The effect of specimen shape and strain rate on uniaxial compressive behavior of rock material

Abstract

The mechanical properties of rock material with length/diameter ratios varying from 1.0 to 3.0 were determined using a newly developed servo-hydraulic machine at a wide range of strain rates. The uniaxial compressive strength, initiation and dilatancy stresses, peak axial strain, and strain energy gradually decreased with increasing length/diameter ratios at the same loading condition; for the same length/diameter ratio, these properties increased with increasing strain rate. The elastic modulus increased with increasing specimen shape and strain rate, whereas the Poisson's ratio was independent on these two factors. The fracture modes were significantly dependent on both strain rate and specimen shape. When the strain rate was below 10 -3 s -1 , splitting was the main fracture mode for the short specimens while the shearing fracture mode dominates the longer specimens; when the strain rate was above 10 -3 s -1 , the fracture mode changed directly from cone-shaped fractures to shearing fractures. The recommended length/diameter ratio was 2.5 at strain rates of 10 -5 -10 -2 s -1 .

An Experimental Study on Determination of Crack Propagation Energy of Rock Materials under Dynamic (Impact) and Static Loading Conditions

“…The energy level under the static load and deflection graphs which was found to be lower than energy levels obtained with the Charpy impact test for all rock materials tested in this study confirms that energy consumption for crack propagation increases with an increase in loading rate [16][17][18][19]. The crack propagation time increasing with a decrease in the loading rate is accepted to be a reason for the issue of measuring energy level under static load to be lower than those obtained from the impact test [20][21][22].…”

A Modified Bursting Energy Index for Evaluating Coal Burst Proneness and Its Application in Ordos Coalfield, China

“…This system has two controlling modes during test and can record data simultaneously. According to Liang et al [39], the uniaxial compressive strength increases as loading rate increases and the recommended loading strain rate is from 10 −5 to 10 −3 s −1 . Therefore, in this study, displacement control mode with a constant speed of 0.002 mm/s was selected.…”

Mechanical Behavior and Energy Evolution of Sandstone considering Slenderness Ratio Effect

“…As a rule, the length-to-diameter ratio (D � length/diameter) for a cylindrical specimen or the height-to-width ratio for a plane strain specimen is regarded as slenderness ratio [22], and the analytical methods for shape effect can be divided into three categories: statistical theories based on Weibull theories, empirical and semiempirical models, and theories based on fracture mechanics [23]. Much of the research has been based on specimens of nonstandard dimensions and shapes and over a limited size range as summarized by Liang et al [24]. Masooumi et al [12] proposed a multiaxial failure criterion for intact rock incorporating shape effect and found some parameters in the criterion are shape-dependent.…”