基于有限元的挖掘机动臂性能优化分析

采用有限元分析方法对液压挖掘机的动臂性能进行了优化。以产品的性能为应用目标,通过建立参数化模型并以ANSYS软件为平台,研究了优化设计方法在实际中的运用效果。优化前、后实验结果对比表明,该方法能快速有效地提高产品的设计效率,为同类零件的设计提供参考。     

(AlCrMoNiTi)N_x和(AlCrMoZrTi)N_x薄膜的摩擦特性

采用射频磁控溅射技术在S304不锈钢和纯Cu基体上成功制备出了(AlCrMoNiTi)Nx和(AlCrMoZrTi)Nx高熵合金氮化物薄膜,采用微磨损试验机对两种薄膜的摩擦特性进行了研究。结果表明,(AlCrMoZrTi)Nx薄膜在S304不锈钢和纯Cu衬底上的最小摩擦因数分别为0.182和0.127,最高耐磨寿命为1 200s。在两种衬底上,(AlCrMoZrTi)Nx薄膜的摩擦性能均优于(AlCrMoNiTi)Nx薄膜,其原因主要在于薄膜中Zr的固溶强化效果高于Ni,因而薄膜的摩擦性能得到增强。两种薄膜在S304不锈钢和Cu衬底上的磨损机制主要为磨粒磨损。     

单形替换法动态可视化技术研究

为解决《机械优化设计》课程教学中算法演示的难题,提出了优化算法动态可视化演示的思想。以单形替换法为对象,介绍了单形替换法的算法原理。提出了将单纯形三个顶点坐标值作为可视化演示关键特征变量的处理方法。在此基础上,分析了单形替换法的动态可视化技术原理,包括算法实现、迭代过程存储与演示动画生成等内容。运用VB开发了单形替换法动态可视化教学软件,通过实例演示证明,该软件有助于学习者更清晰的看到算法的求解过程,有效地提高了教学质量。     

Carbon nanotubes array reinforced shape-memory epoxy with fast responses to low-power microwaves

In this study, epoxy shape-memory polymer (ESMP) was infiltrated into the scaffolds of vertically aligned carbon nanotubes (CNTs) array grown by chemical vapor deposition (CVD). In the fabricated CNTs array/ESMP nanocomposite, the CNTs interconnected with each other and a three-dimensional (3D) network of the CNTs was formed. As a result, both thermal conductivity and electrical conductivity of the CNTs array/ESMP nanocomposite were higher than the random CNTs/ESMP composite fabricated by conventional high-speed mechanical stirring. In the random CNTs/ESMP composite, the CNTs aggregated seriously in the matrix. Along the CNTs axis, The CNTs array/ESMP nanocomposite showed a higher modulus and hardness than the random CNTs/ESMP composite, as revealed by nanoindentation tests. Under microwave radiation, the temperature of the CNTs array/ESMP nanocomposite increased more rapidly than pristine ESMP and the random CNTs/ESMP composite. Consequently, the CNTs array/ESMP nanocomposite showed a faster shape recovery speed compared with pristine ESMP and the random CNTs/ESMP composite in their microwave-triggered shape memory behaviors. Especially, the CNTs array/ESMP nanocomposite can recover the deformation fully in response to as low as 60 W microwaves. The presented CNTs array/ESMP nanocomposite with improved mechanical property and fast responses to low-power microwaves may find potential applications in smart devices. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47563.     

Ln3+ (Ln = Eu,Dy) - doped Sr2CeO4 fine phosphor particles: Wet chemical preparation,energy transfer and tunable luminescence

