• Saksala, Timo
• Kuokkala, Veli-Tapani
• Mardoukhi, Ahmad
• Hokka, Mikko

Abstract

The tensile strength of rock-like materials is considerably lower than their compressive strength. Therefore, it is more favourable to break the rock using tensile loading. However, the mechanical response of a rock depends on various factors such as grain size, mineralogy, texture, testing condition, etc. Therefore, to gain understanding of the mechanical behavior of rock materials, a material model capable of accounting for these variables seems necessary. This paper presents a numerical and experimental investigation on the mechanical response of heterogeneous rock, Baltic Green granite, under dynamic loading.<br/>Brazilian disc samples of the studied rock were prepared with the diameter of 40.5 mm and thickness of 21 mm. The Split Hopkinson Pressure Bar (SHPB) used in this work consists of an incident and a transmitted bar with the length of 1200mm and a diameter of 22mm made of AISI 4340 steel. The striker bar of the same material with the length of 300 mm was used to create the impact. The tests were conducted at three different impact speed of 5 m/s, 10 m/s, and 15 m/s. At the impact speed of 5 m/s, half of the tested samples did not break and the tensile strength of the fractured samples showed the average value of 13.27 ± 3.7 MPa. As the impact speed was increased to 10 m/s, the rock showed more consistent behavior and the tensile strength was increased to 23.02 ± 3.4 MPa. At the impact speed of 15 m/s, the recorded average tensile strength was 22.34 ± 3.7.<br/>The Brazilian disc tests were simulated numerically using a material model for rock implemented with polygonal finite elements. The material model is based on the combined damage-viscoplasticity approach where the stress states leading to inelastic deformation and damage are indicated by the Mohr-Coulomb failure criterion with the Rankine criterion as a tensile cut-off. The rock mineral texture is represented as random clusters of polygonal finite elements resulting in a mesomechanical description of rock heterogeneity. The equations of motion are solved with an explicit time marching scheme. The simulation results demonstrate that the present approach can capture the salient features of the heterogeneous rock under dynamic loading. <br/>

Topics

• impedance spectroscopy
• mineral
• cluster
• grain
• grain size
• simulation
• strength
• steel
• texture
• random
• tensile strength