考虑支点变形和摩擦的可倾瓦轴承动力学特性研究

针对球形支点可倾瓦轴承(tilting-pad journal bearing, TPJB)瓦块与支点滑动接触问题,采用紊流雷诺方程、赫兹接触理论和库伦摩擦定律建立了考虑支点弹性力和摩擦力矩的可倾瓦轴承系统非线性动力学模型和分析方法,研究了支点变形和摩擦对水润滑可倾瓦轴承轴心轨迹、瓦块振动响应和最小液膜厚度等动力学特性的影响,揭示了支点半径比和支点摩擦因数对轴承性能的影响规律。结果表明：支点变形可使系统振幅和最小膜厚皆增大;支点摩擦可使系统振幅减小,对最小膜厚影响较小且与动载大小有关;增大支点半径比和支点摩擦因数有利于降低系统振幅;当支点半径比为0.96～0.97、支点摩擦因数为0～0.15时,轴承有较高的承载能力。研究结果对球形支点可倾瓦轴承精确建模和优化设计有参考价值。     

考虑支点变形和摩擦的可倾瓦轴承动力学特性研究EI北大核心CSCD

针对球形支点可倾瓦轴承(tilting-pad journal bearing,TPJB)瓦块与支点滑动接触问题,采用紊流雷诺方程、赫兹接触理论和库伦摩擦定律建立了考虑支点弹性力和摩擦力矩的可倾瓦轴承系统非线性动力学模型和分析方法,研究了支点变形和摩擦对水润滑可倾瓦轴承轴心轨迹、瓦块振动响应和最小液膜厚度等动力学特性的影响,揭示了支点半径比和支点摩擦因数对轴承性能的影响规律。结果表明:支点变形可使系统振幅和最小膜厚皆增大;支点摩擦可使系统振幅减小,对最小膜厚影响较小且与动载大小有关;增大支点半径比和支点摩擦因数有利于降低系统振幅;当支点半径比为0.96~0.97、支点摩擦因数为0~0.15时,轴承有较高的承载能力。研究结果对球形支点可倾瓦轴承精确建模和优化设计有参考价值。     

摩擦因数对摩擦自激振动影响规律的数值分析

摩擦因数的变化对摩擦自激振动的产生和发展具有非常重要的影响,然而,在试验过程中很难对接触面之间的摩擦因数进行精确控制。建立了金属往复滑动试验系统的有限元模型,对金属往复滑动过程中的摩擦自激振动现象进行了瞬时动态分析和复特征值分析,在分析过程中对接触面之间的摩擦因数进行了精确控制。时域分析结果显示,摩擦因数对摩擦自激振动的连续性和振幅有非常明显的影响,对摩擦自激振动的频率影响较小;模态分析结果表明,系统的振动模态随着摩擦因数的增大发生了明显变化。     

刚性弓网系统参数对接触线波磨的影响研究

建立地铁受电弓-刚性接触网1∶1有限元摩擦自激振动模型，通过滑动摩擦关系将弓网系统的法向和切向运动进行动力学耦合。基于摩擦自激振动引起波磨理论，使用复特征值法研究刚性弓网系统参数对接触线波磨的影响。结果表明，当摩擦因数μ≥0.15时，刚性弓网系统都会在频率f=818.01 Hz发生摩擦自激振动现象，这个摩擦自激振动引起刚性接触线波磨。当摩擦因数μ<0.15时，可以显著减轻接触线波磨；当法向接触力F≤110 N或跨距L=6 m时，可以有效缓解接触线波磨；当弓头悬挂扭簧刚度K=100 N·m/rad时，接触线波磨发生的可能性较小。     

干气密封摩擦界面法向接触刚度分形模型

为揭示干气密封摩擦界面的摩擦振动规律,用分形参数表征干气密封摩擦界面形貌特性,根据重新建立的微凸体接触变形方式,以及概率理论建立了干气密封摩擦界面法向接触刚度分形模型。通过与相关实验数据和模型的对比,验证了该模型的合理与正确。对影响法向接触刚度的关键因素进行了数值分析,研究结果表明:法向接触刚度随分形维数、真实接触面积的增大而增大;当接触面积一定时,法向接触刚度随特征尺度、摩擦因数的增大逐渐减小。相比于分形维数、特征尺度对法向接触刚度的影响,摩擦因数的影响相对较小。该研究结果为进一步研究干气密封摩擦振动奠定了基础。     

