Une autre approche de la formation en simulation mécanique pour la conception

In an industrial context where the simulation of the products behavior has become impossible to circumvent, it rises the question of the knowledge necessary to the realization of these simulations and of the knowledge to be transmitted within the framework of the initial training and the adult continuing education to the simulation of product behavior. The current training dissociates the methods and the fields of application of the simulation of the behavior (in term of physics) in order to apprehend them one by one. This paper deals with the question of the knowledge necessary to the achievement of simulation in a design context and aims at bringing a global and complementary point of view to the classical approach. The first part stresses the importance of the simulation in the design of technical products and presents the problems associated with its teaching. An approach is then presented to cover the entire process of simulation and to structure this process in order to improve the ability to teach it. This approach is based on some research dedicated to the traceability and the capitalization of the knowledge generated by the mechanical simulation of the product behavior. Various experiences concerning the training based on this global solution were carried out and feedback on first experiences are presented and open up some prospects.     

Simulation numérique du confort de sièges d'automobiles : comportement mécanique 3D de mousses de polyuréthanne ; optimisation 2D d'un profil simplifié de siège

Numerical simulation of automotive seat comfort 3D mechanical behaviour of the polyurethane foam; 2D optimisation of a simplified profile of seat. In this article, mechanical behaviour of different polyurethane (PU) foams is investigated. Focus has been placed on the time-dependent behaviour under large deformation. Selected experimental results from uniaxial compressive tests (cycling and relaxation), and simple shear tests are presented. A phenomenological constitutive law is developed and used to model these polymeric foams. Numerical validation of the constitutive model is also described thanks to the simulation of an indentation test. The actual purpose of this study is the simulation of a SAE mannequin sitting in a complete car seat and the optimisation of its geometric form for better comfort.     

Caractérisation expérimentale de paramètres thermomécaniques liés au frottement

Technological progress in infrared thermography has changed the way to study thermal effects in mechanics and, in particular, in contact problems in the presence of friction where a direct measurement is difficult. The method discussed here consists, during wear tests, of estimating simultaneously the evolution of the friction coefficient and the temperature, the latter varying because of the heat generated by friction. The observations are made on a plane, parallel to the plane of contact where the temperature increases because of conduction through the thickness of the specimen. The temperature change is assessed by an infrared thermo-system. This method has great potential especially in the presence of damage in the vicinity of the zone of contact.     

Modélisation de l'effet de la compression d'un renfort de mats de fibres sur la variation de sa perméabilité

Currently, the resin transfer molding (RTM) process is used to manufacture composite parts. This is, in fact, why a great number of researchers devote their attention to the modeling of the RTM process. The determining parameter of the filling simulation by the resin of a mold comprising a fibrous preform is the permeability of the latter. Neverthess, the preforming operation and the closing of the mold lie behind the compression of the preform causing, thus, the variation of its permeability. The aim of the present study is to model the effect of the compression of a fiber mat reinforcement on the variation of its permeability. The problem is treated by studying the compression of the fiber mat reinforcement impregnated with resin according to two approaches: analytically, by assuming that the permeability of the reinforcement remains constant, and experimentally. On the same graph, we plot analytic compression curves for different permeabilities of the reinforcement as well as the experimental curve. The intersecting points of the latter curve with analytic ones allow us to plot the permeability variation of the reinforcement according to its compression rate. An exponential variation law is found out. This latter is used to calculate the effective permeability of the reinforcement at the compressed state.     

啤酒de妙用

啤酒营养丰富,有"液体面包"之称.除作饮品之外,它还有其它许多妙用,现向广大机手朋友介绍如下:     

腕表de运动主义

运动表的品质 2006年巴塞尔展览会和SIHH展上推出的运动型手表不仅体现了现在的流行趋势:品质要求更高,用途更广泛,更重要的是不论是在运动场,还是办公室和餐馆,佩戴都十分协调.尽管目前在选择运动表材料时主要使用的还是黑色塑胶,但外形的设计却更加符合现代审美观,功能也越来越全面.     

Prototypage virtuel : exemple de crash de véhicules ferroviaires

Virtual prototyping: the case of rolling stock crashworthiness. Virtual prototyping is the result of the extraordinary development of the capabilities of numerical simulation techniques. Its objectives are to progressively replace actual prototypes, costly in time-delays and prices, by numerical models. Design of crashworthy vehicles is one of the potential applications of this new procedure. The railstock industry, which was far behind automotive industry in this field, is now developing more and more efficient models. The crashworthy design methodology developped by the LAMIH uses two prototypes: the first one takes place in the first stage of design and is a mock-up using indirect similarity, the second one is the final prototype. The objective of this paper is to acknowledge new possibilities and persisting difficulties in applying virtual prototyping to crashworthy design of rail-stock vehicles.     

