通讯机构：
[Cailong Ma; Jinjing Liao] A;Authors to whom correspondence should be addressed.<&wdkj&>School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou 510006, China<&wdkj&>Authors to whom correspondence should be addressed.<&wdkj&>Xinjiang Key Laboratory of Building Structure and Earthquake Resistance, Xinjiang University, Urumqi 830047, China<&wdkj&>School of Civil Engineering and Architecture, Xinjiang University, Urumqi 830047, China
摘要：
Plastic concrete is a ductile material with a low elastic modulus (1000-3000 MPa), good flexibility, a and strong ability to adapt to the surrounding soil deformation. Hydraulic concrete mainly serves in a watery environment, so the leaching behavior of plastic concrete is crucial and cannot be neglected. Meanwhile, improving the crack resistance and effect of anti-seepage is also a primary task for cut-off walls. In this paper, in order to investigate the mechanical performance and leaching behavior of plastic concrete, a uniaxial compressive strength test was performed on plastic concrete specimens of a specific age (28 days) and different percentages of replacement cement by single bentonite (40%, 50%, and 60%) and bentonite (30%) together with clay (10%, 20%, and 30%), and the compressive strength, elastic modulus, pH value of the leaching solution, ultrasonic transmit time, electrical resistivity, and calcium ion dissolution concentration of plastic concrete have been evaluated. Moreover, the quantitative relationship between pH value and calcium ion concentration change was built through the electrochemical accelerating leaching method. According to the results, adding 40-60% soil materials can entirely meet the compressive strength (2-7 MPa), elastic modulus (below 3000 MPa), and relative permeability coefficient (below 1 x 10(-7) cm/s) of plastic concrete used for cut-off walls while the compressive strength and elastic modulus of plastic concrete with 30% replacement cement by bentonite would be higher than 7 MPa and 3000 MPa, respectively. The leaching resistance of plastic concrete can be improved by more than 30% by adding bentonite coupled with clay, and three representative zones were observed through SEM and energy spectrum analysis, and Ca/Si molar ratio decreased by 30% after leaching.
关键词：
Red clay;Crack resistance;Lignocellulose;Guar gum;Shear strength;Tensile strength
摘要：
Desiccation cracking is a common problem of red clay under wet and dry conditions. The presence of cracks could reduce soil strength properties, which is the major reason for shallow failure of red clay slopes. This study aims to propose some additives to improve the crack resistance as well as the strength of red clay. To this end, three natural fibers and three natural gels were primarily selected to modify red clay. Desiccation crack tests were conducted to identify the best fiber and gel in terms of crack resistance. Then, direct shear tests and uniaxial tensile tests were performed on the soil specimens modified by the best fiber and gel to determine the optimal dosages regarding strength improvements. The results demonstrated that natural gels reduced the crack resistance of red clay, while natural fibers could enhance the crack resistance. Lignocellulose was the best additive in improving the crack resistance of red clay, and the modified effect was positively correlated with the fiber dosage. Adding 1.5% lignocellulose into red clay could reduce the crack rate from 2.19% to 0.30%, with a reduction of 0.86 times. The tensile strength, shear strength and its parameters of lignocellulose-modified red clay showed a trend of increasing first and then decreasing with increasing lignocellulose dosage. At the optimal lignocellulose dosage of 0.75%, the shear strength and tensile strength were increased by 44.63% and 18.21%, respectively. The strength of red clay modified by both lignocellulose and guar gum was positively correlated with the dosage of guar gum, and the desirable dosage of guar gum was 1.0%. In engineering practice, the wet red clay mixed with 0.75% lignocellulose and grass seeds can be employed as planting soil and is sprayed uniformly onto the slope surface after excavation using a spraying planting machine. To further improve the strength of the planting soil, 1.0% guar gum solution can be sprayed on the soil surface. The findings could provide useful guidance for the protection of red clay slopes.
作者机构：
[Hu, Yongle; Ji, Xixi; Tong, Yonggang; Wang, Kaiming; Zhang, Hao; Ren, Ziyi; Fang, Jingzhong] Changsha Univ Sci & Technol, Coll Automot & Mech Engn, Changsha 410114, Peoples R China.;[Yang, Lingwei] China Aerodynam Res & Dev Ctr, Hyperveloc Aerodynam Inst, Mianyang 621000, Peoples R China.;[Chen, Hui] Changsha Univ Sci & Technol, Sch Civil Engn, Changsha 410111, Peoples R China.;[Liang, Xiubing] Acad Mil Sci PLA China, Natl Inst Def Technol Innovat, Beijing 100072, Peoples R China.
通讯机构：
[Yonggang Tong] C;[Xiubing Liang] N;College of Automotive and Mechanical Engineering, Changsha University of Science and Technology, Changsha 410114, China<&wdkj&>National Institute of Defense Technology Innovation, Academy of Military Science PLA China, Beijing 100072, China
摘要：
Normal strengthening methods through precipitations and deformation obviously enhance the strength of metallic materials while resulting in the sacrifice of ductility, and synergistic improvement of strength and ductility is currently an urgent requirement. Herein we developed a cryogenic deformation combined with an annealing method to fabricate CoCrNiMo0.2 medium entropy alloy, which achieved an ultrahigh strength of 1.8 GPa with synergistic improvement in strength and ductility. Microstructure, mechanical performance, and strengthening mechanisms of the developed alloys were investigated compared with that prepared by the regular room temperature deformation method. It was found that high-density nan-otwins were produced in CoCrNiMo0.2 MEA via cryogenic deformation. Fine grains, hard precipitations, and high volume fraction of nanotwins greatly strengthened the alloy, obtaining a yield and ultimate tensile strength of 1400 MPa and 1800 MPa. Ductility improvement of the developed alloy was mainly attributed to the production of deformation nanotwins due to the lower stacking fault energy, which greatly increases the dislocation storage ability, and thus, the ductility of the alloy was enhanced.(c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.