The Sr₂CeO₄:Ln³⁺ (Ln = Eu, Dy) fine phosphor particles were prepared by a facile wet chemical approach, in which the consecutive hydrothermal-combustion reaction was performed. The doping of Ln³⁺ into Sr₂CeO₄ has little influence on the structure of host, and the as-prepared samples display well-crystallized spherical or elliptical shape with an average particle size at about 100–200 nm. For Eu³⁺ ions-doped Sr₂CeO₄, with the increase of Eu³⁺-doping concentration, the blue light emission band with the maximum at 468 nm originating from a Ce⁴⁺ → O²⁻ charge transfer of the host decreases obviously and the characteristic red light emission of Eu³⁺ (⁵D₀→⁷F₂ transition at 618 nm) is enhanced gradually. Simultaneously, the fluorescent lifetime of the broadband emission of Sr₂CeO₄ decreases with the doping of Eu³⁺, indicating an efficient energy transfer from the host to the doping Eu³⁺ ions. The energy transfer efficiency from the host to Eu³⁺ was investigated in detail, and the emitting color of Sr₂CeO₄:Eu³⁺ can be easily tuned from blue to red by varying the doping concentration of Eu³⁺ ions. Moreover, the luminescence of Dy³⁺-doped Sr₂CeO₄ was also studied. Similar energy transfer phenomenon can be observed, and the incorporation of Dy³⁺ into Sr₂CeO₄ host leads to the characteristic emission of ⁴F_9/2 → ⁶H_15/2 (488 nm, blue light) and ⁴F_9/2 → ⁶H_13/2 (574 nm, yellow light) of Dy³⁺. The Sr₂CeO₄:Ln³⁺ fine particles with tunable luminescence are quite beneficial for its potential applications in the optoelectronic fields.     

运动员膳食营养管理研究进展

文章对SCI、中国知网等文献检索网站上发表的有关运动营养学论文进行了系统搜集、梳理以及分析，综述了目前国内外运动员运动膳食营养研究进展，探明了能量、碳水化合物、蛋白质和脂肪的代谢规律与营养管理策略，以期为中国运动营养领域理论发展和运动营养食品研发提供参考。     

Chen氏系统的标度化设计及其硬件实现

为了使混沌系统得到有效的利用,提出了一种基于Chen氏系统的标度化设计方法。对Chen氏系统进行比例变换和微分〖CD*2〗积分变换,并详细分析了标度化Chen氏系统的特性;以标度化系统为模型用普通电路模块搭建标度化Chen氏混沌电路;对标度化系统采用单向单变量耦合替换法,实现驱动系统和响应系统的同步。理论分析与电路实验结果表明该方法可以直接应用于工业生产。     

六面顶压机合成过程中线性卸压机构的设计与应用

为解决六面顶压机合成过程中超高压卸压不平稳和速度慢的难题,对其卸压机构采用自动、线性方式进行设计及优化。基于液压控制理论,使用AMESim软件建立六面顶压机工作模型、控制模型及线性卸压模型;编制4类不同的卸压工艺曲线,基于经典PID(proportion integral differential)控制理论,对线性卸压模型进行仿真计算,并以阀芯半锥角及阀座节流孔直径为变量,得出满足工艺要求的线性卸压方案。对设计的线性卸压机构进行实际测试,实际压力与设定压力曲线的压力偏差绝对值≤0.01 MPa,符合预期设计要求。      

工业纯铁的氮碳钛离子共渗工艺

针对氮、碳二元离子共渗电磁纯铁的渗氮层硬度低、耐磨性差的问题,采用氮、碳、钛三元离子共渗的方法对其进行表面改性处理。结果表明,在相同渗氮工艺下,海绵钛的加入,有效地提高了渗氮层的表面硬度;在520 ℃共渗8 h时,测得渗层硬度最高可达513 HV0.05。但是三元离子共渗降低了纯铁的磁性能,尤以低磁性能降低较多,稍低于GB/T 3656—2008要求,中磁性能与高磁性能仍满足标准要求。     

脱碳层对38CrMoAl钢离子渗氮的影响

对表面残存不同厚度脱碳层的38CrMoAl钢塔形试样进行离子渗氮,借助显微硬度计、光学显微镜、扫描电镜等多种手段,对试样渗速、硬度及渗氮前后的微观组织进行研究。结果表明,在残余的脱碳层里存在较严重的魏氏组织;残余脱碳越严重魏氏组织越多;离子渗氮的渗速随着表面脱碳层厚度的增加先增加后降低;魏氏组织中大量的铁素体为氮原子扩散提供了快速渗入通道及形成大量氮化物的场所,在渗层表面形成大量的鱼骨状、网状、脉状氮化物,数量随着脱碳层的增加而增加,并且不断向渗层深处延伸。38CrMoAl钢表面残存脱碳层虽然有加快渗速的作用,但会增加渗层的不良组织,增加渗层剥落的风险。故38CrMoAl钢制工件做普通调质应适当加大加工余量。