蜗轮滚刀de设计

1.蝸輪滚刀的分类: (1)按滚刀的螺旋面形式分为阿基米德螺旋面和法向直廓螺旋面两种,螺旋面为阿基米德的蜗轮滚刀齿形在轴向剖面内为直线,所以它的制造简单,测量方便是目前应     

Principes variationnels et exploitation de mesures de champs en élasticité

Sometimes parameters pertaining to constitutive materials or to the overall definition of a mechanical structure need to be identified in an indirect manner from experimental measurements. Field measurements provide rich data and, as such, are particularly well suited to material or structural parameter identification problems. In this article, identification techniques specifically devised for the exploitation of field measurements are presented. The identification of distributed elastic moduli is used as a model problem, but other identification problems can be treated along similar lines. This article emphasizes the fact that one is by no means limited to using output least-squares cost functions for solving such identification problems. Indeed, the availability of field measurements allow to define other criteria, well-suited to this type of data and directly linked to fundamental variational principles. Most of this article is devoted to two criteria of this family, namely the error in constitutive equation and the reciprocity gap functional. Various illustrative examples, generally of a synthetic (i.e., purely numerical) nature are provided.     

工程机械的"补"与"不补"

工程机械是否应当进入＂农机补贴目录＂,一直是一个让人避讳莫深、难以回答的问题。近年来,各省农机补贴目录越来越多地出现了工程机械的身影,而且这些产品也已经不再仅仅是简易的农用工程机械。2011年,在国家的补贴目录中,也出现了斗容量≤0.4m~3的挖掘机的选项。     

Modélisation des frottements dans les éléments de transmission d'un axe de robot en vue de son identification

Control in robotics needs more and more precise models of the mechanical parts of the structure and specially for a complex system such as a biped robot. An important but difficult aspect of this work is the modelling of the mechanical loss due to friction in the chain of transmission from the motor to the axis. The loss of each part is defined as a sum of three terms, one constant, another depending only on the speed and the last depending on the torque transmitted in the part. The robot joint kinematic chain is modelled with three elements: the motor, the gearbox and a rotational joint at the leg. The results show a good adequacy between the measurement and the simulation with the proposed identification method in comparison with a classic least square identification method.     

Is “five-point” estimation better than “three-point” estimation?

Theoretical considerations are presented to show that, regarding [1], for a sinusoidal signal, “five-point” estimation is a better estimation than “three-point” estimation.     

<机械制造业产品与市场预测>出版

本刊讯为促使我国制造业特别是机械制造业广大企业能及时、全面了解本行业产品、技术的发展趋势及市场需求状况,机械科学研究院组织各方力量,对我国机械制造业18个产业产品与技术发展趋势进行了预测. 预测的主要内容包括: 1.各产业产品发展趋势和发展重点; 2.对重点发展产品的市场需求、发展方向、主要指标和技术特点、技术关键、实用化时间等进行分析和预测; 3.各产业需要解决的关键技术,并对每项关键技术进行论证.包括:技术概要、选择的依据、国内外现状与发展趋势、主要研究内容和目标. 18个产业分析与预测小组,经过充分分析论证,并咨询了数百名专家的意见,现已完成了课题研究工作.其成果已汇集成册,总计70万字.研究报告内容丰富、信息量大,具有权威性,可为制定这些行业的“十五”发展规划、计划提供依据,对制定企业发展战略和规划有导向作用.为满足各单位急需,现将其中的工程机械、农业机械、内燃机、冶金矿山机械、通用设备、石油机械、环境保护机械、发电及输变电设备、金属加工机械(机床)、通用仪器仪表、汽车、通用零部件、船舶、轻工机械、纺织机械等15个产业的预测结果做为资料予以发行. 价格:合订本每套300元,含邮寄费. 征订办法:通过邮局汇款.请将收件人姓名、详细地址、所在单位及部门、邮政编码用楷书写清,并在汇款单的留言中注明所需资料名称、数量.收款后即将资料和正式发票以挂号方式从邮局寄出, 联系人:王勇、郭壮电话:(010)68596023、68527633 详细地址:北京市月坛南街26号中国机电日报社邮政编码 100825 　　……     

Tribological Properties of Organic Functionalized ZrB<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Epoxy Composites

