Stability analysis of four bar mechanism. Part I— With the assumption that damping is absent

With increasing machine speed, rigid link assumption is no more valid, hence, links of the mechanism are subjected to vibration. Stability analysis of a vibrating system gives the speeds at which the system response is unbounded. It is necessary to avoid these speeds or to provide sufficient damping for better performance of the system. This paper presents the theoretical work done for stability analysis, which is simple and can be extended to any mechanism in general. It gives the speed ranges, in which response is unbounded, and presents the study of the response at various speeds for undamped system.     

Lubrication of carbon fibre-reinforced polymers : Part II—Organic fluids

A variety of organic fluids, including mineral oils and synthetic lubricants, are shown to be effective boundary lubricants for carbon fibre-reinforced polymers sliding against stainless steel. The wear rates of the composites in some fluids are extremely low, and scanning electron microscopy and pyrolysis-gas chromatography show that low wear is associated with the development of films on the steel counterface. These films appear to be mixtures of lubricant and resin from the composite matrix. The wear rates of epoxy/Type II carbon fibre composites in aircraft hydraulic fluids are generally much less than those of many metal combinations, and the composites therefore show promise as replacements for metals in lubricated systems.     

Stability of a flat arch subjected to deterministic and stochastic loads taking into account nonlocal damping

In the example of a flat arch, a problem of vibrational stability of systems subjected to deterministic and stochastic loads is considered taking into account the geometric nonlinearity and nonlocal damping of a material, which is characteristic of certain types of composites and nanomaterials. To study the stability of arch motion within the deterministic statement of the problem (stability in the sense of Lyapunov) and the stability in the almost certain stochastic statement, a method is used which is based on the calculation of the maximal Lyapunov’s exponent. The influence of damping and loading parameters on the degree of system stability is analyzed.     

类四杆五杆机构连杆曲线的变化规律

类四杆五杆机构连杆曲线的变化规律张旭滨（渤海铝业有限公司０６６０００）贲宏艳刘葆旗（燕山大学）１引言类四杆五杆机构就是把铰链四杆机构的某一个杆ａ截成两个杆，并用转动副相联，较短的一个杆称为调节杆ｅ，较长杆为ａ′，且ｅ／ａ′≤０．２５，ｅ和ａ′的传动...     

假肢膝关节四杆机构的优化与仿真

从满足人体运动过程中假肢与人体的协调性出发,对假肢膝关节部位的构型进行选取,并对该机构进行了运动学分析;针对个人膝关节瞬心轨迹曲线,提出该机构尺寸参数的优化数学模型,对该机构的参数进行优化,使目标函数中机构瞬心坐标与人体膝关节瞬时转动中心理想值之差最小,即该机构的实际瞬心轨迹与理想的膝关节瞬心轨迹相接近,满足人体下假肢膝关节机构协调性的设计要求,通过Matlab优化工具箱进行优化计算并获得机构模型,又应用AD-AMS对机构模型进行运动学仿真,验证优化结果的可用性。     

On the stability of columns under stochastic loading taking into account nonlocal damping

Using an example of a column clamped at both ends, the stability of columns made of a material characterized by nonlocal damping is investigated. The column is subjected to axial forces that are deterministic and randomly vary in time. In the deterministic case, the stability is understood in Lyapunov??s sense; in the case of the stochastic formulation of the problem, the almost sure stability is considered. In either case, the method of the top Lyapunov exponent is used to analyze the stability.     

