Ensuring Lateral Clearance in Gears by Displacing the Initial Tool Contour

Russian Engineering Research - Multicriterial optimization of gear engagement by means of Kompas-3D software permits calculation of the tool displacement required to ensure lateral clearance in...     

The fracture resistance and crack-tip micromechanics of in-situ intermetallic composites

The Cr₂Nb intermetallic compound is attractive as a high-temperature material because of its high melting point, low creep rate, and good oxidation resistance. However, this material is also extremely brittle at ambient temperature. Consequently, substantial efforts have been made to develop Cr₂Nb-based in-situ composites containing a ductile phase with the aim of imparting fracture resistance while maintaining most of the high-temperature properties. This article presents an overview of the effects of matrix composition on the fracture resistance and crack-tip micromechanics for Cr₂Nb-containing in-situ composites based on the Nb-Cr-Ti system. Crack-tip strain measurements are presented to illustrate the important effects of titanium addition on the ductility of the solid-solution phase and the fracture process in the in-situ composites.     

Uncertainty analysis of nonlinear systems employing the first-order reliability method

In most mechanical systems, properties of the system elements have uncertainties due to several reasons. For example, mass, stiffness coefficient of a spring, damping coefficient of a damper or friction coefficients have uncertain characteristics. The uncertain characteristics of the elements have a direct effect on the system performance uncertainty. It is very important to estimate the performance uncertainty since the performance uncertainty is directly related to manufacturing yield and consumer satisfaction. Due to this reason, the performance uncertainty should be estimated accurately and considered in the system design. In this paper, performance measures are defined for nonlinear vibration systems and the performance measure uncertainties are estimated employing the first order reliability method (FORM). It was found that the FORM could provide good results in spite of the system nonlinear characteristics. Comparing to the results obtained by Monte Carlo Simulation (MCS), the accuracy of the uncertainty analysis results obtained by the FORM is validated.     

Finite-element analysis for magnetic resonance image artifact evaluation

The static magnetic field of a magnetic resonance imaging scanner can be distorted by the presence of materials, perturbing the spatial encoding process in magnetic resonance imaging and often resulting in image artifacts. The relationship between the image artifact size and magnetic susceptibility of the material specimen is of interest to engineers for the design of devices that are to be compatible with the imaging volume of the scanner. In this study, a finite-element method was used to simulate the distorted magnetic field of samples with different susceptibilities. With the knowledge of the external- and self- magnetic field interactions, a Lorentz correction was applied to compute the magnetic field deviation. The simulated results were then validated by the corresponding experimental magnetic resonance images.     

Studies of the interactive effect of specimen and grain sizes on the plastic deformation behavior in microforming

Microforming process provides an efficient approach to fabricating microparts via microscaled plastic deformation. However, the material properties change and the size effect occur when the workpiece size is scaled down from macro- to microlevel, which makes the development of microforming system difficult. It is thus necessary to study the size effect phenomena and microscaled deformation behaviors. In this research, the upsetting of annealed pure copper cylinders with different sizes from macro- to microscale is conducted to investigate the interactive effect of specimen and grain sizes on material deformation behavior. It is found that flow stress decreases and surface roughening and inhomogeneous flow take place with the increase of grain size and the decrease of specimen size. Furthermore, the properties of grain interior and grain boundary change, and the properties of surface grains become significant in the overall deformation behavior. It leads to the deviation between the Hall–Petch relation and the experimental results. It is further revealed that the flow stress has a linear relationship with the ratio of specimen size to grain size (D/d) at a given strain, and the change rate of the flow stress with D/d could be independent of strain. By examining the changes of working hardening and slip distance, it is found that there could be a delay in the formation of dislocation cell, and the slip distance and the size of dislocation cell could increase with the decrease of D/d. The presented size effect phenomena and the discussed physics thus provide a basis for the further exploration of the microscale plastic deformation behavior.     