The tribological behaviors of epoxy composites filled with organic functionalized ZrB₂–Al₂O₃ were environmentally investigated and compared with those with as-received fillers under both dry and oil sliding conditions in this work. The worn surfaces and the transfer films on the counterparts were characterized by scanning electronic microscope (SEM), and the frictional temperature rising was investigated by infrared thermometer. The results demonstrated that the coefficient of friction (CoF), the wear rate, as well as the frictional temperature rise of the epoxy composites were all decreased due to the introduction of ZrB₂–Al₂O₃ fillers. And with the increase in filler content, similar variation tendencies of CoF and wear rate of epoxy composites were observed under the different sliding conditions. Besides, the organic functionalization of ZrB₂–Al₂O₃ fillers, which made the epoxy composites exhibit lower CoF and wear rate than those with as-received fillers, lowered the frictional temperature as well. In comparison, the epoxy composites filled with 5 vol% modified fillers presented better tribological properties, suggesting a stronger interfacial bonding between modified fillers and epoxy matrix. The dominant wear mechanisms of filled composites under dry and oil sliding conditions could be inferred as the combination of adhesive wear and abrasive wear and the fatigue wear, respectively, on the basis of SEM images of worn surfaces.     

In Situ Studies of TiC<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Hard Coating Tribology

TiC_1−x N _x hard coatings present time-dependent tribological behavior with an initial running-in period (500–2000 cycles) marked by an elevated friction coefficient, followed by >10000 cycles with low-friction and wear at room temperature (RT) in ambient air. The mechanisms behind this behavior are not completely understood. Tribological tests performed at RT and at different relative humidity (RH) levels revealed that a minimum value between 15 and 25% RH is needed to trigger the low-friction regime at a sliding speed of 100 mm s⁻¹. By in situ observations of transfer film growth, it could be observed that third body material is formed during this running-in period by plowing of the coating and shearing of the removed material. The appearance and thickening of the transfer film marks the beginning of the steady-state low-friction regime where the velocity is accommodated by interfacial sliding. At this stage in the tribological test, the recorded Raman spectra indicated the presence of C–H bonds in the wear track. Use of in situ analytical tools during wear tests provided insights with respect to tribological phenomena that were not available by conventional, post-mortem analysis methods.     

Dynamics of Growth of the Native Oxide of Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te

The growth of the native oxide of the Cd_xHg_1?xTe (MCT) compound is studied by methods of laser and spectral ellipsometry. It is found that a non-absorbing oxide film is formed from the very beginning in the case of MCT oxidation with hydrogen peroxide vapors, whereas oxidation with atmospheric oxygen leads to the formation of absorbing layers on the surface at the first stages of the process. When the oxide film thickness reaches 1–2 nm, the oxidation rate drastically decreases. If MCT samples that were stored for a long time (for years) in air at room temperature are heated at T = 200 °C, the optical thickness of the oxide film decreases.     

A comparative evaluation of K<Subscript>op</Subscript> determination and ΔK<Subscript>eff</Subscript> estimation methods

Methods for determination of the crack opening stress intensity factor (K_op) and for estimation of the effective stress intensity factor range (ΔK_eff) are evaluated for crack growth test data of aluminum alloys. Three methods of determining K_op, visual measurement, ASTM offset compliance method, and the neural network method proposed by Kang and Song, and three methods of estimating ΔK_eff, conventional, the 2/P10 and 2/PI methods proposed by Donald and Paris, are compared in a quantitative manner by using evaluation criteria. For all K_op determination methods discussed, the 2/PI method of estimating ΔK_eff provides good results. The neural network method of determining K_op provides good correlation of crack growth data. It is recommended to use 2/PI estimation with the neural K_op determination method. The ASTM offset method used in conjunction with 2/PI estimation shows a possibility of successful application. It is desired to improve the ASTM method.     

Environmental Effects on the Tribology and Microstructure of MoS<Subscript>2</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>–C Films

The tribology of molybdenum disulfide (MoS₂)–Sb₂O₃–C films was tested under a variety of environmental conditions (ambient 50% RH, 10⁻⁷ Torr vacuum, 150 Torr oxygen, and 8 Torr water) and correlated with the composition of the surface composition expressed while sliding. High friction and low friction modes of behavior were detected. The lowest coefficient of friction, 0.06, was achieved under vacuum, while sliding in 8 Torr water and ambient conditions both yielded the highest value of 0.15. Water vapor was determined to be the environmental species responsible for high friction performance. XPS evaluations revealed a preferential expression of MoS₂ at the surface of wear tracks produced under vacuum and an increase in Sb₂O₃ concentration in wear tracks produced in ambient air (50% RH). In addition, wear tracks produced by sliding in vacuum exhibited the lowest surface roughness as compared to those produced in other environments, consistent with the picture of low friction originating from well-ordered MoS₂ layers produced through sliding in vacuum.