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Experimental techniques of SHPB for calcareous sand and its dynamic behaviors

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Abstract

This paper conducted 11 split Hopkinson pressure bar (SHPB) tests on the calcareous sand sampled from a calcareous reef in China and silica sand sampled from Fujian Provence of China. The relative density is 90%. The strain-rate history, strain history, and stress-strain curves were obtained for sand specimens with three thicknesses including 10 mm, 30 mm and 50 mm. It is found that test error can be reduced by standard procedure in sand preparation. The stress equilibrium and constant strain rate can be achieved by changing the thickness of specimen, the length of striker and the pulse shaper. With an identical relative density and loading condition, the volumetric modulus and shear modulus of calcareous sand is approximately 10% of the silica sand; and the strength of the calcareous sand is approximately 30% of the silica sand. Therefore, the results of existing silica sand can not be directly applied to calcareous sand because of their large discrepancies. © 2018, Editorial Staff of EXPLOSION AND SHOCK WAVES. All right reserved.

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... Because stabilized soil belongs to the low wave impedance material, the application of strain gauge cannot capture an effective signal of transmitted wave. Currently, the semiconductor strain gauge technology has been widely applied in SHPB tests to obtain an effective signal of transmitted wave of low wave impedance materials [33][34][35][36]. ...
... With further increase in fly ash content, the free swelling ratio and volume shrinkage ratio of stabilized soil changed gently. e reduction of swellingshrinkage properties due to the influences of the generation of hydration products inside stabilized soil and the cation exchange reactions between soil particles and fly ash [9,21,23,35]. e principle of cement stabilization is similar to the above explanations. With the addition of more cement or fly ash into stabilized soil, the unreacted cement or fly ash particles kept inside stabilized soil are the main reason of the gentle variation phase in Figures 5 and 6 [38]. ...
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The purpose of this article is to evaluate the influence of basalt fiber content on the static-dynamic mechanical properties and microstructure of cement-fly ash-stabilized soil. The optimum mixed contents of cement and fly ash were obtained from the results of a series of physical and mechanical experiments. Based on the optimum mixed contents of cement and fly ash, the static-dynamic mechanical performances and microstructure of cement-fly ash-stabilized soil reinforced with basalt fiber were studied by means of the unconfined compression test, dynamic compression test (namely, SHPB test), and SEM test. The results demonstrated that the addition of basalt fiber in cement-fly ash-stabilized soil significantly enhanced the static-dynamic mechanical properties of stabilized soil. With basalt fiber content varying from 0% to 1.2%, the unconfined compressive strength, dynamic compressive strength, dynamic increase factor, and specific energy absorption of stabilized soil showed an upward trend first and a downward trend subsequently. The unconfined compressive strength, dynamic compressive strength, and energy absorption ability have a maximum improvement under the optimum basalt fiber content of 0.6%. In addition, the inclusion of basalt fiber can change the failure pattern of cement-fly ash-stabilized soil. The fractal dimension of broken fragments decreased gradually with the increasing basalt fiber content and increased correspondingly with the increasing impact loading pressure. With the basalt fiber content of 0.6%, a stable internal space structure produced inside stabilized soil. However, there are many fiber-fiber weak interfaces that appeared inside stabilized soil under the basalt fiber content of 1.2%. The microstructural observations can be considered as the good interpretations to verify the macroscopic mechanical characteristics.
... Thus, it is easy to collect extremely weak transmitted waves using the semiconductor strain gauge. The technology of a semiconductor strain gauge is widely used to acquire the transmitted waves of low wave impedance materials in SHPB tests, such as porous materials (Liu et al. 1998), frozen soil (Ma 2010;Xie et al. 2014), lightweight foam concrete (Yuan et al. 2014), cement-soil , and calcareous sand (Lyu et al. 2018). Based on the aforementioned studies, the semiconductor strain gauge is mounted on the transmitted bar to acquire transmitted waves, and the strain gauge is mounted on the incident bar to record incident and reflected waves. ...
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An experimental study was performed to investigate the fragment distribution, fractal dimension, and energy dissipation of stabilized soil subjected to impact loading. Dynamic uniaxial compression tests on cement–fly ash–stabilized soil with different sand contents (S = 0%, 8%, 16%, and 24%) were conducted using a 50-mm-diameter split Hopkinson pressure bar (SHPB) under 0.3, 0.4, and 0.5 MPa gas pressures. Then the experimental results were analyzed on the basis of fractal theory and energy dissipation principles. Experimental results showed that the average size of broken fragments decreases rapidly as the gas pressure increases from 0.3 to 0.5 MPa. In addition, the average size of broken fragments also indicates a decreasing trend with increases in sand content. The distribution of broken fragments obtained from SHPB tests has a fractal characteristic. The fractal dimension of impact fragmentation exhibits an increasing trend with increasing sand content, and it increases linearly when the gas pressure increases from 0.3 to 0.5 MPa. Moreover, the dynamic compressive strength can be enhanced significantly by adding 8% sand to stabilized soil, and the dynamic compressive strength of stabilized soil increases in a quadratic function with increases in fractal dimension. Based on energy dissipation analysis, it is easily observed that the energy dissipation density linearly increases with increases in gas pressure; moreover, it first increases and then decreases as the sand dosage increases from 0% to 24%. The addition of 8% sand is regarded as the optimum content to obtain a preferable energy absorption capability of stabilized soil with sand. In addition, with an increase in the fractal dimension, the energy dissipation density presents a logarithmically increasing tendency. The greater the energy dissipation density, the more efficiently the cracks propagated and became connected, the more severe the impact fragmentation, and the larger the fractal dimension obtained. Finally, an empirical equation is proposed to further describe the variations of energy dissipation density versus fractal dimension and dynamic compressive strength.
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