Orientation and strain rate dependent tensile behavior of single crystal titanium nanowires by molecular dynamics simulations

Molecular dynamics simulation was employed to study the tensile behavior of single crystal titanium nanowires(NWs)with1120,1100and[0001]orientations at different strain rates from 10~8s~(-1)to10~(11)s~(-1).When strain rates are above 10~(10)s~(-1),the state transformation from HCP structure to amorphous state leads to super plasticity of Ti NWs,which is similar to FCC NWs.When strain rates are below 10~(10)s~(-1),deformation mechanisms of Ti NWs show strong dependence on orientation.For1120orientated NW,1011compression twins(CTs)and the frequently activated transformation between CTs and deformation faults lead to higher plasticity than the other two orientated NWs.Besides,tensile deformation process along1120orientation is insensitive to strain rate.For 1100orientated NW,prismaticaslip is the main deformation mode at 10~8s~(-1).As the strain rate increases,more types of dislocations are activated during plastic deformation process.For[0001]orientated NW,1012extension twinning is the main deformation mechanism,inducing the yield stress of[0001]orientated NW,which has the highest strain rate sensitivity.The number of initial nucleated twins increases while the saturation twin volume fraction decreases nonlinearly with increasing strain rate.     

含不锈钢纤维机织物电磁屏蔽机理及其效能的仿真研究

依照电磁屏蔽理论,介绍了金属织物电磁屏蔽的机理。在此基础上,利用多物理场耦合分析软件COMSOL Multiphysics,建立三维仿真模型,分析了不同电磁波极化方向、不同半径和不同嵌织间距的奥氏体304不锈钢长丝,在不同辐射频率下对织物屏蔽效能的影响。仿真结果表明,极化方向、半径大小、嵌织间距和频率,对屏蔽织物都有显著的影响,这对不锈钢长丝防电磁辐射织物的开发和设计提供理论依据。     

针对几种元启发式算法的应用性能对比研究

随着智能制造和精益生产的推进,元启发式算法(智能算法)已经在实际工业和生活中得到了广泛应用。然而,由于其自身结构所带来的不确定性,如何针对具体目标快速选择一个高效的特定算法,仍然需要进一步的研究与探讨。为此以具有代表性的NP-hard问题—TSP问题为例,针对典型的元启发式算法:遗传算法、模拟退火算法、禁忌搜索算法和蚁群算法进行了不同维度的实验与对比。并结合算法的不同求解思想,通过对其计算结果和计算过程的定量分析,给出了四种算法的特点与异同,以此来为相关算法的选择、应用以及改进提供基础与参考。     

基于混合优化算法的装配线平衡问题

为求解给定装配线生产节拍、最大化装配效率的装配线平衡问题,根据装配线的特点和平衡优化需求,分析了装配作业顺序、站位数量等因素对装配线站位内作业分配的影响,综合考虑装配线平衡率和平滑系数,建立了装配线平衡问题数学模型,并设计了一种结合遗传算法(Genetic Algorithm,GA)、蚁群算法(Ant Colony Optimization algorithm,ACO)的混合优化算法进行求解。采用遗传算法进行快速随机的全局搜索,并生成信息素矩阵初始分布,利用蚁群算法进行精确求解。最后通过标准案例测试,证明了该混合优化算法具有更高的优化效率,同时验证了算法的可行性和有效性。     

基于精英集聚效应的实数编码小世界优化算法

为了提高小世界算法的高维模型优化性能和降低算法的编码复杂性，提出了一种基于精英集聚效应的自适应实数编码小世界优化算法。该算法借鉴小世界现象进行网络空间搜索，包括随机长连接和局部短连接。为了提高优化性能，首先基于精英集聚效应在长连接中加入分级个体吸引策略；然后根据节点优化优劣在短连接中进行搜索次数及邻域大小的自适应调整。为了降低编码复杂性采用了实数编码。最后通过Markov链理论证明了算法的收敛性。数值测试结果表明，与禁忌遗传算法、基本小世界算法以及禁忌小世界算法相比，该算法在相对误差方面平均降低了30.3%，在收敛速度和稳定性方面分别平均提高了18.2%和13.8%，从而验证了算法的有效性。     

