Stability analysis of four bar mechanism. Part II— taking damping into consideration

In[1], a technique is developed to study the stability of the mechanism having elastic links, where damping is not taken into consideration. Here we develop a technique to study the stability of the practical four bar mechanism, taking damping into consideration. The system behaviour is studied at various speeds in different regions. Also the comparison of damped and undamped displacement responses is presented.     

Deformation processing of metal powders: Part I—Cold isostatic pressing

Analytical and numerical techniques are used to analyze in detail the stage I Cold Isostatic Pressing (CIPing) of metal powders. Plastic yielding is considered to be the only densification mechanism and the constitutive model developed recently by Fleck, Kuhn and McMeeking [(J. Mech. Phys. Solids40, 1139 (1992)] is used to describe the elastoplastic behavior of the metal powder. It is shown that, for the case of powder consolidation in a long cylindrical tube, a change in length is not possible, unless it is accompanied by some distortion (“shape change”) of the CIPed specimen. The numerical implementation of the constitutive elastoplastic equations in a finite element program is discussed. The finite element method is used to analyze the CIPing of titanium powder. The predictions of the finite element solution agree well with available experimental data.     

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.     

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。     

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.     

Coating thickness effects on initial wear of nitrogen-doped amorphous carbon in nano-scale sliding contact: Part I—in situ examination

This paper, the first of a two-part series, presents the empirical data obtained from in situ examination on the generation of wear particles on carbon nitride coatings by a spherical diamond counter-face during repeated sliding contacts. In particular, the effect of coating thickness, varying from 1 to 500 nm, on the generation of wear particles was examined.Based on the in situ examination, the shape transition maps for generated wear particles were obtained for carbon nitride coatings of various thickness. The results show that the critical number of friction cycles, Nc, for the transition from “no observable wear particles” to “wear particle generation” generally increased with increasing coating thickness. It was noted that up to 20 friction cycles, the maximum Hertzian contact pressure, P_max, for “no observable wear particles” regime can be increased from 1.39Y to 1.53Y if silicon was coated with carbon nitride coating thicker than 10 nm, where Y is defined as the yield strength of silicon.     

Long rod penetration models—Part II. Extensions to the hydrodynamic theory of penetration

The modified hydrodynamic theory of penetration is extended to take account of the transient, plastic-wave dominated and after-flow phases of penetration. It is also indicated how a more detailed flow field model of the primary phase of penetration leads to the modified Bernoulli equation and a relationship between the dynamic yield strength and the strength factors R_t and Y_p. The effect of the decelerative motion on the modified Bernoulli equation is also briefly examined. Finally, the theory is compared with experimental results of previous papers.     

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.     

金属橡胶阻尼元件减振性能的试验研究

对金属橡胶阻尼元件的减振性能进行了试验研究,并进行了机理分析。     

金属橡胶阴尼元件减振性能的试验研究

对金属橡胶阻尼元件的减振性能进行了试验研究,并进行了机理分析。     

Machining with tool–chip contact on the tool secondary rake face—Part II: analysis and discussion

The forces, chip thickness, and natural tool–chip contact length in machining with a double-rake-angled tool are predicted in Part II of the present study. It is revealed that in comparison with a single-rake-angled tool, a double-rake-angled tool increases the forces, especially the thrust force. However, the increase in chip thickness and tool–chip contact length is not significant under the input conditions specified in the present study. The effect of seven input variables of the proposed model is quantitatively investigated. The predicted variations of forces, chip thickness, and natural tool–chip contact length are in good agreement with theoretical and experimental results obtained by other researchers. The interrelationships among the resultant force, the chip thickness, and the natural tool–chip contact length are established, which provides a new and promising method to estimate the tool–chip contact length by employing the resultant force. It is demonstrated that the model can also be extended to study the problem of machining with a groove-type chip breaker tool.     

