摘要：
Examining the impacts of accident characteristics and differentiated built environment factors on accident severity at inherent accident hotspots within cities can help managers to adjust traffic control measures through urban planning and design, thereby reducing accident casualties. In this study, time series clustering was used to identify traffic accident hotspots in Changsha City. Based on the hotspot identification results, Kruskal-Wallis tests were used to select differentiated built environment factors among different accident areas within the city. A severity analysis model for road crashes in Changsha's hotspots, taking into account the built environment, was constructed using a Light gradient boosting machine (LightGBM). In addition, Shapley additive explanations (SHAP) were used to reveal the influences of accident characteristics and built environment factors on accident severity. The results showed that different accident characteristics and built environment factors affect accident severity in different urban accident areas. Factors such as type of accident, visibility, period of time, land use mixing degree, population density, density of commercial places, and density of industrial places showed varying degrees of importance in influencing accident severity, while the overall impact trends remained consistent. On the other hand, transportation accessibility, road network density, landform, and accident location showed significant differences in their impacts on accident severity between different accident areas within the city.
关键词：
Molecular dynamics;Dual -phase Cu -Fe alloys;Fe content;Temperature;Strain rate
摘要：
Design: concept of dual-phase copper alloys was attractive to improve the mechanical performance of Cu. However, a systematic understanding of the interactions between second phase, twins, and dislocations in dualphase copper alloys during deformation was urgent for further strengthening their mechanical properties. Herein, models of dual-phase Cu-Fe alloys with different Fe contents were established and simulated to deeply investigate the interaction between Cu matrix and Fe-enriched phase during deformation as well as the dislocation proliferation and structural changes at the atomic scale. It was found that numerous dislocations and twins were produced in Cu matrix during the deformation process, while grain boundaries of Fe-enriched phases were able to effectively impede the movement of dislocations, resulting in an enhancement of the alloy's strength. Furthermore, new grain boundaries were appeared in the Fe-enriched phase of the dual-phase Cu-Fe alloys at higher strain rates, resulting in a certain grain refinement. With the increasing temperature, the main deformation mechanism of dual-phase Cu-Fe alloys were changed from dislocation slip to grain boundary slip. In addition, the additional Fe content can significantly strengthen the alloys, and the changes in the mechanical properties of dual-phase Cu-Fe alloys during deformation were verified via experiments.
作者机构：
[Xinsheng Wang; Jifeng Luo; Shizhong Wei] Hennan Key Laboratory of Intelligent Manufacturing of Mechanical Equipment, Zhengzhou University of Light Industry, Zhengzhou, 430002, China;[Yang Li; Yueyang Yu] National-Local Joint Engineering Laboratory of Intelligent Manufacturing Oriented Automobile Die & Mould, Tianjin University of Technology and Education, Tianjin, 300222, China;[Yonggang Tong] College of Automotive and Mechanical Engineering, Changsha University of Science and Technology, Changsha, 410114, China;[Honglin Mou; Zhihai Cai; Zhiguo Xing] National Engineering Research Center for Remanufacturing Academy of Armored Forces Engineering, Beijing, 100072, China
通讯机构：
[Zhihai Cai] N;National Engineering Research Center for Remanufacturing Academy of Armored Forces Engineering, Beijing, 100072, China
摘要：
Titanium alloy is an essential material for preparing aerospace engines because of its excellent performance. However, the poor wear resistance of titanium alloy restricts its further development as a critical engine material. This study aimed to use laser cladding and particle enhancement technologies to enhance the surface wear resistance of titanium alloy. (NiCoCr)94Al3Ti3+hBN, (NiCoCr)94Al3Ti3+cBN, and (NiCoCr)94Al3Ti3+hBN + cBN were prepared on the surface of titanium alloy, and the wear resistance mechanism of single-phase self-lubricating particles, single-phase hard particles, and self-lubricating and hard biphasic particles was investigated. The results showed that the microhardness of the biphase-reinforced coating was 1083.8 HV0.5, which was higher than that of the self-lubricating particle-reinforced coating and hard-particle-reinforced coating by 368.4 HV0.5 and 149.8 HV0.5, respectively. The friction coefficient of the biphase-reinforced coating was 0.4208, which was lower than that of the self-lubricating particle-reinforced coating and hard-particle-reinforced coating by 0.0224 and 0.0686, respectively. The wear rate of the biphase-reinforced coating was 0.076 mm3/NM, and the wear resistance of the biphase-reinforced coating was 3.42 and 1.37 times that of the self-lubricating particle-reinforced coating and hard-particle-reinforced coating, respectively. hBN relied on its own decomposition to promote the coating to present a layered unstable structure to achieve a wear reduction effect, cBN relied on its own hardness to resist wear and played a wear-resistant role, whereas biphase-reinforced coating had a hard wear resistance and formed a lubricating film to enhance the wear resistance of the coating. The comprehensive performance of the dual-phase wear-resistant coating reinforced by hard particles and self-lubricating particles was better than that of single-phase wear-resistant coating, providing a reference for developing wear-resistant coating integrating hardness and self-lubrication.