摘要：
To explore the influence of openings on wind loads and wind speeds in high-rise buildings, the wind flow around three-dimensional (3D) square cylinders with a breadth/height aspect ratio of 1:6 was numerically simulated using the large eddy simulation (LES) method via the Fluent 15.0 platform. The opening measures in the X-direction, Y-direction and both directions were all taken into consideration. Firstly, the inflow turbulence synthesis method and parameter settings for LES were verified by comparing the simulation results of standard square cylinders with those of wind tunnel experiments, and the optimal boundary conditions were determined. Then, the wind speed was extracted and compared with the mean wind speed of incoming flow at the same height to analyze the influence of different opening measures on the wind speed of incoming flow by setting monitoring points in the open holes. Finally, the mechanism underlying the effect of the opening form on wind loads and wind speeds was analyzed from the perspective of time-averaged and transient flow field. The results show that the X-direction openings affect the magnitude and distribution of the surface wind pressures by changing the flow separation and flow reattachment. The narrow tube effect can significantly increase the wind speed, while the Y-direction openings have no obvious improvement effect on the surface wind pressures of the structure. The wind speeds in the open holes are greatly reduced due to the shielding effect, and the wind pressures are also reduced for the Y-direction openings. In the X-direction opening holes, the wind speed at the monitoring point increases, while it decreases in the crosswind open holes. In general, the measure of openings in the X-direction can greatly improve the wind load of the structure compared to openings in the Y-direction, and it can provide a good reference for wind power generation in high-rise buildings.
摘要：
In extreme cold regions, a thermal insulation layer (TIL) is commonly employed to mitigate the detrimental effects of frost heaving forces in tunnels. Optimizing the laying scheme of TIL, specifically minimizing frost heaving forces, holds considerable importance in the prevention of frost damage. This research developed a two-dimensional unsteady temperature field of circular tunnels by using the difference method (taking the off-wall laying method as an example) based on the law of conservation of energy. Then, the frozen circle and water migration coefficient were introduced to establish the relationship between the temperature field and frost heaving forces, and a reliable methodology for calculating these forces under the specific conditions of TIL installation was developed. Then (i) the influence of the air layer thickness of the off-wall laying method, (ii) different laying methods of TIL, (iii) the TIL thickness, (iv) the thermal conductivity of the TIL, and (v) the freeze-thaw cycles on the frost heaving force were investigated. The results showed that the frost heaving force served as a reliable and effective metric for evaluating the insulation effect in tunnels. In order to avoid frost damage in compliance with the design requirements, the insulation effects from various laying methods were established, in descending efficacy order as follows: off-wall laying, double layer laying, surface laying, and sandwich laying. Our findings revealed that the optimal thickness for the air layer in the offwall laying method was 0.10 m. The insulation effect of materials with a thermal conductivity below 0.047 W/(m center dot degrees C) was furthermore found to be good. Under freeze-thaw cycle conditions, it is concluded that to prevent frost damage, the TIL thickness should be the sum of the thickness r1 of the first freeze-thaw cycle without frost heaving forces and an additional reserve value 0.06r1 of the TIL thickness.
摘要：
Abstract: The fatigue cracking of orthotropic steel bridge decks (OSDs) is a difficult problem that hinders the development of steel structures. The most important reasons for the occurrence of fatigue cracking are steadily growing traffic loads and unavoidable truck overloading. Stochastic traffic loading leads to the random propagation behavior of fatigue cracks, which increases the difficulty of the fatigue life evaluations of OSDs. This study developed a computational framework for the fatigue crack propagation of OSDs under stochastic traffic loads based on traffic data and finite element methods. Stochastic traffic load models were established based on site-specific, weigh-in-motion measurements to simulate fatigue stress spectra of welded joints. The influence of the transverse loading positions of the wheel tracks on the stress intensity factor of the crack tip was investigated. The random propagation paths of the crack under stochastic traffic loads were evaluated. Both ascending and descending load spectra were considered in the traffic loading pattern. The numerical results indicated that the maximum value of KI was 568.18 (MPa·mm1/2) under the most critical transversal condition of the wheel load. However, the maximum value decreased by 66.4% under the condition of transversal moving by 450 mm. In addition, the propagation angle of the crack tip increased from 0.24° to 0.34°—an increase ratio of 42%. Under the three stochastic load spectra and the simulated wheel loading distributions, the crack propagation range was almost limited to within 10 mm. The migration effect was the most obvious under the descending load spectrum. The research results of this study can provide theoretical and technical support for the fatigue and fatigue reliability evaluation of existing steel bridge decks. Keywords: orthotropic steel decks; fatigue crack; stochastic propagation; stochastic traffic flow; linear elastic fracture mechanics
