Experimental study of wear of model friction pairs lubricated with contaminated oil

The results of tribotests of block-on-ring friction pairs, which are analogs of piston–liner friction pairs of axial-piston pumps, are presented. It has been shown that, when the pairs are lubricated with oil that contains inorganic contaminants, the wear rate of the steel specimen is more than 200 times higher than that of the bronze specimen. It has been found that the concentration of contaminants in oil of 0.02–0.03% is permissible for block-on-ring friction pairs. The dependence of the wear rate of the specimens on the concentration of the solid contaminations is described by a logarithmic function, while the dependences of the coefficient of friction and the contact temperature on this concentration are described by hyperbolic functions. This has made it possible to assume that the wear of the specimens is determined by the hydroerosion component, which enhances the abrasive effect of the solid contaminations.     

Selecting Optimum Parameters of Ultrasonic Noncontact Shadow Method for Testing Products Made of Polymer Composite Materials

Russian Journal of Nondestructive Testing - It has been shown that in order to increase the sensitivity of ultrasonic noncontact shadow testing of products made of polymer composite materials...     

Contact and wear of paper-based friction materials for oil-immersed clutches—wear model for composite materials

Paper-based friction materials are widely used for oil-immersed clutches in automatic transmissions for passenger cars. It is known that repetition of engagements of the clutches causes wear of the friction materials leading to running-in with an increase in contact area. Observation of the contact of a typical paper-based friction material has been made by contact microscopy using the reflection of polarized light. The results have shown that contact is made at the top of its particulate and fibrous constituents, and comparison with the results of laser microscopy has revealed that the contact area observed by the contact microscopy is the contour contact area. An analysis has been made to describe this behavior by employing a mechanical model in which spherical and columnar asperities are supported by an elastic halfspace and wear under the loads they support. Analytical results describe the observed change in the contour contact area and demonstrate applicability of the model to wear of composite materials.     

Effect of deformation martensite on the electrical and magnetic properties of plastically deformed chromium–nickel steel

Connection between the structural and phase changes in specimens of chromium–nickel austenitic steel and their magnetic and electrical properties has been studied. It has been established that electric resistivity can be used as an additional testing parameter for the phase composition of plastically deformed articles made of austenitic-ferritic steel. It has been shown that the emergence of an additional phase of strain-induced martensite leads to a significant increase in electric resistivity.     

Methods of increase of structural strength of spherical pressurized containers

Ways of increasing the structural strength of spherical pressurized containers made of titanium alloy are described. The author suggests using the technological scheme of pressure welding/superplastic forming for production of full-strength containers. It has been shown that the principle of multilayer and ultra-fine-grain rolled sheet can be used for increase of structural strength.     

Quantitation in biological X-ray microanalysis, with particular reference to histochemistry.

Thin specimens consisting of various light and heavy elements in gelatine have been subjected to X-ray microanalysis to determine the relationship between the number of X-ray counts for a specific element expressed as a percentage of the continuum (the percentage counts) and the concentration of that element. For light elements, the relationship between the percentage counts and concentration is strictly linear. For heavier elements, the relationship is not linear, because of the increase of the continuum counts with (formula: see text). If a correction is made for the effect of (formula:see text), heavy elements also show a linear relationship between percentage counts and concentration. Within the limits of atomic number (Z = 56) and concentration (approximately 10%) studied here, it is shown that when X-ray microanalysis is carried out on bulk specimens consisting of various elements in gelatine, the relationship between X-ray counts and concentration for a particular element is linear. The problems in quantitation of the results of X-ray microanalysis caused by exogenous continuum and mass loss induced by irradiation are discussed. It is pointed out that when X-ray microanalysis is used to study histochemical and other staining procedures, allowance must also be made for the reduction in concentration of other elements in the specimen as a result of the addition of the stain to the specimen.     

A CFD model of particle concentration effects on erosion–corrosion of Fe in aqueous conditions

A CFD (computational fluid dynamics) model has been developed to evaluate the effects of particle concentration on the erosion–corrosion of the inner surfaces of a circular pipe of 90° bend at room temperatures. The relative intensity of erosion and corrosion around the pipe geometry results in transitions between various erosion–corrosion regimes, for a given inlet particle concentration. The results indicate that the corrosion-dominated regime at the pipe bend is reduced with an increase in particle concentration. Typical results from the model are shown illustrating how this 3D mapping method can be used to model parameters such as particle concentration on the erosion–corrosion regimes over the surface.     