期刊：
Journal of Computational Design and Engineering,2024年11(2):230-252 ISSN：2288-4300
通讯作者：
Lairong Yin
作者机构：
[Peng Zhang; Yuyu Li; Kejun Tang; Lairong Yin; Long Huang; Hongbing Wang] College of Automotive and Mechanical Engineering, Changsha University of Science and Technology , Changsha 410114 Hunan , China
通讯机构：
[Lairong Yin] C;College of Automotive and Mechanical Engineering, Changsha University of Science and Technology , Changsha 410114 Hunan , China
摘要：
Automated tape placement (ATP) is an important automated process adopted for the fabrication of large composite components. Trajectory planning is the key link of ATP, which directly affects the precision and efficiency of the layup process and the quality of final products. Presently, most existing trajectory optimization methods for ATP focus on smooth surfaces. Nevertheless, as commercial CAD/CAM software generally uses NURBS (Non-uniform Rational B-Splines) for modelling, the difficulty of finding the solution and the low efficiency associated with the calculation process are inevitable. The discrete methods provide alternatives for designing layup trajectories, whereas their accuracy is seldom analysed. Furthermore, a path optimization algorithm for eliminating gap problems while preventing wrinkles on discrete models is rarely reported. In this paper, the adjustment of layup trajectories for ATP is considered on triangular meshes. First, the triangular mesh is reconstructed as a Nagata patch to recover the original geometry with good accuracy. Then, a numerical method for tracing desired paths on the Nagata patch set is provided and the computation efficiency is validated. Next, two optimization methodologies are proposed to improve the layup of composite tapes while avoiding wrinkles. Finally, the presented two strategies are examined on a discrete hyperbolic surface and a discrete freeform surface and some of the results are delivered.
摘要：
Developing robust and efficient nonprecious metal-based electrocatalysts toward hydrogen evolution reaction (HER) is a big challenge for green and sustainable energy since insufficient catalytic activity and poor stability of current catalysts cannot meet the application requirements. This work reports a freestanding HER electrode FeNiCuAlMo prepared by arc-melting and chemical dealloying methods. The HER performance firstly improves and then declines with the increase of dealloying time. When the dealloying time is 3 h, the electrode shows optimal catalytic performance. The fabricated electrode is composed of AlMo3 and Al5CuMo2, where micro-sized AlMo3 particles are embedded in cellular dendritic Al5CuMo2. Impressively, it displays excellent HER performance, including a small overpotential of 173 mV at a current density of 500 mA/cm2 and outstanding long-term stability for 100 h of continuous hydrogen evolution at 1000 mA/cm2 in an alkaline electrolyte without obvious attenuation. The intrinsic activity of the electrodes combined intermetallic compounds with hierarchical porous structure provides several effects, including enhanced massive active sites, electrolyte access, electron transport, and fast gas release that contribute jointly to enhancing HER activities. The micro-sized AlMo3 particles provide robust framework for the dendritic Al5CuMo2 active sites center, allowing the exposure of enough active sites and simultaneously maintaining good stability. The highly stable and active electrocatalytic HER property makes it as a promising candidate for practical hydrogen production.
关键词：
White layer;Dark layer;Grinding processes;Forming mechanism;Microstructures;Hardness
摘要：
To establish a systematic cognition of formation mechanisms of affected layers in hardened AISI 52100 steel, the experiments were conducted to measure and characterize the microstructure and properties of the affected layers subject to a varying grinding depth and thermal and mechanical effects at different-levels. It is found that the affected layers can be formed mechanically or thermally depending on whether the mechanically-induced effect predominates the thermally-induced effect, and the 25 mu m is exactly the critical grinding depth of the above two effects. From the novel perspective of thermo-mechanical decoupling, when the grinding depth exceeds 25 mu m, grinding temperature is higher than the nominal austenization temperature (Ac1) of the bulk material, the thermally-induced effect becomes dominate, the thickness of the white layer changes abruptly, and there is an obvious dark layer underneath. When the grinding depth is less than 25 mu m, grinding temperature is lower than Ac1, the mechanically-induced effect becomes dominate, the white layer is extremely thin and no dark layer can be observed. The thermally-induced affected layers are formed mainly by a rapid austenite transformation, accompanied by the fragmentation and dissolution of carbide particles, and the white layer is formed on the ground surface. Meanwhile, the subsurface undergoes tempering subjected to high temperature; this leads to the decomposition of austenite and precipitation of a large amount of cementite. With a continuous dynamic recrystallization, a dark softening layer is formed under the white layer. The mechanical-induced affected layers are formed by fragment and refinement of nano- and micro-structures subject to severe plastic deformation and dynamic recovery.
作者：
Wang, Ziwei;Hu, Lin;Wang, Fang;Lin, Miao;Wu, Ning
期刊：
Sustainability,2024年16(5) ISSN：2071-1050
通讯作者：
Hu, L
作者机构：
[Hu, Lin; Wang, Ziwei; Hu, L; Wang, Fang] Changsha Univ Sci & Technol, Sch Automot & Mech Engn, Changsha 410114, Peoples R China.;[Lin, Miao] China Automobile Technol Res Ctr Co Ltd, Tianjin 300300, Peoples R China.;[Wu, Ning] Ruhr Univ, Inst Traff Engn & Management, D-44801 Bochum, Germany.
通讯机构：
[Hu, L ] C;Changsha Univ Sci & Technol, Sch Automot & Mech Engn, Changsha 410114, Peoples R China.
关键词：
traffic safety;injury severity;intersection;random parameters logit model
摘要：
Examining 1192 intersection car and two-wheeled vehicle collision accidents from the China In-Depth Accident Study (CIDAS) database, this study employs population density heat maps for precise assessment of surrounding population densities at accident sites. The K-Medoid clustering algorithm and silhouette coefficient were used to classify accidents into two distinct groups based on population density. Subsequent application of the random parameter logit model revealed key contributing factors to these accidents in varying population densities. The results show notable differences in factors such as collision direction of two-wheeled vehicles, types of accident conflict, road conditions, and traffic flow, depending on the population density. Based on these conclusions, the research can inform differentiated risk prediction for two-wheeled vehicle accidents at intersections and provide insights for intersection design in various population density scenarios.
摘要：
The DOC (diesel oxidation catalyst), DPF (diesel particulate filter), SCR (selective catalytic reduction), and ASC (ammonia slip catalyst) are widely used in diesel exhaust after-treatment systems. The thermal management of after-treatment systems using DOC, DPF, SCR, and ASC were investigated to improve the efficiency of these devices. This paper aims to identify the challenges of this topic and seek novel methods to control the temperature. Insulation methods and catalysts decrease the energy required for thermal management, which improves the efficiency of thermal management. Thermal insulation decreases the heat loss of the exhaust gas, which can reduce the after-treatment light-off time. The DOC light-off time was reduced by 75% under adiabatic conditions. A 400 W microwave can heat the DPF to the soot oxidation temperature of 873 K at a regeneration time of 150 s. An SCR burner can decrease NOx emissions by 93.5%. Electrically heated catalysts can decrease CO, HC, and NOx emissions by 80%, 80%, and 66%, respectively. Phase-change materials can control the SCR temperature with a two-thirds reduction in NOx emissions. Pt-Pd application in the catalyst can decrease the CO light-off temperature to 113 degrees C. Approaches of catalysts can enhance the efficiency of the after-treatment systems and reduce the energy consumption of thermal management.
摘要：
The controller design for integrated electrohydraulic suspension with leaf spring is a complicated and challenging task, aiming to achieve optimal dynamic performance for heavy vehicles. Considering the hysteresis property of leaf spring, parameter uncertainties and nonlinearity, a novel hierarchical optimization control strategy including upper and bottom controllers is proposed to effectively suppress the vertical vibration of vehicle body. To describe the hysteresis property of leaf spring, a novel resistor-capacitor operator hysteresis model is identified by experiment and optimized by genetic algorithm. Based on hysteresis model, the filter adaptive backstepping control with sprung mass uncertainty is designed as upper controller to generate the desired active force for electrohydraulic actuator. Then, the projection adaptive fuzzy sliding mode control is designed as bottom controller for nonlinear actuator with time-varying fluid parameter to accurately track the required target force. Additionally, a stratified sampling algorithm is investigated to optimize the parameters of hierarchical control strategy for addressing multi-objective optimization issue of electrohydraulic suspension with leaf spring. Finally, the results show that the proposed method has better robustness and effectiveness, and it can ensure ride comfort, safety and optimal performance.
摘要：
Magnetic nanoporous materials represent a new emerging category of magnetic materials for construction of magnetic resonance sensors. In this study, we adopted the metal-organic framework materials, MIL-101(Fe), as the precursor to prepare series nanoporous-carbon-Fe(3)O(4) (NPC-Fe(3)O(4)) composites. Results showed that Fe(3)O(4) were uniformly distributed in MIL-101(Fe) and the size of MNP was precisely tuned at different pyrolysis temperatures, conferring the optimal NPC-Fe(3)O(4)-450°C composite with dramatically improved T(2) relaxivity. The NPC-Fe(3)O(4)-450°C composite was modified with antibodies and antigens, respectively, for detection of aflatoxin B(1) in various food samples with complicated matrix. Range from 0.010ngmL(-1) to 2.0ngmL(-1), extreme low detection limit of 5.0pgmL(-1), and satisfied recoveries were successfully achieved, indicating excellent anti-matrix effect. These findings offer a new dimension to engineer novel magnetic materials with improved relaxivity for simple and easy sensing of food hazards in complicated food matrix without any purification or separation procedures.
摘要：
The challenge for practical application of frame structural optimization had previously been investigated by many works, while the mechanical performance requirements such as the displacement, stress, and stability requirements, were often considered separately within optimization, hindering their practical applications. For this purpose, an integrated topology and size optimization strategy of frame structures, in which the structural weight is taken as the objective with the constraints regarding the displacement, stress, as well as stability, is presented in this paper. Different from former researches, each beam is assigned with a topology variable representing the presence of the beam and a size variable correspond to the cross-sectional geometric properties. To achieve an optimized design with standard members, by cooperating the ordered multi-material SIMP (solid isotropic material with penalization) interpolation with the normalized Heaviside functions, the continuous size design variables are projected onto the discrete standard sizes conformed to standard library. Moreover, the comprehensive measure, including the stress relaxation, the pseudobuckling mode treatment scheme, the aggregation constraint, and varying constraint limit schemes, is employed to deal with the multiple constraints in the optimization model. Then, the sensitivities of the objective and constraint functions with respect to topology and size design variables are derived, respectively, and the proposed integrated optimization problem is solved by a nested optimization algorithm. Finally, several numerical examples are presented to demonstrate the feasibility of the proposed approach.
关键词：
Occupant protection strategy;seat orientation;belt airbag;risk of injury;autonomous vehicle
摘要：
In autonomous vehicle, since that occupants no long need to operate the vehicle, they will have time to relax and entertain or communicate with other people. In order to improve the collision safety of the occupants who move freely and have different seat orientation angles in autonomous vehicle, a protection strategy based on the cooperative control of the rotating seat and belt airbag to avoid occupant injuries is proposed: in the pre-crash phase, the occupant on a rotated seat is repositioned into a close-to-standard frontal facing position, while the belt airbag deploys; in the crash phase, the fully deployed belt airbag cushions and absorbs occupant impact with the support of the occupant's legs to reduce injury. Firstly, the current prediction time for unavoidable collisions in self-driving cars is about 350 ms, therefore, the airbag can be inflated by enlarging the inflation duration to reduce its impact during deployment. Due to the fixed installation position of the dashboard airbag, which cannot accompany the deficiency of seat movement, a new type of belt airbag is designed; Then, the simulation models of +/- 45 degrees and +/- 90 degrees seat orientation were established to study the injury mechanism and kinematic response of occupants with different seat orientations in frontal crashes; Finally, the simulation models of active rotating seat with belt airbag were established to study the kinematic response and injury risk of occupants with rotating seat and belt airbag protection strategy. The belt airbag with a capacity of 65 L developed in this paper could effectively protect occupants in a frontal collision at an inflation time of 200 ms and a total inflation mass of 31.4 g; The occupant safety strategy based on rotating seat and belt airbag can effectively reduce the risk of collision injury of occupants with different seat orientations in autonomous vehicle.
通讯机构：
[Fu, G ] C;Changsha Univ Sci & Technol, Sch Civil Engn, Dept Mech, Changsha, Peoples R China.
关键词：
local-global buckling;piezoelectric cylindrical shells;stepped thickness;buckling control;Hamiltonian system
摘要：
The Hamiltonian system is utilized to establish an accurate buckling solution model for piezoelectric material cylindrical shells with stepped thickness. The critical loads and nonuniform buckling modes are obtained by finding the symplectic eigenvalues and eigensolutions of the Hamiltonian equation. The results show that the transition between local buckling and global buckling can be controlled by an applied voltage. These findings can provide a novel method to control the buckling deformation range and symmetry of cylindrical shells.
