Rock Mechanics
M. Hosseini; A. R. Khodayari
Abstract
The fracture mechanics examines the development and expansion of cracks in solids and how they affect the deformation of materials. The stress intensity factors at the tip of the crack and the critical stress intensity factors or fracture toughness of materials are considered in the relevant criteria. ...
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The fracture mechanics examines the development and expansion of cracks in solids and how they affect the deformation of materials. The stress intensity factors at the tip of the crack and the critical stress intensity factors or fracture toughness of materials are considered in the relevant criteria. There are three main modes of applying forces to a crack including the tensile mode, shear mode, and mixed mode. Mode II fracture toughness, which is also called the shear mode, is an important parameter for investigating the rock behaviors. This parameter is used in many different areas such as mining and tunneling. Several methods have been proposed for determining the mode II fracture toughness. In this work, the Punch-True-Shear (PTS) test, standardized by the International Society for Rock Mechanics, was used to determine the fracture toughness while the confining pressure is present. The studied sample was the Lushan sandstone. In this work, notchd cylindrical specimens were prepared for PTS testing. In order to investigate the effect of confining pressure, some tests were conducted in the presence of the confining pressures of 0, 3, 5, 7, and 10 MPa, and to check the effect of temperature, some tests were conducted under 1, 5, and 10 heating and cooling cycles at 60, 100, and 150 ˚C as well as at the ambient temperature (25 °C). The confining pressure of 3 MPa was used in all the tests to examine the effect of temperature. The analyses results showed that with increase in the confining pressure, the mode II fracture toughness and the fracture energy would increase as well. By increasing the number of heating-cooling cycles, the mode II fracture toughness as well as the fracture energy would decrease leading to a reduced fracture toughness and energy for all the three modes of heating specimens up to 60, 100, and 150 ˚C. The effect of the number of heating-cooling cycles on reducing the fracture toughness and fracture energy was greater than the effect of temperature.
Rock Mechanics
M. Hosseini
Abstract
Temperature has a significant role in many actions performed on rocks. An example would be the effect of temperature on rocks in the burial of nuclear waste, geothermal energy extraction, deep oil well drilling, and fires in tunnels. In addition, due to diurnal/nocturnal as well as seasonal temperature ...
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Temperature has a significant role in many actions performed on rocks. An example would be the effect of temperature on rocks in the burial of nuclear waste, geothermal energy extraction, deep oil well drilling, and fires in tunnels. In addition, due to diurnal/nocturnal as well as seasonal temperature variations, rocks undergo a process of heating and cooling. In the present work, the effect of temperature as well as heating and cooling cycles on the rock properties was studied. The utilized samples included tuff, andesite, and sandstone. In addition to natural samples, concrete was also studied in this research work. The aim of this work was to evaluate the effect of temperature on the tensile strength of rocks and the velocity of longitudinal waves in a single heating and cooling cycle of samples as well as evaluating the effect of the number of heating and cooling cycles on the tensile strength of rocks and the velocity of longitudinal waves. In order to investigate the effect of temperature on the tensile strength of rocks as well as the velocity of longitudinal waves in a single heating and cooling cycle, the samples were heated in a furnace. After cooling the samples, the Brazilian and the sound velocity tests were carried out on them. These tests were conducted at the three temperatures of 100, 200, and 300 °C. In order to examine the effect of the number of heating and cooling cycles on the tensile strength and the velocity of longitudinal waves, the samples were heated up to the temperature of 100 °C and then cooled down in order to reach the room temperature. In this case, the work was conducted in the three modes of 5, 10, and 15 cycles. The test results showed that the velocity of longitudinal waves and the tensile strength of samples decreased but their porosity increased. Reduction in the tensile strength varied in different rocks so that the greatest and lowest reduction in the tensile strength was observed in concrete and andesite, respectively.