关键词： Ductile iron   Ausferrite   As-cast   ADI   Section size   Engineered cooling  

摘要： The present research work studies the effect of section size, holding temperature and time on the microstructure and mechanical properties of as-cast ausferritic ductile iron. To that aim, Y block standard samples of 12.5 and 25.0 mm thickness were produced through a controlled cooling process. The holding temperatures of 300 degrees C and 400 degrees C were studied. The transformation time was changed in the range of 10-180 min. Furthermore, interrupted cooling experiments on the temperature range of 550 degrees C to 300 degrees C were performed to reveal the ausferritic nose. The experimental results indicated that for a holding temperature of 300 degrees C, an effect of the section size is noticed due to the cooling rate differences before the temperature arrest, while for a holding temperature of 400 degrees C no significant change on the microstructure evolution was observed. Besides, at the studied temperatures of 300 degrees C and 400 degrees C, and holding times of 80 and 65 min, respectively, after the beginning of the ausferritic reaction, the microstructure and the mechanical properties remained constant. The low cooling rate (air cooling) from the early shake out, to the temperature arrest, allowed the formation of some upper acicular ferrite during the cooling process from the ausferrite formation start temperature (defined for the considered alloy around 550 degrees C) down to the holding temperature, even for low temperatures (300 degrees C).

关键词： Muscle  

摘要： Muscle contractions produce reiterated cytoplasmic mechanical variations, which potentially influence nuclear mechanotransduction, however information regarding the dynamics of muscle nuclei (myonuclei) in the course of muscle contraction is still missing. Towards that end, a minimal constraint device was designed in which intact liveDrosophilalarva is imaged, while its muscles still contract. The device is placed under spinning disc confocal microscope enabling imaging of fluorescently labeled sarcomeres and nuclei during muscle contraction, without any external stimulation. As a proof of principle we studied myonuclei dynamics in wild-type, as well as inNesprin/klarmutant larvae lacking proper nuclear-cytoskeletal connections. Myonuclei in control larvae exhibited comparable dynamics in the course of multiple contractile events, independent of their position along the muscle fiber. In contrast, myonuclei of mutant larvae displayed differential dynamics at distinct positions along individual myofibers. Moreover, we identified a linear link between myonuclear volume and its acceleration values during muscle contraction which, inNesprin/klarmutants exhibited an opposite tendency relative to control. Estimation of the drag force applied on individual myonuclei revealed that force fluctuations in time, but not the average force, differed significantly between control andNesprin/klarmutant, and were considerably higher in the mutant myonuclei. Taken together these results imply significant alterations in the mechanical dynamics of individual myonuclei in theNesprin/klarmyonuclei relative to control. Such differences provide novel mechanical insight intoNesprinfunction in contractile muscles, and might reveal the mechanical basis underlyingNesprin-related human diseases.

关键词： Nanowires   1D TMMs   Mechanical behavior   Molecular dynamics   Tensile test   Phase transformation  

摘要： As a new class of one-dimensional (1D) transition-metal monochalcogenides (TMMs) nanowires (NWs), the recently synthesized MoS NWs exhibit potential applications in two-dimensional integrated circuit. However, their mechanical behaviors remain almost unexplored. In this paper, the mechanical behaviors of MoS NWs under tensile loading are studied by classical molecular dynamics simulations together with first-principles calculations. A novel phase transformation is observed in the MoS NWs when the strain applied to them is larger than a critical value, which results in tension-induced hardening in their tensile modulus. Due to the existence of phase transformation, a complicated mechanical response is observed in MoS NWs during the entire loading process, which successively experiences the linear, plateau, stress hardening and fracture stages. The influence of various factors including the strain rate and temperature on the mechanical properties of MoS NWs such as phase transformation, Young's modulus, fracture strength and fracture strain are also examined. The mechanical properties of MoS NWs obtained in this paper will be beneficial to their future applications in the semiconducting field. It is also expected that the results of the tension-induced phase transformation and its influence on the material properties observed in the present MoS NWs can be further extended to other 1D TMMs such as MoTe and SnSe NWs, since these 1D TMMs are found to possess the similar structure.