等几何分析中Dirichlet边界条件的配点施加方法

相对于传统有限元,等几何分析使用NURBS基函数统一表示几何和分析模型,它能消除传统有限元的网格离散误差,容易构造高阶协调单元。但是由于NURBS基函数缺乏插值性,控制顶点也不一定位于几何边界上,使得难以直接施加Dirichlet边界条件。针对这一问题,提出一种基于样条拟合的Dirichlet边界条件施加方法,通过引入一组边界配点来拟合边界条件。注意到不合适的配点策略会使得边界插值方程组奇异或者条件数过大,详细讨论配点选取的基本准则,提出两种鲁棒的配点方案:Greville横标和Chebyshev插值点法。并且将配点方法扩展到最小二乘形式,设计一种快速的场变量消去算法。通过实例验证上述方法的可行性和有效性。试验结果表明,各种配点策略的收敛率基本保持在一个量级,因此配点法的关键是选择稳定的配点方案。     

可磨硬齿面蜗轮与蜗杆的共轭

本人提出了一种新的共轭啮合齿面成形方法及其在钢制蜗轮蜗杆中的应用 ,理论上和实践上均有重大意义。     

<Emphasis Type="Bold">A Web-Based Product Modelling Tool – A Preliminary Development</Emphasis>

This paper presents the preliminary development of a Web-based Product Modelling Tool (WPMT) aimed at enabling collaborative design through the Internet using JAVA 3D with dispersed team members. It is motivated by the emerging need of distant collaborative design required among R&D centres and manufacturers of global-based enterprises, simply to shorten product cycle time and, hence, to enhance their world-wide competitiveness. In this paper, current web 3D technologies are discussed first, then the general architecture of the underlying WPMT is introduced. The proposed WPMT is developed to allow designers/users to create, view, and manipulate product models through the World Wide Web. The main architecture of the proposed WPMT uses a Java servlet embedded in an HTML web page, which can be viewed and edited by authorised users with a Java/Java 3D enabled browser through the Internet. The developed WPMT is to be run on a Java Virtual Machine (JVM), so it is independent of the operation system and computer platform. Since the WPMT is a web-based modelling tool, some handy built-in primary features such as block, wedge, rim, hole, pocket, etc. are included for users to develop their product models. The users can also create their own features as so-called user-defined features. In addition, viewing operations such as rotation, zooming, panning, orthographic projections and so on, are also made available for comprehensiveness in the integrated web-based solid modelling tool. Finally, the proposed WPMT is experimentally implemented.     

Differential expression of S100 proteins in the developing human hippocampus and temporal cortex

S100 calcium binding proteins have long been known to express in the adult nervous system, but their distribution in the developing brain, especially the human fetal brain, is largely unknown. We used an immunohistochemical method to determine the expression of three S100 proteins, namely S100A4, S100A5, and S100A13, in the human fetal hippocampus and temporal cortex from 12 to 33 weeks of gestation. At 12 weeks, S100A5 was strongly expressed in the cells and fibers of the polymorphic, pyramidal, and molecular layers of the hippocampus. Thereafter, its expression decreased with age. In the temporal cortex, S100A5 expression was detected from 12 weeks onwards, peaked at 20 to 24 weeks, and then decreased with age. The horizontal fibers of the marginal zone were immunoreactive at all stages examined. S100A13 immunoreactivity was also detected in both cells and fibers of the hippocampus at 12 weeks, became slightly stronger at 20 weeks, and then decreased with age. In the temporal cortex, S100A13 immunoreactivity was also strong in all cellular layers at 12 to 24 weeks before it declined with age from 28 weeks onwards. Among the three proteins examined, S100A4 showed the weakest expression, which was detected in the cells and fibers of the hippocampus and the temporal cortex at all stages examined. Our results have demonstrated for the first time, in the human fetal hippocampus and temporal cortex, specific spatio-temporal patterns of expression of these proteins, all of which are likely to have different roles to play during development despite their pronounced sequence homology.     

Rapid manufacturing techniques in the development of an axial blood pump impeller

This paper presents a comparison of manufacturing techniques used in the development of an axial blood pump impeller. In this development process the impeller was designed and its performance was evaluated with the aid of computational fluid dynamics (CFD). Prototypes of those designs where the CFD results show promise were needed in sufficient quantities at a low cost for experimental validation of the CFD results. As the impeller is less than 16 mm in diameter with a maximum blade thickness of about 1.5 mm, innovative manufacturing techniques are explored in this paper to determine the best process for quick fabrication of prototypes that are dimensionally accurate, structurally robust and low in cost. Four rapid prototyping techniques were explored. The completed parts were compared on the basis of manufacturing time, quality and strength of parts obtained, manufacturing cost and also in vitro performances. Based on these studies, it was concluded that selective laser sintering (SLS) is the most appropriate method for the quick production of prototype parts for evaluation of pump performance.