Antispalling Effect of WS2 Nanoparticles on the Lubrication of Automotive Gearboxes

The effect of WS₂ nanoparticles used as lubricant additives in the lubrication of automotive gearboxes has been studied. The results suggest that nanoparticles can be used to increase the life span of the mechanical parts of gears. Chemical analyses and observations made after transmission tests have shown that nanoparticles are able to go inside cracks and may have a sealing effect, preventing spalling and further failure of the material. Moreover, the addition of nanoparticles in fully formulated oil reinforces the antispalling properties of the lubricant.     

A model for the lubrication mechanism in knee joint replacements

Analytical studies are presented of the lubrication mechanism occurring in knee-joint replacements under restricted motion. The idealized model is shown to produce results consistent with those in normal situations. The effects of increasing the viscoelastic parameter of the lubricant are similar to those produced by an increase in the concentration of hyaluronic acid molecules in synovial fluid. Slip velocity occurring at the porous boundary aids the normal functioning of the joints. The load capacity of the replaced tibia has been shown to increase as the gap closes and/or the femoro-tibial angle decreases from π/20 to ?π/20 rad.     

Effect of Copper Content on Tribological Characteristics of Fe−C−Cu Composites

The paper presents the results of an investigation of the effect of the copper content on the tribological characteristics of Fe?C?Cu composites. It has been shown that the best tribological properties and hardness are shown by material containing 3% copper. In the case of a 10% copper concentration, the wear rate of the composite rises by as much as ten times, while at a 20% concentration, it decreases. It has been proved that the copper concentration significantly affects the formation of friction surface morphology.     

The effect of the structural features of polytetrafluoroethylene-based composites on the reduction of matrix loading

It has been shown analytically that a decrease in the matrix loading due to a finely dispersed filler in a material that has a distribution like a segregated network is one of the reasons for an increase in the tribological properties of polytetrafluoroethylene-based composites. The relationship between the matrix loading of the composite and the concentration and size of the filler particles is revealed. An example of how to calculate the matrix loading of a polytetrafluoroethylene-based composite with a diamond powder filler with a mean particle size of 50 nm is given.     

The discharge from a thin slot over a surface of convex curvature

An investigation has been made into the discharge from a thin slot over a surface of convex curvature. It was found that for unchoked flow, the discharge coefficient is increased over that for discharge over a flat surface. The increase is due to the subambient pressures on the surface and a theory has been developed which will satisfactorily predict the increase and the surface pressure. For choked flow the convex surface has no effect on the discharge coefficient.A brief investigation has also been made of the conditions for separation of the jet from the surface. Bistable regions were found at both low and high blowing pressures, but the details are likely to be very dependent on slot geometry.     

CCD微阵列生物芯片扫描仪的研制

报导了CCD微阵列生物芯片扫描仪的光学系统 ,给出了光学系统的参考标准构型 ,并依据此构型研制出多分辨率CCD生物芯片扫描仪。实验采用不同浓度系列Cy3NHSester的DMS0溶液样点与微池溶液测定CCD生物芯片扫描仪的检测性能。初步实验数据表明 ,此扫描仪光路合理 ,精度满足生物芯片检测要求。     

近三十年来我国有关美国教师问题的研究状况——基于“中国知网”相关文献的分析

立足于“中国知网”，对1980～2009三十年来该数据库收录的有关美国教师问题的学术文献进行了统计分析。从论文发表数量的年代分布、论文选题的主题分布、论文发文量居前8位的作者分布、论文发文量居前18位的单位分布、论文发文量居前10位的期刊分布五个方面，探讨了近三十年来我国有关美国教师问题的研究状况。以具体的统计数据揭示了我国有关美国教师问题研究的若干特征：研究范围不断扩大，研究主题不断增多，研究内容不断深化；研究者主体队伍既相对稳定又有新兴力量的崛起。同时指出，我国在有关这一领域的若干基础问题与热点问题的研究还相对薄弱，研究群体主要局限于高校学者，主张倡导和鼓励与我国基础教育关系更为密切的各地教育学院和各地教科院、所等机构参与这一领域的研究，研究的领域范围尤其是对学前教育的研究还应进一步拓展。     