冲击摩擦及其对弹性涂层冲蚀率的影响研究

将ChenDanian等人提出的弹性斜冲击摩擦模型进行了对称简化,用简化模型分析了粒子对弹性涂层冲击过程中摩擦系数的变化规律及其对涂层冲蚀率的影响;结论指出,在冲击接触的中间时段摩擦系数达到一个平台值(最大值),且有fmax=ctgα0,一次冲击全过程的平均值fp与试验值接近;随着初始入射角α0的增加,摩擦系数降低。将得到的摩擦系数值代入作者提出的冲蚀预估模型进行涂层冲蚀率的计算表明,在初始入射角α0=30°附近,弹性涂层的冲蚀率达到最大值,与实验结果吻合。     

7A52铝合金微动磨损行为研究

利用微动磨损试验机研究7A52铝合金的微动磨损行为,分析不同载荷、振幅、循环次数等参数对摩擦因数和磨损体积的影响,观察分析不同振幅下的磨痕形貌,检测磨痕微区及磨粒的成分组成,探讨其磨损机制.结果表明:7A52铝合金的摩擦因数在不同振幅下的变化趋势不同,微动振幅较大时,实验初期摩擦因数迅速升高,而振幅较小时摩擦因数没有这种现象;磨损体积随着循环次数、振幅、载荷的增加而增加;振幅较小时微动磨损机制主要为磨粒磨损,振幅较大时磨损机制则以黏着磨损和磨粒磨损为主,随着振幅的进一步增加逐渐出现接触疲劳磨损.     

干气密封动静环摩擦界面热弹法向接触刚度分形模型

基于分形理论,根据重新建立的微凸体接触模型,并考虑微凸体弹性变形以及热应力变形,建立了干气密封两摩擦界面热弹性法向接触刚度计算模型,并对其影响因素进行了数值分析。研究结果表明:热法向接触刚度、弹性法向接触刚度均随无量纲真实接触面积、分形维数增大而增大,而随特征尺寸增大而减小,其中分形维数、特征尺寸对弹性法向接触刚度影响较为显著;摩擦因数对热法向接触刚度和弹性法向接触刚度的影响相反,摩擦因数增大,热法向接触刚度变大,而弹性法向接触刚度变小;热法向接触刚度随着转速以线性方式增大。摩擦界面热弹法向接触刚度分形模型的建立与分析,将为研究考虑热效应的干气密封摩擦振动奠定一定基础。     

低频振动对塑性成形表面微观形貌的影响

目的 通过对塑性成形界面施加纵向和法向低频振动,探究不同振动参数对成形过程中表面质量的影响规律。方法 采用自主设计的低频振动发生器完成纵向振动作用下的摩擦实验和法向振动作用下的压缩实验,统计材料表面变形区域的平均粗糙度,评价成形质量。结果 在干摩擦条件下,不同频率（0～50 Hz）的纵向小振幅（0.1mm）振动有利于提高成形界面的表面质量,变形区域的表面粗糙度与频率成反比,但是较大振幅（0.4 mm）的纵向振动会增加接触面的材料磨损,降低表面质量;不同频率（0～50 Hz）和不同振幅（0～0.4 mm）的法向振动均有利于提高干摩擦成形界面的表面质量,在0.2 mm振幅条件下表面粗糙度下降最为明显,振幅超过0.2mm后,增加振幅对提升表面质量的影响不明显。结论 低频振动对成形界面微观形貌影响较大,合理优化低频振动工艺参数可显著提高成形界面的表面质量。     

橡胶-地面石材摩擦性能的研究

基于橡胶摩擦学原理,采用水平拖拉方法在自制的简易摩擦测试装置上进行了橡胶-地面石材的摩擦性能实验,研究了法向荷栽、名义接触面积、静止接触时间对其摩擦性能的影响.结果表明,随着法向荷栽的增大,橡胶一地面石材的静摩擦因数有所减小,但减小的幅度逐渐减小;在同等低法向荷栽条件下,随着名义接触面积的增大或静止接触时间的延长,静摩擦因数均增大,表现出良好的线性相关性;但在同等中高法向荷栽条件下,静摩擦因数与名义接触面积不再符合简单的线性增长关系.     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from     

CNAS Passes APLAC's PTP Review

正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively.