Full
JI Dongliang (1992-), male, Ph.D., Lecturer. E-mail: 1065045422@qq.com
Outline
As the depth of resource exploitation in our country increases, power shock disasters occur frequently in underground engineering, which will severely restrict the rapid development of the economy. In the process of strengthening the foundation with fly ash concrete, the strengthened body not only bears static loads but also dynamic loads, forming initial defects such as joints and cracks inside. The development, extension, and penetration of cracks under dynamic loads will further reduce the stability of the strengthened structure. Therefore, it is urgent to deeply study the mechanical properties of fly ash concrete with cracks under dynamic loads.
Dynamic impact tests were carried out with the split Hopkinson pressure bar (SHPB) test system on the samples with different fracture angles. Digital image correlation system (DIC) was used to monitor the deformation of surface strain. Characteristics of the samples with different fracture angles after dynamic impact were compared and analyzed including the dynamic strength, energy dissipation and fractal fracture.
The results show that with the increase of the crack angle, the peak stress-strain presents a typical V-shaped pattern, reaching the minimum value at 30°. With the increase of fracture angle, the initial damage zone also moved from the fracture tip to the middle of the fracture, and then the damage range gradually expanded until the formation of macro failure. The failure modes are tensile failure (0°), shear failure (30°), tension-shear mixed failure (45° and 60°) and collapse failure (90°), respectively. The dissipated energy of the sample firstly increase and then decrease with the increase of the fracture angle, reaching the maximum value at 30°. The process of energy accumulation and transformation in fractured rock mass is characterized by the strain energy density. With the increase of the crack angle of the sample, the fractal value of the sample first increases and then decreases, and reaches a maximum value at 30°, indicating that a higher degree of sample breakage associated with dissipates relatively large energy. Based on fracture mechanics, the analytical solution of stress around the crack is given, and the variation of crack initiation angle, stress distribution and energy dissipation under different crack angles is theoretically explained, which is in good agreement with the experimental measurements.
This paper uses the SHPB and DIC systems to conduct dynamic impact tests on specimens with cracks at different angles, and compares and analyzes the dynamic strength, energy dissipation, and fracture fractal characteristics of specimens with different crack angles after dynamic impact, and gives the theoretical results of the stress around the crack. To provide some theoretical support for the deformation control of cracked concrete mixed with fly ash under dynamic action.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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