Ultrasonic control of welded joints in a Du800-type pipeline. Part II: Improving image quality and comparison with X-ray testing results

It has been shown in the first part of the article that the DFA method in its version intended for ultrasound propagating in a homogeneous isotropic medium does not suffice for reconstructing high-quality images of reflectors in the welded joint of a Du800-type pipeline. To improve the image quality further while using the DFA method, it is necessary to determine the elastic properties of a Du800 pipeline buildup and allow for its anisotropy with respect to the propagation of ultrasound as well as the surface profile. The DFA-Y and maximum-entropy (ME) methods have been applied to increase the resolving ability and reduce the noise level. Comparing the results of ultrasonic and X-ray testing has made it possible to draw a conclusion that the former is more informative for revealing crack-like reflectors.     

Creep modeling in functionally graded rotating disc of variable thickness

Creep behavior of rotating discs made of functionally graded materials with linearly varying thickness has been investigated. The discs under investigation are made of composite containing silicon carbide particles in a matrix of pure aluminum. The creep behavior of the composite has been described by threshold stress based creep law by assuming a stress exponent of 5. The effect of imposing linear particle gradient on the distribution of stresses and strain rates in the composite disc has been investigated. The study indicates that with increase in particle gradient in the disc, the radial stress increases throughout the disc, whereas the tangential and effective stresses increase near the inner radius but decrease near the outer radius. The steady state strain rates in the composite disc, having gradient in the distribution of reinforcement, are significantly lower than that observed in a disc having uniform distribution of reinforcement.     

Analysis of heavy duty tilting-pad journal bearing taking into account pad distortion and possible adoption of rubber pad segments

In this work a comparative study has been made between the thermo-hydrodynamic performance of a three shoe tilting-pad journal bearing with rigid and elastic pads subjected to unbalance load. A case study of a bearing adopting three rubber pad segments has also been studied. The distortion of the elastic pad is introduced into the distribution of the film thickness through an iterative scheme to assess its effect on the load carrying capacity of the bearing. A finite element mesh is used to calculate the distortion of the elastic pad while a finite difference mesh is used to calculate the pressure field in the lubricant film. Results have shown a number of interesting conclusions regarding the adoption of rubber pad segments instead of tilting-pads. There is an increase in minimum oil film thickness when using elastic pad or even rubber pad segments compared with rigid pads. Also the maximum pressure and load carrying capacity are not significantly affected.     

Friction and wear of polyamide-6 powder coatings gradient-filled by metal nanofilms

The tribological properties of PA-6 and PA-6-based coatings with surface layers gradient-filled with tin, lead, and bismuth nanofilms in a concentration of up to 1.2 wt % are compared. It has been found that differences in the tribological behavior of the composites are due to the adhesion of the filler metals to the counterbody material. It has been shown that the hardness of the friction surface of the composites depends on the susceptibility of the filler metals to strain hardening and explains differences in the values of their wear.     

Application of TOC embedded ILP for increasing throughput of production lines

Under fairly special circumstances, there are some special methods that can be used to attempt to increase the production rate of some production line systems. In this paper an attempt has been made to use the theory of constraint (TOC) approach to identify the critical machines. Various design alternatives are considered to increase throughput of the critical machine. This process is continued till the required throughput is achieved for the entire system. For large production line systems this approach will be tedious and time consuming. Hence we have attempted to generalize the TOC approach by integer linear programming (ILP) to increase the throughput. Data has been collected from an automobile ancillary manufacturing industry to validate the model. The TOC embedded ILP has been used to increase the throughput with minimum investment.     

A large-area streak tube with magnetic focusing and fast image scan

Certain problems encountered in the development of a large-area streak tube (ST) with magnetic focusing and fast image scan are considered. It is shown that the use of a spherical accelerating electrode made of fine-structure mesh makes it possible to considerably increase the ST working area. The designs of the large-area ST are described, and its estimated characteristics are presented. The large-area ST based on these calculations has found practical use in a streak camera designed to operate with a resolution of the order of 2 ps in the soft X-ray region.