Influence of ECAP on the fatigue behavior of age-hardenable 2xxx aluminum alloy

The fatigue behavior under load control and the mechanical properties of commercial 2011 aluminum as an age-hardenable Al alloy was studied. To estimate the effects of the equal channel angular pressing (ECAP) process, solution heat treatments, and aging on the fatigue life, tests were conducted at four different stages:furnace cooling; furnace cooling plus one ECAP pass; solid solution heat treatment, quenching, one ECAP pass plus aging at peak age level; and the T6 condition. Only one pass was possible at room temperature because of the high strength of the material. The fracture surface morphology and microstructure after fatigue were evaluated by scanning electron microscopy (SEM). The experimental results revealed that the optimum fatigue life under load control, the tensile strength, and the Vickers hardness of the material were interdependent. The optimum fatigue life under load control was achieved by increasing the tensile strength and hardness of the material.     

Damage prediction of 7025 aluminum alloy during equal-channel angular pressing

Equal-channel angular pressing (ECAP) is a prominent technique that imposes severe plastic deformation into materials to enhance their mechanical properties. In this research, experimental and numerical approaches were utilized to investigate the mechanical properties, strain behavior, and damage prediction of ECAPed 7025 aluminum alloy in various conditions, such as die channel angle, outer corner angle, and friction coefficient. Experimental results indicate that, after the first pass, the yield strength, ultimate tensile strength, and hardness magnitude are improved by approximately 95%, 28%, and 48.5%, respectively, compared with the annealed state, mainly due to grain refinement during the deformation. Finite element analysis shows that the influence of die channel angle is more important than that of outer corner angle or friction coefficient on both the strain behavior and the damage prediction. Also, surface cracks are the main cause of damage during the ECAP process for every die channel angle except for 90°; however, the cracks initiated from the neighborhood of the central regions are the possible cause of damage in the ECAPed sample with the die channel angle of 90°.     

多球训练在高校足球脚背内侧踢球技术教学中的应用研究

通过教学实验法对“多球训练”在高校足球脚背内侧踢球教学中的运用进行实证研究,结果表明:在高校足球脚背内侧踢球教学中运用多球训练在心理上可以激发学生的学习兴趣,增强学习动机;在生理上可以持续对肌肉进行有效刺激,有助于技术动作的定型和球感的提高.     

霍尔角位移传感器的磁路设计

霍尔角位移传感器主要结构由霍尔元件、永磁体、屏蔽罩、塑料壳体等组成,其核心是霍尔元件和磁路。根据霍尔元件要求设计磁路,从永磁体表中查找出适合的永磁体,再测试出永磁体的退磁曲线、负载线斜率和工作点,和计算数字对比,得出结论。最后通过实际检验,确定磁路设计的最佳方案。     

有限域上的一类量子码

在Avanti Ketkar等工作的基础上,进一步研究给出了有限域上的另一类类似BCH码的经典码,并证明与该经典码相对应的[[N,K,D]]q量子码和[[N+1,K-1,D+1]]q(q≥2)扩展量子码都存在.在二元域上构造扩展量子码的过程主要采用了偶校验,其运算在内积上进行;在非二元域上构造扩展量子码的过程主要采用了使得行向量各个元素相加为0的方法,并借助了有限域上本原元的性质,其运算在Hermitian内积上进行.研究结论扩展了利用经典码构建量子码的范围,证明了扩展量子码的最小距离为D+1,并给出了有关经典非二元码校验位的构造及其相关纯量子码存在的构造性证明方法.分析表明,[[N+1,K-1,D+1]]q扩展量子码比[[N,K,D]]q量子码更适宜于信息的传递.     

基于FLUENT的喷气织机主喷嘴内流场的三维数值模拟

为研究喷气织机主喷嘴内流道中气流运动特性,利用Solidworks建立主喷嘴内流道的几何模型,并通过FLUENT采用标准κε二方程湍流模型对高压、高速可压缩的气流三维模型进行数值模拟.模拟结果表明,等效温度下的高压理想气流,从进气孔喷入内流道便产生湍流流动,而进入锥形区域后逐渐趋于稳定,并且气流速度在主喷嘴内流道喉部达到最大,同时压强达到最小.通过数值模拟,形象地呈现了喷气织机主喷嘴内流道的流场状况,对优化喷气织机主喷嘴内流道的相关参数具有参考价值.     

利用最小偏向角测量谱线波长

在利用光栅测量谱线波长的实验中,常用自准直法保证光线垂直入射。由于光栅玻璃的两个面都反射,从望远镜中看到的绿十字像是重影像,无法精确调整。分光计可以比较方便的测量相应衍射线与入射线的夹角即偏向角。本文先证明了在斜入射情况下,偏向角存有一最小值,再通过测量最小偏向角来测量谱线波长。     

基于位置内环的骨骼服力控制方法

讨论一种基于位置内环的力控制方法,并将其应用于骨骼服的控制之中。首先,基于系统的静态模型建立骨骼服的位置控制内环,再采用多维力/力矩传感器测量操作空间中人作用于骨骼服的力/力矩信息,构造位置内环的参考输入信号,形成力控制外环,并对人体负荷情况下的蹲起动作进行仿真实验。研究结果表明:该方法无需系统精确的动态模型,就能控制骨骼服跟随人体运动,并保持人体对骨骼服的作用力最小;所设计的控制器是有效的,并对环境变化和负荷变化具有较强的鲁棒性。     

杯形薄壁梯形内齿轮旋压成形机理研究

杯形薄壁内齿轮的旋压成形是旋压技术在应用领域的又一拓展,与传统筒形件流动旋压不同的是,其成形的目的不是材料的整体减薄,而是材料的局部增厚,因而其变形机理十分复杂。论文采用数值模拟和工艺试验相结合的方式,从成形过程中材料的流动入手,对其变形机理进行了研究。研究结果表明：内齿轮轮齿的旋压成形过程,是“镦挤”复合变形;变形分布呈现出周期性,不均匀性和不对称性等特点;轮齿成形受工件转动方向影响,且易出现成形缺陷。     

末次冰期以来东海内陆架沉积反映的海平面变化

对东海内陆架泥质沉积区MD06-3042孔(27°05.4′N,121°24.1′E,水深62m,岩芯长34.1m)样品进行了高分辨率的粒度分析和14C年代测试,重建了末次冰期以来东海内陆架区的海平面及沉积环境的变化.14.0ka左右,海平面已经到达现今海平面下62m等深线的位置,大量沉积物在此沉积.13.0~4.2ka之间,受海流等多种因素影响,少量沉积物在此沉积.4.2~3.2ka之间,现代东海内陆架的泥质沉积主体在该岩芯附近快速堆积.东海内陆架的泥质沉积体由北向南,由内向外逐渐形成,具有阶段性.