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 complex buckling of flexible sheet materials—Part II. Experimental study of three-fold buckling

This paper reviews the technological importance of the problems of complex buckling of textile fabrics and other sheet materials and the reasons why conventional shell theory is of little value. It stresses the importance of the occurrence of membrane strains in double curvature over finite areas, reviews earlier work on the subject, discusses briefly the characterization of the properties of sheet materials and shows the approach to the problem through simple three-fold buckling. A major section of the paper relates to order-of-magnitude estimates of bending, membrane and gravitational energies and introduces two important dimensionless groups, J₁ = Yl²/D and J₂ = γgl³/D, in terms of which deformed shapes can be calculated. A mathematical model for three-fold buckling is described and the contributions of different energies during deformations are presented.     

A new method to simulate the elastic interactions in the tribosystems of a multi‐bar mechanism

This paper presents a new method and criterion for predicting the occurrence of the interruption of a kinematic joint contact in a multi‐bar mechanism. The method is based on the elastic interactions in the tribosystems of the joints with imposed clearances. The method was used in a four‐bar mechanism with clearance in the joint formed from the coupler and the rocker. The analytical results were experimentally confirmed by measurement of the acceleration of the rocker.     

Thermo-hydrodynamic analysis of the finite slider pad—Adiabatic conditions

Results are presented of a three-dimensional analysis of the fluid film under a square fixed-geometry inclined slider pad. The analysis is applied to adiabatic conditions as a first step in the investigation of transverse viscosity gradient effects for a wide range of operating conditions. The predicted performance is compared with that obtained on the assumption of viscosity constant through the film thickness. The effect of the transverse viscosity variation is shown to reduce or enhance pressure generation according to the magnitude of two characteristic non-dimensional groups. The results are also compared with performance predicted on the basis of constant viscosity theory using an “effective” viscosity derived from an overall film energy balance.     

The weight vector theory of Coriolis mass flowmeters — Part 2. Boundary source of secondary vibration

The purpose of this short paper is to draw attention to a boundary source of secondary vibration in Coriolis mass flowmeters. This is important in the calculation of meter sensitivity using the weight vector theory if the effect of fluid viscosity is to be taken into account in the vibrational flow.     

汽车零部件出口形势有望下半年回转

随着金融危机的蔓延,汽车出口结束了2008上半年的高增长状态,在第三季度进入了下滑通道,而2009年以来的形势更加不乐观,延续下滑趋势,下降幅度高达二成以上。     

The myofibrillar M-band in the cryo-section—analysis of section thickness

Information regarding the formation and the thickness of cryo-sections is of importance for an adequate interpretation of cryo-sectioned biological material. In this study we have taken advantage of the regular arrangement of filaments in myofibrils in an analysis of these matters. It is concluded that the sections are formed partly by fracturing in a way similar to that visualized in replicas made by the freeze-fracturing and -etching procedure.     

Authentication of Chinese Materia Medica decoction dregs. Part II: comparison before and after decoction of four Chinese Materia Medica that mainly comprise storage tissue

Authentication of Chinese Materia Medica (CMM) decoction dregs is important for ensuring the efficacy and safety of CMM when they are used in decoction. If someone got worse or poisoned after taking a decoction while the formula is appropriate, the authentication of CMM dregs is the effective method to explore the reasons. Therefore, a systematic study on the authentication of CMM dregs was carried out. In this study, two pairs of easily confused CMM dregs, Fenge (Puerariae Thomsonii Radix) and Shanyao (Dioscoreae Rhizoma), Dihuang (Rehmanniae Radix) and Huangjing (Polygonati Rhizoma), which mostly comprise storage tissues, were investigated by comparing the morphological and microscopic characteristics. Fenge and Shanyao contain abundant starch granules. After decoction their dregs were hard, nonstarchy and horn-like. Fully gelatinized starch granules were found in the powder of Fenge dregs while incompletely gelatinized starch granules were occasionally found in the Shanyao dregs. In contrast, Dihuang and Huangjing contain water-soluble sugars. After decoction, their dregs were hard and brittle. Their parenchymatous cells were shrunken and unknown crystals were found under microscope. Hence, the morphological and microscopic characteristics of CMM before and after decoction were different, and different changes in the CMM dregs can be illustrated by the different nature of their ergastic substance. These differences could be used to authenticate CMM dregs.