关键词： 运动力学   机械结构   设计   应用  

摘要： 运动力学主要包括许多机械原理,在许多机械设计过程中,往往要利用这些机械原理来保证设计的科学性。特别是机械设计和静态力学的概念在过去已得到广泛应用,但在实践中,机械设备往往是一个动态的运动过程,这是在相应的动态的机械设备结构设计过程中更重要的研究和应用。因此,本文从机械构造设计中运动力学的应用方面入手,对其作了具体的分析和研究。

关键词： Fe-Zr intermetallics   Amorphous alloys   Crystallization kinetics   Nanocrystalline alloys   Mossbauer spectroscopy  

摘要： Devitrification of mechanically alloyed amorphous Fe70Zr30 at. % compound consists on a two-step process: amorphous -> amorphous + bcc Fe + Fe2Zr -> Fe2Zr + Fe23Zr6. This sequence is inferred from the evolution of the Mossbauer spectra, the thermomagnetic experiments and the X-ray diffraction (XRD) patterns. Hyperfine parameters for both intermetallics have been obtained from Mossbauer spectroscopy in correlation with the phase identification from XRD results. The broadening of the stable compositional range of Fe2Zr intermetallic above 1000 K is responsible for a strong dependence of the phase fractions on heating and cooling rates. Despite the overlapping of the two processes involved in the devitrification, the individual Avrami exponents of each one have been estimated. (C) 2020 Elsevier B.V. All rights reserved.

关键词： 悬臂结构   风机   齿箱   转子动力学  

摘要： 以某风机-齿箱系统为研究对象,研究悬臂结构旋转机械转子动力学计算方法。研究结果表明:通过在计算中增加虚拟轴段,有利于不平衡响应分析,解决了以往处理方法接合轴段混合材质无法精确建模、稳定性分析无法准确施加刚度阻尼的问题,并可进一步提高计算精度。

关键词： 矿山机械   压力传感器   液压泵站   旋挖钻机   液压系统   动力传递   轰鸣声   钢铁巨人  

摘要： 钻头旋转,深入地下,机器轰鸣声中,一台旋挖钻机正在开足马力进行工作。从采矿到选矿,旋挖钻机、挖掘机、起重机等一系列的矿山机械如同一个个钢铁巨人战斗在矿场一线。正所谓"人是铁饭是钢",这些钢铁巨人同样需要稳定而强大的动力。由于液压系统在动力传递中具有用途广、效率高和构造简单的优势,矿山机械通常会利用液压泵站来满足其对动力提供和润滑的需求。

关键词： 工程机械   动力系统胶管   选型设计  

摘要： 工程机械作业工况复杂多变,动力系统胶管的性能对整车的可靠性起着关键作用,若选型匹配或安装存在问题,可能会导致发动机出现严重故障。因此,工程机械动力系统胶管的正确选型设计至关重要,需要针对不同使用环境和输送介质,合理匹配胶管的结构和安装。

关键词： GaN   Nanoindentation   Temperature   MD simulation   Deformation   Mechanical properties  

摘要： A series of three-dimensional molecular dynamics (MD) simulations was performed to investigate the effect of temperature on the nanoscale deformation behaviour and mechanical properties of c-plane monocrystalline gallium nitride (GaN) under nanoindentation. Simulation results showed that the atomic displacement and strain increased with increasing temperature. Thus, the nucleation and propagation of dislocations in the main slip systems were promoted to intensify the plastic deformation of GaN crystal. Increasing the temperature also contributed to the increase in local phase transition from the wurtzite crystal structure (B4-GaN) to the zincblende crystal structure (B3-GaN) and a very evident amorphization of GaN in the indentation zone. Based on the analysis of the load-depth curves, it was found that both the hardness and Young's modulus decreased as the temperature increased. This work can enrich the atomic-level understanding of the effect of temperature on the mechanical response of monocrystalline GaN when subjected to the external loads.

关键词： 位置控制   机械臂   动力学函数   反演滑模控制方法   转矩到位置转换方法   逆动力学  

摘要： 机械臂的位置控制准确度有利于提高机械臂工作的可靠性,为了提高机械臂工作过程中对位置控制的平稳性、快速性、准确性和鲁棒性,设计了一种基于逆动力学的机械臂鲁棒位置控制方法。通过对机械臂的电机系统进行分析,获取电机系统的动力学函数。利用转矩到位置转换方法和反演滑模控制方法,设计了一种逆动力学控制器,通过将滑模控制方法与反演控制方法相结合,形成反演滑模控制方法,获取电机转矩控制函数,以提高系统的鲁棒性能。利用转矩到位置转换方法,将获取的电机转矩与电机的当前位置信息相结合,用以求取机械臂的位置控制量,以实现对机械臂的位置进行快速、稳定、准确的控制。利用Matlab/Simulink软件对所设计的机械臂位置控制方法进行了实验验证。验证结果表明:所设计方法不仅能够快速、稳定、准确地对机械臂的位置进行控制,而且设计方法还具有较强的鲁棒性能,能够适应多种激励信号产生位置控制信息。