Coating thickness effect on initial wear of nitrogen-doped amorphous carbon in nano-scale sliding contact: Part II—theoretical modeling

This is the second paper of a two-part report. In the first paper, empirical data on the wear particle generation in carbon nitride coatings subjected to repeated sliding contact with a spherical diamond counter-face is reported. The effect of coating thickness on the wear particle generation is also discussed in the first paper. In this paper, a simplified theoretical expression, combining the Coffin-Manson equation with the analytical solution of a proposed elastic perfectly-plastic indentation model, is introduced. The expression successfully correlates critical number of friction cycles for wear particle generation N_c to coating thickness h, contact pressure P and radius of spherical asperity on the tip of the diamond pin R. With this expression, the lifespan of sliding components can be predicted.The theoretical results computed for diamond pin with a specific asperity radius value of 250 nm were compared with the experimental results reported in the first paper. The theoretical model successfully predicts the maximum lifespan of a component, N_c, in repeated sliding applications. The influences of various contact pressures and asperity radii on the maximum lifespan were also assessed using the model.     

Synthesis of function generating spherical four bar mechanism for the six independent parameters

This study deals with the function generation synthesis of spherical four bar mechanism for six independent construction parameters φ₀, ψ₀, α₁, α₂, α₃, and α₄ by giving six or more design points with respect to the methods that are used in synthesis procedure. Quaternion algebra is used to derive the objective function of spherical four bar mechanism by following some rotational sequences. Three different methods as interpolation approximation, least squares approximation and Chebyshev approximation are used during synthesis procedure. During the consecutive trials in Chebyshev approximation, a new approach is taken to renew the design points φ_i by plotting the graph of the objective functions derivative and taking the roots of it as new design points with two boundary points. Separate examples are given for each section and the results are tabulated. Discussions about the study and comparisons between the used methods are given at the end of the study.     

Scuffing — a review: Part 2: The mechanism of scuffing

Surface films and experimental evidence of scuffing in discs and gears are discussed, and the importance of hydrodynamic and boundary lubrication mechanisms have been analysed. The breakdown conditions of these mechanisms and thermal instability work are summarised.     

四位置铰链四杆机构综合与分析的可视化软件系统

开发了一种刚体导引四位置铰链四杆机构综合与分析的可视化软件系统。主要功能有：一、任意给出四位置已知参数,计算出圆心与圆点曲线坐标,绘出圆心与圆点曲线图;二、在曲线图上任意选取两组对应点组成机构,并输出机构参数、绘制出机构图;三、自动判别机构类型,进行机构运动模拟演示;四、对综合的机构或任意给定的已知机构进行运动分析,并绘出连杆轨迹曲线和机构传动角曲线图;五、对机构进行优选,从传动角、机构类型、连杆轨迹及杆长比等方面对机构进行逐一判别,指出具有顺序缺陷、分支缺陷与回路缺陷的机构,筛选出合格的机构。     

Virtual reality system of manned maneuvering unit taking into consideration the disturbance from an astronaut''s limbs

This paper describes a manned maneuvering unit (MMU) virtual reality system. Based on the dynamics/kinematics model of an astronaut equipped with an MMU, a disturbance model of the astronaut’s arms under zero gravity conditions is developed. After measuring three initial-position information, the astronaut’s arms tracking information is inputted by some tracker setting on an operator using real-time emendation and correction. Finally, the paper presents two different results between loading and unloading the disturbance model within the progress of simulation. From the different results, we find that the motion of an astronaut’s arms has greater influence over space walking with the same control mode. The MMU virtual reality provides a new method for the simulation of real space walking, and also a perfect method for developing prototype MMU. __________ Translated from Journal of Shanghai Jiaotong University, 2005, 39(1) (in Chinese)     

投影法作铰锭四杆机构的动态静力分析

针对铰链四杆机构动态静力分析，这里提出了一种新的解析法－－投影法，此方法不仅有解析法计算精度高特点，而且还保留了图解法直观性强的优点。     

An investigation into upheaval buckling of buried pipelines—II. Theory and analysis of experimental observations

This paper and its companion describe an experimental study of some aspects of the upheaval buckling of buried pipelines by means of a small-scale model apparatus. After a discussion of relevant literature, the experimental apparatus is described in detail: it involves a thin-walled steel pipe of diameter 6 mm and length 5 m, buried in a bed of artificial soil. The horizontal and vertical profiles of the pipe are measured by an electrical remote-sensing device. Axial load is imparted to the pipe by a screw arrangement and/or by interior oil pressure; and transverse horizontal loading may be applied through a string and pulley. The arrangements for assaying the resistance of the soil to transverse motion of the pipe are described. Results are presented for several tests involving both axial and transverse loading, and cyclic axial loading. The paper concludes with a short discussion.     

