Numerical modeling and experimentation of dynamic Brazilian disc test on Kuru granite

A simulation method consisting of a constitutive model, originally developed for numerical modeling of percussive drilling, based on viscoplasticity and damage mechanics and a FEM based numerical technique for simulating the dynamic Brazilian disc test using the Split Hopkinson pressure bar apparatus is presented. The model incorporates the strain rate-dependency via linear viscoplastic hardening/softening laws both in tension and compression. Dynamic Brazilian disc tests were performed on Kuru granite. A linear dependency between the loading rates and the indirect tensile strength of Kuru granite discs was observed in the range from 5 to 20 m/s of impact velocity, corresponding to the sample strain rates from 6.7 to 30 s−1. The experimental results were simulated under the plane stress assumption in order to determine the viscosity parameters, i.e., to find the correct values for the viscosity moduli in tension and compression with which the experimental dynamic (indirect) tensile strength and the compressive contact force levels were matched. Despite the continuum assumption of the modeling approach, the diametrical splitting failure mode of the discs was predicted with a reasonable accuracy. Finally, the plane stress assumption was validated by carrying out a genuine 3D simulation.

► A viscoplastic-damage model for rock is calibrated to predict the dynamic tensile strength of rock under dynamic loading conditions occurring in percussive drilling.
► The calibration involves finding the correct values of viscosity moduli of the model via simulating and experimenting the dynamic Brazilian disc test on Kuru granite.
► Due the indirect nature of Brazilian disc test, the model is also calibrated in compression.
► Linear loading (strain) rate dependency for Kuru granite is observed within the loading rate range 400…1600 GPa/s (6.7…30 1/s).
► The model predicts the diametrical splitting failure mode of Brazilian discs with a reasonable accuracy.