Characterization and Modeling of Rock Impact on Steel Plates

Abstract: The aim of the project was to evaluate different numerical techniques and constitutive models in order to find methods mainly for simulation of rock impacting steel at different velocities. Two different numerical techniques have been analyzed and compared, namely the finite element method (FEM) and the discrete element method (DEM). For the FEM simulations the Johnson-Holmquist ceramics material model was used and for the DEM simulations a method with bonded discrete sphere elements was used.

An experimental method based on a modified Split-Hopkinson pressure bar combined with high speed imaging was used with purpose to measure the impact force when a granite drill core impacted a Hardox steel specimen at different velocities. The experimental method could be used to successfully measure the impact force wave for impact at different velocities.

The same experimental setup was modeled using FEM and DEM and numerical results from simulations could be compared to experimental results. Both FEM and DEM could be used to simulate impact at different velocities but both methods require improvements to be reliable. To be able to simulate impact of arbitrary rock geometries at a range of impact velocities further work is required to find constitutive parameters reliable both at high and low strain rates.

Granite was used as rock material and it is a quite inhomogeneous material. From the experimental results it was concluded that the impact force wave displays large variation. Due to the inhomogeneities in the material this variation was presumed to be present regardless of the experimental method used. A comparison between the force signal and the high speed imaging was performed in an attempt to draw some conclusions about the different wave forms. Some suggestions on how the variation could be reduced by improvements on the experimental setup were presented.

A large scale simulation of bulk flow of a rock mass during the emptying of a tipper was also simulated. In this simulation the pressure field on the tipper was calculated. The rock mass was modeled with both FEM and DEM and the flow behavior from the different numerical techniques was compared. For the rock mass the FEM model had arbitrary rock geometries, the DEM model had only spherical rocks. The calculated pressure field on the tipper was considered to be fairly similar from both numerical techniques.