Abstract
This paper presents an experimental procedure for studying the effects of surface cracks on the mechanical behavior of Balmoral Red granite under dynamic and quasi-static loading. Three different thermal shocks were applied on the surface of the Brazilian Disc test samples by keeping a flame torch at a fixed distance from the sample surface for 10, 30, and 60 seconds. Microscopy clearly shows that the number of the surface cracks increases with the duration of the thermal shock. After the thermal shock, the Brazilian Disc tests were performed using a servohydraulic materials testing machine and a compression Split Hopkinson Pressure Bar (SHPB) device. The results show that the tensile strength of the rock decreases and the rate sensitivity of the rock increases as more cracks are introduced to the structure. The DIC analysis of the Brazilian disc tests shows that the fracture of the sample initiates at the center of the samples or slightly closer to the incident bar contact point. This is followed by crushing of the samples at both contact points with the stress bars.
Highlights
The construction of material models and validation of the simulation results, relies on good scientific understanding of the material behavior as well as experimental data for calibrating the material models
This paper presents an experimental procedure for studying the effects of surface cracks on the mechanical behavior of Balmoral Red granite under dynamic and quasi-static loading
The digital image correlation (DIC) analysis of the Brazilian disc tests shows that the fracture of the sample initiates at the center of the samples or slightly closer to the incident bar contact point
Summary
The construction of material models and validation of the simulation results, relies on good scientific understanding of the material behavior as well as experimental data for calibrating the material models. The dynamic testing of rocks, is challenging, especially with the bar methods, since the material fails at very low strains. The simulations of several repeated impacts of the drill on the same location of the rock surface require understanding of the effects of microcracks formed during the first impact. Percussive drilling occurs at impact speeds of around 5–20 m/s, and each impact causes dynamic loading on the rock. Dynamic material behavior and obtaining numerical data are crucially important for the simulation purposes and material modeling, and for the designing of new and more efficient drills and methods for faster and easier drilling. The experimental setup, data acquisition, and interpretation of the results are presented in details
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