wider range of strain rate we apply.…”

Section: Results Analysis and Discussioncontrasting

confidence: 99%

“…Apart from the microstructure itself, the strength and failure mechanisms of coal are also affected by the loading rate [ Okubo et al ., ]. Okubo et al .…”

Section: Introductionmentioning

confidence: 99%

Failure mechanisms in coal: Dependence on strain rate and microstructure

et al. 2014

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The brittle coal failure behavior under various axial strain rates from 10 À3 to 10 À2 s À1 is experimentally and numerically studied. The numerical microscale finite difference model is built on the accurate X-ray microcomputed tomography images, which provides a ground-breaking and bottom-up approach to investigate the effects of microstructure on coal failure under various strain rates. Experimentally, prior to loading, the coal sample is scanned, and the three-dimensional coal structure model is constructed. The microheterogeneous structures are incorporated in the model, which facilitates the deformation and failure mechanism analysis under different loading conditions. The results reveal that the microheterogeneous structures significantly affect the evolution of stress concentrations and deformation behaviors in the sample. The coal tends to fail in the shear mode before the peak strength, since the shear zone is created with high displacements. However, tensile failure ultimately controls the failure process after the peak strength. Notably, the strain rate dependence of coal strength is observed, and an empirical relationship is proposed to describe the dynamic strength of the coal under various loading strain rates. Importantly, the coal strengthens with an increase in strain rate. For brittle material, such as coal, the strength and failure mechanism are strain rate and microstructure dependent. The strain rate-dependent coal strength index (n) is found to be a dynamic parameter in the range of strain rate from 10 À3 to 10 À2 s À1, and this finding may extend the concept of strain rate dependence over a broader range of loading conditions.

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“…Okubo et al (1992), Ishizuka et al (1993), Ray et al (1999), Li and Xia (2000) and Kohmura and Inada (2006) conclude from their experimental results that rock uniaxial compressive strengths tend to increase with strain and loading rates, respectively. For brittle rocks the loading rate effects on the elastic modulus remain inconclusive (Blanton 1981;Chong et al 1987;Wang 2008;Okubo et al 2001Okubo et al , 2006. The mechanisms governing the loading-rate dependency for brittle rocks have been related to the time-dependent initiation and propagation of the micro-cracks and fractures in the rock matrix (Costin 1987;Zhang et al 1999;Li and Xia 2000;Aubertin et al 2000).…”

Section: Introductionmentioning

confidence: 96%

Influence of Loading Rate on Deformability and Compressive Strength of Three Thai Sandstones

Fuenkajorn

Kenkhunthod

2010

Geotech Geol Eng

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Uniaxial and triaxial compressive strength tests have been performed using a polyaxial load frame to assess the influence of loading rate on the strength and deformability of three Thai sandstones. The applied axial stresses are controlled at constant rates of 0.001, 0.01, 0.1, 1.0 and 10 MPa/s. The confining pressures are maintained constant at 0, 3, 7 and 12 MPa. The sandstone strengths and elastic moduli tend to increase exponentially with the loading rates. The effects seem to be independent of the confining pressures. An empirical loading rate dependent formulation of both deformability and shear strength is developed for the elastic and isotropic rocks. It is based on the assumption of constant distortional strain energy of the rock at failure under a given mean normal stress. The proposed multiaxial criterion well describes the sandstone strengths within the range of the loading rates used here. It seems reasonable that the derived loading rate dependent equations for deformability and shear strength are transferable to similar brittle isotropic intact rocks.

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Uniaxial compression and tension tests of anthracite and loading rate dependence of peak strength

Cited by 104 publications

References 7 publications

Numerical investigation of the scale effect and anisotropy in the strength and deformability of coal

Numerical investigation of the scale effect and anisotropy in the strength and deformability of coal

Failure mechanisms in coal: Dependence on strain rate and microstructure

Influence of Loading Rate on Deformability and Compressive Strength of Three Thai Sandstones

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