Abstract
With the increase of underground mining depth in coal mines, the distribution of stress fields in deep mining becomes more complex, and the stress localization characteristics are obvious. In order to obtain the local mechanical properties and energy evolution of sandstone, this article is based on the three-point bending experiment and combined with the localized failure theory to explore the evolution law of stress field, deformation field, and energy field of sandstone specimen under tensile stress during the three-point bending experiment. The results show that during the three-point bending test of sandstone, with the increase of the span of the three-point bending test, the peak stress at the characteristic point shows an increasing trend, and the peak stress has obvious regional characteristics. In the vertical direction, the peak stress at the characteristic points in the upper part of the neutral layer is larger, and the peak stress at the characteristic points in the lower part of the neutral layer is smaller. In the horizontal direction, the peak stress at the characteristic points in the near field is higher, and the peak stress at the characteristic points in the middle field and the far field is smaller. The stress field and the deformation field have a good corresponding relationship. The upper far-field peak strain tends to decrease with the increase of the span, and the upper near-field peak strain first decreases and then increases with the increase of the span. The lower near-field peak strain tends to decrease and then increase with increasing span, and the lower far-field peak strain fluctuates with increasing span. The energy field is dependent on the stress field and the deformation field, showing obvious regional characteristics. The energy storage and release capacity of the upper area are higher than those of the lower area. The overall performance of the loading energy storage, rebound energy release, and crack propagation energy release in different areas can be described as far field < mid-field << near field. The near-field energy at different spans presents the characteristics of two stages. When the span is between 140 mm and 150 mm, the near-field energy shows a rapid decreasing trend, and when the span is between 150 mm and 180 mm, the near-field energy presents an obvious increasing trend.
Highlights
With the increase of underground mining depth in coal mines, the distribution of stress fields in deep mining becomes more complex, and the stress localization characteristics are obvious
In order to obtain the local mechanical properties and energy evolution of sandstone, this article is based on the three-point bending experiment and combined with the localized failure theory to explore the evolution law of stress field, deformation field, and energy field of sandstone specimen under tensile stress during the three-point bending experiment. e results show that during the three-point bending test of sandstone, with the increase of the span of the three-point bending test, the peak stress at the characteristic point shows an increasing trend, and the peak stress has obvious regional characteristics
Local stress concentration or large local deformation is the precursor of local failure in coal and rock materials. erefore, it is of great significance to analyze the initiation, propagation, and connection of three-point bending cracks in rocks from the perspective of the local deformation of rocks [3]
Summary
As an inhomogeneous and anisotropic elastic-plastic material, rocks constantly consume energy during the fracture process, resulting in irreversible plastic deformation and forming a process zone [1]. e plastic zone further evolves to form the initial crack, and the crack evolution process can be explored through the characteristics of rock deformation evolution. Domestic and foreign scholars have conducted a large number of three-point bending tests, and the deformation and crack evolution laws in different regions have been studied by Moireinterference, optical microscopy, ultrasonic, acoustic emission, and X-ray detection techniques [4,5,6,7,8], and the local deformation characteristics. Scholars have conducted many three-point bending tests with the help of acoustic emission and other technical means Still, they have not explored the relationship between the local stress field, deformation field, and energy field from the perspective of three-point bending experiments. The acoustic emission test of the surface deformation field of the three-point bending specimen was conducted by a digital speckle measurement system during the three-point bending test. Based on the digital speckle correlation (XTDIC), the evolution characteristics of the surface deformation field of rock samples during damage and fracture were analyzed. e distribution characteristics and evolution law of stress field, deformation field, and energy field in the process of three-point bending test were analyzed
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