Discrete element simulation of dynamic semi-circular bend flexure tests of rocks using split Hopkinson pressure bar
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ORIGINAL PAPER
Discrete element simulation of dynamic semi-circular bend flexure tests of rocks using split Hopkinson pressure bar Yuan Xu 1 & Feng Dai 1 & Nu-wen Xu 1 & Tao Zhao 1 & Cheng Zhou 1
Received: 21 February 2016 / Accepted: 20 June 2016 # Saudi Society for Geosciences 2016
Abstract The semi-circular bending (SCB) using a split Hopkinson pressure bar system appears to be a promising method for measuring dynamic flexural strength of rock materials due to its distinct advantages. The quasi-static analysis is adopted for determining the dynamic flexural strength, of which several vital prerequisites have not been thoroughly examined yet. In this study, dynamic flexure tests regarding dynamic force equilibrium, interfacial friction effects, and energy partitioning are numerically investigated based on discrete element method (DEM) modeling. Results show that by virtue of the ramped wave loading, the force equilibrium of the specimen can be effectively achieved and the rupture is precisely measured to synchronize with the peak force, both of which guarantee the quasi-static data reduction method employed to determine the dynamic flexural strength; while the opposite occurs for the test under a rectangular wave loading. Furthermore, dynamic flexural strengths obtained by the numerical SCB tests exhibit approximately linear rate dependence that is identical with the experimental results. The interfacial friction, which is found to significantly influence the measuring results for rather high loading rates, contributes to enhancing the rate dependence of flexural strength and must be taken into account in dynamic flexure tests. In addition, energy partitioning is first numerically performed in the dynamic SCB tests and the nominal fracture energy manifests an S type of rate dependence with loading rates.
* Feng Dai [email protected]
1
State Key Laboratory of Hydraulics and Mountain River Engineering, College of Water Resources and Hydropower, Sichuan University, Chengdu, Sichuan 610065, China
Keywords SHPB . Dynamic flexure . Discrete element method . Friction effects . Energy partitioning
Abbreviations BPM Bonded particle model DEM Discrete element method ISRM International Society for Rock Mechanics SCB Semi-circular bending SHPB Split Hopkinson pressure bar As Area of the fracture surface (m2) B Thickness of the SCB sample (m) FIc Force on the incident end of the specimen (N) FTc Force on the transmitted end of the specimen (N) Gdc Fracture energy dissipated per unit area (J/m2) Uf Accumulated energy consumed to fracture during the failure process of SCB (J) P1 Axial force applied on the incident end of the sample (N) P2 Axial force applied on the transmitted end of the sample (N) R Radius of the SCB sample (m) S Span of the supporting pins (m) ti Instant when the stress wave first arrives at the incident end of the specimen (s) tt Instant when the stress wave first arrives at the transmitted end of the specimen (s) tb Instant when the force equilibrium on both ends of the specimen is first achieved (
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