二齿差行星减速器齿轮承载能力的计算

在少齿差行星减速器内啮合传动中,存在多对接近啮合的小间隙齿面于理论啮合点左右,轮齿受力产生的微小变形使得某些对齿面相互接触进入啮合状态。多对轮齿同时啮合,使得传动能力明显提高,而它的力学计算属于超静定问题。本文介绍利用有限元分析软件COSMOSDesignSTAR分别计算一对齿啮合和多对齿啮合的承载差别,来说明二齿差行星减速器的承载能力比起常规算法所得到的承载能力的提高量。     

销齿副齿轮弯曲强度可靠性概率有限元计算

借助于有限元分析软件ANSYS9.0中的Monto-Carlo模拟方法对销齿副齿轮进行了弯曲强度可靠性概率有限元计算。以最大弯曲等效正应力为随机输出参数,得出了最大等效正应力大于指定值的概率、随机响应结果相对于随机输入参数的灵敏度值、确定概率时的等效正应力、最大等效正应力柱状图、输出参数相对于最重要输入参数的散点图以及输入参数与输出参数之间的相关系数。为销齿副齿轮及同类零件的可靠性设计提供了可靠的理论依据和可行的方法。     

Effect of particle size distribution of raw powders on pore size distribution and bending strength of Al2O3 microfiltration membrane supports

To lower the sintering temperature of Al₂O₃ microfiltration membrane support, Al₂O₃ powders with particle size distribution of tri-modal are chosen. The results show that the function of fine Al₂O₃ grains depends on their agglomeration state: if fine Al₂O₃ grains distribute discretely, the bending strength of the support increases along with a slight increase in porosity; however, the aggregated fine grains are harmful to both bending strength and pore size distribution of the support. The bridging of medium Al₂O₃ grains between coarse grains contributes to increase the bending strength, but has less effect on porosity. The addition of medium (and/or fine) Al₂O₃ powder has less effect on the pore size distribution of the support if only coarse Al₂O₃ grain forms the support's framework, which suggests a new way to prepare the support with both high bending strength and high porosity at low temperature.     

折剪机床设计及关键零件的有限元分析

介绍了在小型折弯、剪切两用机床设计：干发中，采用了连杆增力机构和齿轮同步机构，实现了在小缸径单杆液压缸驱动下的增力和滑块运动的同步性。在SolidWorks中建立零件的三维模型，用COSMOSXpress对关键零件进行有限元分析，并根据分析结果优化了零件结构。     

Modulus of elasticity and yield bending stress of coating lubrotec 19985 produced by the metal spraying process

Round bars of 13.6 mm diameter made from low alloy steel were sprayed by hard-coating Lubrotec 19985 under the following spraying parameters: the rotation speed varied from 500 to 900 rpm, the feeding speed from 0.1 to 1.0 mm/rev, and the nozzle tip distance from 100 to 200 mm; the sprayed bars were then subjected to bending test. Depending on the thickness of the produced coating, the modulus of elasticity and yield bending stress of the coating were calculated by applying the bending deflection formula and an equivalent cross-sectional area technique, respectively. The results obtained indicated that the thickness, hardness, yield bending stress, and modulus of the elasticity of coating were varied with the variation in spraying parameters. The optimum spraying parameter was a rotation speed of 700 r.p.m, a nozzle tip distance of 200 mm, and a feed rate of 0.1 mm/rev. This optimum parameter produced an acceptable thickness of 1.14 mm, a hardness of 148 HV, a bending stress of 404.9 MPa, and a modulus of elasticity of 91.47 GPa. The results obtained can also help determine the modulus of elasticity and yield bending stress of the various coating materials when a coated round bar is subjected to the bending test. This paper was recommended for publication in revised form by Associate Editor Youngseog Lee Nabil B. Sada was awarded the B.Sc. degree in Mechanical Engineering in 1969, from Baghdad University, Iraq, and Ph.D. degree in Mechanical Engineering in 1980, from Queen’s University of Belfast, United Kingdom. From 1981 to 1989, Dr. Nabil was a Researcher and Lecturer at State Enterprise for Mechanical Industries, and at the Department of Mechanical Engineering at Al-Mostansyria University in Iraq. From 1994 to 1998, he was a Professor at Department of Mechanical Engineering, Al-Tahadi University, Libya. From 1999 to 2008, he was a Professor at the Department of Mechanical Engineering at Al-Balqa’ Applied University, and at Tafila Technical University, Jordan. Currently, he is a researcher in Canada. Mohammed Al-Nawafleh received his B.S. and M.S degrees in Mechanical Engineering from Leningrad Ins-titute of Textile and Light Industry in 1989. He then received his Ph.D. degree from Sankt-Petersburg State University of Technology and Design, Russia in 1993. From 1997 to 2005, Dr. Nawafleh was a Professor at the Department of Mechanical Engineering at Al-Balqa’ Applied University in Jordan. From 2005 to 2008, he was a Professor at the Department of Mechanical Engineering at Tafila Technical University. Currently, he is a Professor at the Department of Civil Engineering at Al-Hussein Bin Talal University, Jordan.     

Beam to String Transition of Vibrating Carbon Nanotubes Under Axial Tension

State‐of‐the‐art nanoelectromechanical systems have been demonstrated in recent years using carbon nanotube (CNT) based devices, where the vibration of CNTs is tuned by tension induced through external electrical fields. However, the vibration properties of CNTs under axial tension have not been quantitatively determined in experiments. Here, a novel in situ method for precise and simultaneous measurement of the resonance frequency, the axial tension applied to individual CNTs and the tube geometry is demonstrated. A gradual beam‐to‐string transition from multi‐walled CNTs to single‐walled CNTs is observed with the crossover from bending rigidity dominant regime to extensional rigidity dominant regime occur much larger than that expected by previous theoretical work. Both the tube resonance frequency under tension and transition of vibration behavior from beam to string are surprisingly well fitted by the continuum beam theory. In the limit of a string, the vibration of a CNT is independent of its own stiffness, and a force sensitivity as large as 0.25 MHz (pN)^?1 is demonstrated using a 2.2 nm diameter single‐walled CNT. These results will allow for the designs of CNT resonators with tailored properties.     

高阶剪切变形理论下角铺设层合板的大挠度问题

本文根据Reddy的三阶剪切变形理论,导出了该理论下对称角铺设层合板非线性弯曲问题的控制微分方程组,并在四边固支边界条件下,用摄动法对上述微分方程组进行了求解。针对不同的层合板参数进行了大量的数值计算,并与经典弯曲理论下的结果进行了比较,得到一些有意义的结果。     

圆弧齿线圆柱齿轮弯曲失效试验研究

本文通过6对齿轮试件的弯曲疲劳运转试验,分析了圆弧齿线圆柱齿轮几种典型的弯曲失效形式,断齿失效机理及不同因素对轮齿弯曲强度的影响,并提出了提高该齿轮承载能力的措施。     

平板弯曲问题的守恒积分及其应用

将Knowles和Sternberg所发现的弹性静力学中的守恒定律应用到平板弯曲问题中,得到了有关平板弯曲问题的几个守恒积分。同时给出了其对偶守恒积分。最后讨论了这些积分在断裂力学中的应用。