Abstract
To accurately determine the true strain-rate effect of granite in split Hopkinson pressure bar (SHPB) tests, systematic experimental studies from quasi-static to dynamic loading on the same batch of granite samples is required. Therefore, firstly, splitting, uniaxial and triaxial compression tests were used to study the mechanical response of granite under different static stress conditions with the MTS rock mechanics test system, and the impact compression tests were performed at different strain-rates by the split Hopkinson pressure bar (SHPB). The test results show that the compressive strength increases with the increase of confinement, but the increase rate decreases as the confinement gets larger. The axial failure strain also increases with the increase of confinement. Failure is related to the composition and structure of granite, as well as the stress state. With increasing confinement, the sample is more constrained, the elastic limit strain becomes smaller, and the elastic modulus becomes larger accordingly. In addition, shear slip failure takes place under triaxial compression. In the dynamic compression tests, the strain-rate affects not only the strength of granite, but also the degree of fragmentation and the breaking pattern. Also, it has been found that the dynamic compressive strength enhancement of rocks under impact loading is due to the combined effects of the material strain-rate, lateral inertia and end friction; however, in SHPB tests they are coupled together and could not be separated from each other. To determine the material strain-rate effect of rocks in the SHPB tests, the dynamic compressive strength enhancement caused by the lateral inertial effect and end friction effect needs to be removed. Assuming that the effect of the material strain-rate, lateral inertia and end friction is uncoupled, the numerical simulation method has been employed to simulate the SHPB tests on granite. The true strain-rate effect of granite in SHPB tests is thus determined.
Highlights
The strength and deformation characteristics of rocks are the foundation of rock engineering design and theoretical analysis
Together with other researchers’ studies (Brace and Jones, 1971; Bischoff and Perry, 1991; Li and Meng, 2003; Zhou and Hao, 2008; Liang et al, 2008; Li et al, 2009; Lu et al, 2010; Mu et al, 2012; Hao et al, 2012), it is shown that the lateral inertial effect and the end friction effect are the key factors to cause the increase of dynamic increase factor (DIF) in addition to the strain-rate effect of rock material itself, and the three factors are mutually coupled
A numerical simulation method is required to determine the lateral inertia effect and end friction effect of granite samples, and the dynamic compressive strength enhancement caused by the lateral inertial effect and end friction effect, respectively, is eliminated from the measured dynamic compressive strength of granite samples
Summary
The strength and deformation characteristics of rocks are the foundation of rock engineering design and theoretical analysis. Together with other researchers’ studies (Brace and Jones, 1971; Bischoff and Perry, 1991; Li and Meng, 2003; Zhou and Hao, 2008; Liang et al, 2008; Li et al, 2009; Lu et al, 2010; Mu et al, 2012; Hao et al, 2012), it is shown that the lateral inertial effect and the end friction effect are the key factors to cause the increase of DIF in addition to the strain-rate effect of rock material itself (here called the true strain-rate effect), and the three factors are mutually coupled. Dynamic compression tests are conducted with φ 75 mm SHPB device
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