In relatively cold environments, the combination of freeze–thaw and steel bar corrosion is a key factor affecting the durability of concrete. The adjustment of the stirrup ratio would change the mechanical performance of surrounding concrete, while the circumferential compressive stress can further improve the bonding performance. Hence, based on eccentrically tensioned specimens, the influence of corrosion of stirrups and freeze–thaw of concrete on bond properties is discussed in this paper. The monotonic pull-out test of reinforced concrete specimens is carried out to study the variation rules of bond strength and slip between steel bar and concrete under the coupling action of corrosion rate, freeze–thaw times and stirrup spacing. Based on the experimental data, the empirical formula for the ultimate bond strength is obtained, and a bond–slip constitutive model is established considering the stirrup spacing, stirrup corrosion rate and freeze–thaw times. Then, a refined finite element pull-out specimen model is established by ABAQUS simulation, and the numerical simulation results are compared with the real test ones, so as to make up for the deficiencies in the test and lay the foundation for further finite element analysis.
To improve the engine-driven performance of propellants, high-energy alloys such as Al and Mg are usually adopted as annexing agents. However, there is still room for improvement in the potential full utilization of alloy energy. In this study, we investigated how to improve combustion efficiency by decorating Al3Mg2 alloy with multilayer graphene and amorphous boron. Scanning electron microscopy and Raman tests showed that decorating with multilayer graphene and amorphous boron promoted the dispersion of Al3Mg2 alloy. The results showed that decorating with 1% boron and 2% multilayer graphene improved the combustion heat of Al3Mg2 alloy to 32.8 and 30.5 MJ/kg, respectively. The coexistence of two phases improved the combustion efficiency of the matrix Al3Mg2 alloy.
In the construction industry, an approach to alleviate the environmental problem is to apply ecological composite materials to the construction field. In this paper, the authors added the recycled aggregate and the rice husks to the concrete and measured the strengths of rich husk recycled concrete (RHRC) with different factors as well as determined the constitutive model. Subsequently, the flexural experiment of RHRC sandwich wall was carried out and analyzed in detail, which proved that it could bear the wind loads in normal use condition by the calculation of the experimental data. Then, the compressive experiment and analyses were conducted similarly. Moreover, the finite element method was applied to study the influence of tie bars on the flexural bearing capacity and to deduce the simplified calculation method of vertical bearing capacity of RHRC walls.
To study the effect of particle size on the internal pore structure of micro/nano energetic materials, three kinds of micro/nano explosives 2,6‐diamino‐3,5‐dinitropyrazine‐1‐oxide (LLM‐105) with different particle sizes were selected as the research objects. The internal pore structure information, including porosity, pore volume distribution and fractal characteristics of micro/nano LLM‐105 were characterized by contrast variation small‐angle X‐ray scattering (CV‐SAXS). The scattering results show that the power‐law index of three samples with different particle sizes is between 3 and 4 in the measured q range (the surface fractal dimension Ds of 200 nm LLM‐105 is 2.16, Ds of 500 nm LLM‐105 is 2.20, and Ds of 3 μm LLM‐105 is 2.76). With the decrease of particle size, the interface between the internal pores and matrix becomes smooth. The pore volume per unit mass of LLM‐105 increases with the decrease of the particle size. The increase of pore volume per unit mass when the particle size decreases from 3 μm to 500 nm is much larger than that when the particle size decreases from 500 nm to 200 nm. The number of 2.5 nm–40 nm internal pores in LLM‐105 increases with the decrease of particle size. Especially for the pores of 11 nm, the number of pores increases most obviously with the decrease of particle size.
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