Abstract
To investigate the influence of the fissure morphology on the dynamic mechanical properties of the rock and the crack propagation, a drop hammer impact test device was used to conduct impact failure tests on sandstones with different fissure numbers and fissure dips, simultaneously recorded the crack growth after each impact. The box fractal dimension is used to quantitatively analyze the dynamic change in the sandstone cracks and a fractal model of crack growth over time is established based on fractal theory. The results demonstrate that under impact test conditions of the same mass and different heights, the energy absorbed by sandstone accounts for about 26.7% of the gravitational potential energy. But at the same height and different mass, the energy absorbed by the sandstone accounts for about 68.6% of the total energy. As the fissure dip increases and the number of fissures increases, the dynamic peak stress and dynamic elastic modulus of the fractured sandstone gradually decrease. The fractal dimensions of crack evolution tend to increase with time as a whole and assume as a parabolic. Except for one fissure, 60° and 90° specimens, with the extension of time, the increase rate of fractal dimension is decreasing correspondingly.
Highlights
To investigate the influence of the fissure morphology on the dynamic mechanical properties of the rock and the crack propagation, a drop hammer impact test device was used to conduct impact failure tests on sandstones with different fissure numbers and fissure dips, simultaneously recorded the crack growth after each impact
The application of fractal theory in rock crack propagation makes rock defects such as fissures and joints can be expressed by fractal dimension, which provides a theoretical basis for quantitative study of rock materials from micro-fracture to macro-failure p rocess[30,31,32,33,34,35,36,37,38]
(1) Momentum-impulse equilibrium relationship In drop hammer impact test, the gravitational potential energy was converted into kinetic energy when the hammer dropped
Summary
To investigate the influence of the fissure morphology on the dynamic mechanical properties of the rock and the crack propagation, a drop hammer impact test device was used to conduct impact failure tests on sandstones with different fissure numbers and fissure dips, simultaneously recorded the crack growth after each impact. Based on the analysis of the dynamic mechanical properties of rock materials under different fissure forms and the evolution characteristics of the whole process of crack propagation, the energy transfer law between the test device and sandstone specimens during the dynamic impact process is proposed.
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