Analytical synthesis of mechanisms—Part 2 crank-rotatibility synthesis

The crank-rotatibility synthesis of single degree-of-freedom mechanisms is investigated. This synthesis problem may be defined to be the determination of the allowable dimensions of a mechanism such that a desired link can act as a crank. The developed synthesis algorithm yields, analytically, sufficient conditions for crank-rotatibility. These conditions are in the form of inequalities that involve the dimensions. The method is applicable to any planar or spatial mechanism, for which an appropriate input-output equation may be derived. The algorithm can be used to determine the limit positions of any link in the mechanism.     

An analysis for large deformation of an elastic-plastic bar under repeated axial loading—I: Derivation of basic equations

A brief summary is first made of the hysteretic behaviour, analytical and experimental, of a prismatic bar under variable repeated axial loading, based on earlier studies for small deformation. Basic equations are then derived in a closed form through an elastic-perfectly plastic type of analysis in conformity with one-dimensional idealization, by extending previously obtained principles into the range of large deformation, for determining the load-deformation characteristics of a moderately long bar. Account is taken of changes in geometry due to large transverse deflection and changes in bar dimensions due to plastic elongation.     

Stability analysis of externally-pressurized gas-lubricated porous bearings with journal rotation Part 2. Conical whirl

The stability analysis of externally pressurized gas journal bearings under conical mode of vibration has been obtained using a first-order perturbation method. The effect of journal speed, feeding parameter, supply pressure, porosity parameter and length-to-diameter ratio on the conical whirl and whirl ratio has been investigated.     

Stability analysis of externally-pressurized gas-lubricated porous bearings with journal rotation Part 1. Cylindrical whirl

Whirl stability (cylindrical) of externally-pressurized gas-lubricated porous journal bearings, considering one-dimensional flow through the porous matrix, is analysed by a first-order perturbation method. The effect of supply pressure, feeding parameter, porosity parameter and length-to-diameter ratio on the stability is also investigated.     

The antiwear mechanism of zddp's. Part I

Zinc dialkyldithiophosphates (zddp's) have been used in internal combustion engine oils for over 30 years as antiwear and antioxidant additives. In this paper, their mode of action is investigated. It was concluded, using various analytical techniques, that zddp's decompose in oil solution predominantly by a hydrolytic mechanism, ultimately to zinc polyphosphate and a mixture of alkyl sulphides, which are the precursors of the antiwear action of zddp     

Analytical synthesis of mechanisms—Part 1 transmission angle synthesis

The transmission angle3synthesis of single degree-of-freedom mechanisms is investigated. This synthesis problem can be defined as the determination of the dimensions of a mechanism such that the constraint Δμ < δ is satisfied. Here, Δμ denotes the maximum deviation of the transmission angle, μ, from the optimum one; and δ is a specified bound on Δμ. The developed algorithm yields, analytically, the algebraic conditions (inequalities) that must be satisfied by the dimensions of the mechanism. The method is applicable to any spatial or planar mechanism for which a transmission angle(s) may be defined.     

The antiwear mechanism of zddp's. Part II

The solution breakdown of zddp's to zinc polyphosphates and mixed alkyl sulphides has been discussed. In this paper, their interaction with metal surfaces is pursued using esca. Zinc phosphate is demonstrated to arrive in the surface oxide layer of engine cams and tappets by physical adsorption and FeS is formed via the oxide layer and elemental sulphur generated from alkyl sulphides with Fe₂O₃. It is hypothesized that their presence there as fusible glassy compounds, phosporus as polyphosphate and iron sulphide as a ternary eutectic with iron oxide, provides the antiwear function of zddp