摘要：
The calcium fluoride (CaF2) component has excellent light transmission and a high laser damage threshold in the UV band, and thus is a potentially ideal material for high-power laser facility. However, the low-damage surface is difficult to attain via the existing processing technologies due to its brittleness, especially the dissociation property of the (111) surface. We innovatively propose H2O(g) plasma-assisted porous diamond abrasive lapping technology to achieve low-damage and high-precision surface processing of CaF2 component, which means that the CaF2 component is modified first and then the softened modified layer is removed by the porous diamond abrasive lapping. The H2O(g) plasma modification mechanism was elucidated through a combination of molecular dynamics simulation and experiment and comparison with H2O(g) plasma etching. The modification layer including an oxide layer and a phase change layer was produced by adjusting the plasma processing process (power of 25 W and H2O(g) content of 10 ml). Then the modified CaF2 component was lapped by the porous diamond abrasive tool on the ductile domain layer which is more than the modified layer and less than the sum of the modified layer and plastic domain. When the lapping process parameters were 200 rpm platen rotation speed and 20 N lapping pressure, a surface accuracy of 15.34 nm PV, 2.29 nm RMS (phi 1 mm) was obtained. This study provides technical support for the low-damage processing of CaF2 component.
摘要：
This work investigates the electrochemical behavior and discharge performance of Mg-3Al-0.4Ca-0.7Mn alloys with three extrusion ratios (ER) of 10, 16 and 25 as anodes for Mg -air batteries. The results show that the ER16 sample has the lowest corrosion current density and the highest corrosion resistance. The corrosion performance of the ER25 sample is slightly reduced due to the excessive discontinuous second phase leading to elevated selfcorrosion rate. The alloy exhibits higher discharge voltage and stable discharge process with increasing extrusion ratio. Increasing the extrusion ratio has a homogeneous microstructure, the increase in the area fraction of nonbasal oriented grains is conducive to the homogeneous dissolution of the anode and the inhibition of the "chunk effect". The ER25 sample showed the highest anode efficiency, specific capacity and energy density of 55.73 %, 1306.67 mA h g-1 and 1635.947 mW h g-1 at 20 mA cm -2, respectively.
摘要：
Biologically active shells typically exhibit complex mechanical behaviors, with their morphogenesis involving rich symmetry breaking events and non-conservative biological forces. In this article, an accurate buckling solution model of active cylindrical shells is established based on the odd elasticity theory. The tension buckling, non-reciprocal torsional buckling and stress-free active buckling of odd elastic cylindrical shells are reported, which are an anomalous instability caused by odd elastic effects. The result shows that the anomalous buckling of cylindrical shells can only occur in the form of chiral deformation, because the energy required for instability can be obtained based on the odd elastic effects.
摘要：
In this study, the performance of a long-stroke moving-iron proportional solenoid actuator (MPSA) was improved by combining numerical simulations and experiments. A finite element model of the MPSA was developed; its maximum and mean relative absolute errors of electromagnetic force were 4.3% and 2.3%, respectively, under typical work conditions. Seven design parameters including the cone angle, cone length, depth of the inner hole of the coil skeleton, cone width of the armature, inner cone diameter, and initial position of the moving-iron core were selected for developing the model, and the coefficient of the variation in electromagnetic force, nominal acceleration, 95% of the maximum stable output electromagnetic force, and corresponding response time were used as the performance indicators. The constraint relation between each performance indicator and the influence of each design parameter on the performance indicators were revealed using the uniform Latin hypercube experiment design, correlation analysis, and the main effect analysis method. A multi-objective optimization mathematical model of the MPSA was developed by combining traditional surrogate and machine learning models. The Pareto solution set was obtained using the nondominated sorting genetic algorithm II (NSGA-II), and three decision schemes with different attitudes were determined using the Hurwicz multi-criteria decision-making method. The results showed that a strong contradiction exists among the 95% of the maximum stable output electromagnetic force and its corresponding response time and the coefficient of the variation in electromagnetic force. The cone angle considerably influenced the performance indicators. Compared with the initial design, the coefficient of the variation in electromagnetic force was reduced by 54.08% for the positive decision, the corresponding response time was shortened by 15.65% for the critical decision, and the corresponding acceleration was enhanced by 10.32% for the passive decision. Thus, the overall performance of the long-stroke MPSA effectively improved.