The drying kinetics of kale (Brassica oleracea) in a convective hot air dryer

The effect of air temperature and sample thickness on the drying kinetics of kale was investigated using a convective air dryer at a fixed airflow rate of 1 m/s and drying air temperatures of 30, 40, 50 and 60 °C. The sliced kale leaves were dried in wire trays in 10, 20, 40 and 50 mm thick layers. The drying rate increased with drying air temperature but decreased with layer thickness. The effective diffusivity for 10 mm thick layers was found to increase with the drying air temperature and ranged between 14.9 and 55.9 × 10⁻¹⁰ m²/s. The effect of temperature on diffusivity could be expressed by an Arrhenius type relationship with a high R² of 0.9989. The activation energy of kale was found to be 36.115 kJ/mol. When four drying models were developed using the experimental data the Modified Page model was found to be marginally better than the other models in estimating the drying curve over the experimental temperature range.     

磁粉制动器加载性能试验研究

针对电梯载荷试验替载装置组合加载过程中对磁粉制动器性能研究的不足,文中提出对磁粉制动器加载性能进行试验研究。搭建基于三相异步电机试验平台,对磁粉制动器的加载响应时间、输出扭矩等进行性能试验,试验结果分析得到:磁粉制动器加载响应存在一定的滞后性,加载响应时间为12.5 s,电机转速对磁粉制动器加载响应时间没有影响;磁粉制动器的控制电压在0.3~1.3 V范围内,其输入电压和输出扭矩呈线性关系;当磁粉制动器的控制信号一定时,电机转速越大,磁粉制动器的输出扭矩越稳定。试验研究结果为磁粉制动器应用在电梯载荷试验替载装置中提供了试验依据。     

Compressive response of circular cell polycarbonate honeycombs under inplane biaxial static and dynamic loading. Part I: experiments

The crushing response of a polycarbonate circular cell honeycomb to inplane biaxial loading is analyzed. The study involves a combination of static and dynamic experiments. Static experiments corresponding to several different biaxial loading conditions under displacement control are carried out in two different inplane directions respectively. Dynamic experiments related to various impact forces under inplane biaxial loading in two different mutually orthogonal directions, respectively, are conducted. In the first phase of the response, the material deforms in a uniform fashion. Next, a nonlinear phase caused by the progressive localization of deformation is observed. This phase is characterized by the variation of overall (macroscopic) stiffness. The progressive localization causes the walls of each cell within the localized region to contact each other. These periodic honeycomb materials show different collapsed modes under different biaxial loading histories. Experimental measurements indicate how the magnitude of the collapse load varies and how the stress–strain response changes as a function of load biaxiality. The experimental crushing responses between static and dynamic cases are compared.     

薄壁件铣削加工刀具几何参数优化

针对汽车检具薄壁件铣削变形问题,通过改变铣刀的几何参数建立铣削单因素和三因素四水平的正交实验。利用有限元软件AdvantEdge和ABAQUS分别对铣削加工过程和加工残余应力引起的变形进行仿真,研究不同的刀具几何参数对工件变形的影响。采用田口法分析了刀具几何参数对加工变形的综合影响程度。结果表明:刀具后角对工件加工变形影响的最为显著,螺旋角次之,前角最不显著;获得AA5083铣削的铣刀刀具几何参数组合。通过实验对优化后的刀具几何参数的正确性进行验证,证明该方法是检具薄壁件加工中刀具几何参数优化选择的一种有效的方法。     

电动叉车液压举升装置节能系统仿真研究

为了降低电动叉车液压举升装置能量消耗,采用负载敏感平衡阀驱动叉车臂实现升降功能。建立电动叉车提升装置简图,分析叉车自由提升区和第二提升区运动原理。根据能量回收方程式,推导出液压驱动数学模型和节能效率模型。在不同工况下,采用MATLAB对液压泵输出功率进行仿真。结果表明:在空载或轻载工况下,叉车臂在下降过程中,有负载敏感平衡阀比无负载敏感平衡阀的液压泵输出功率小,最大节约了69 kW;在重载工况下,叉车在上升、静止及下降过程中,有、无负载敏感平衡阀的液压泵输出功率几乎相同。合理设置负载大小,采用负载敏感平衡阀,可以实现能量回收,从而节约能量消耗。