A novel sensor using photo-interrupter for measuring static friction coefficient

A force sensor design utilizing a photo-interrupter is presented for measuring the static coefficient of friction (COF). The measurement of ice friction on     

Evaluation of friction coefficient using indentation model of Brinell hardness test for sheet metal forming

This work presents an indentation model of the Brinell hardness test, which is a rigid ball-deformable plane contact model (RB-DP model), to elucidate the sliding friction mechanism of sheet metal forming. In the proposed model, the friction force can be defined as a combination of shear (shearing effect) and plough (ploughing effect) forces. The real contact area ratio α is determined from the RBDP model under sliding condition. Moreover, the lateral contact area ratio A _c /A _r can be specified as a function of the real contact area ratio α. Based on Meyer’s law and Hertz contact problem, the maximum contact area ratio α _u , a limiting condition of the real contact area ratio α, can be described as a function of the strain hardening exponent n. Additionally, a limiting condition applies: the strain hardening exponent n must be less than 0.64 in the present model. The present friction model reveals that the friction coefficient μ _d is a function of strain hardening exponent n, the real contact area ratio α and the maximum contact area ratio α _u . The calculated friction coefficient μ _d agrees with the published experimental results.     

A friction model for microforming

For the simulation of metal forming processes, input data relating to the tool–workpiece interface is necessary. For microforming applications, this input data becomes very much more critical and traditional methods are not realistic. This paper describes an approach that seeks to describe friction by modelling the geometric surface roughness of the tool. This finite-element-based model has been validated experimentally in terms of loads and metal forming using the ring test and actual surface measurements. It enables more accurate and also more flexible modelling of friction.     

Stability criterion for stick-slip motion using a discontinuous dynamic friction model

An analysis of stick-slip stability is presented using a discontinuous friction model which consists of a negative damping action for the slip acceleration phase and a constant frictional resistance for the slip deceleration phase. Limiting conditions for stability due to a positive viscous damping action are defined, where transition from self-generated vibrations to smooth sliding occurs. The implications of the theory are discussed for the design and analysis of equipment subject to such vibrations.     

Analytical and numerical study on plastic instabilities for axisymmetric tube bulging

In this paper, plastic instabilities of elasto–plastic tubes subject to internal pressure are discussed. For diffuse necking prediction, the classical intrinsic criteria for diffuse necking are accurate for long cylindrical tubes. However, for short tubes, geometric changes are important, and the intrinsic criteria become insufficient. For this purpose, a new diffuse necking criteria is proposed including geometric effects in the prediction.On the other hand, for the local necking prediction, the Hill's criterion is not accurate for short tubes, due to the biaxial stretching. As an alternative, a local necking criterion based on a modified Hill's assumption for localized necking is proposed. The numerical calculations carried out for different tube dimensions, explains the geometrical effects on the localization of deformations for pressurized tubes, and improves the accuracy of the proposed criteria.     

固体颗粒介质成形新工艺试验研究与应力分析

自行设计制造了固体颗粒介质传压性能试验与测试装置,通过试验测得到了固体颗粒的传压规律.建立了板料在拉深力作用下的两种力学模型:线性分布载荷和二次函数分布载荷的力学模型.自行设计制造了板料成形试验模具与装置,通过对成形试验件的测量与分析,建立了自由变形抛物线函数变形模型.对固体颗粒介质板料拉胀成形未贴模时塑性变形阶段进行了塑性变形分析,推导出了自由变形区的应力分布计算公式,为固体颗粒介质板料拉胀成形塑性理论研究奠定了基础.     

3D Analysis of cold rolling using a constitutive model for interface friction

Full three-dimensional numerical analyses are carried out for the cold rolling of plates of finite width, to study the effect of the width spread during rolling. The contact and friction between roll and plate is modeled in terms of an interface constitutive model that accounts for the friction forces in the rolling direction as well as those in the transverse direction that give resistance to the width spread. At low normal pressures Coulomb friction is represented while at high normal pressure a yield stress limitation of the maximum tangential stress is incorporated, and slip as well as no slip is accounted for. Finite strain elasto-plasticity is applied for the plate material, using mostly isotropic hardening or in a few cases kinematic hardening to represent the effect of a rounded vertex on the yield surface. In addition, for a given plate thickness and degree of reduction the effect of different values of the roll radius and the effect of different values of the plate width are analysed.     

管材成形技术综述

与板材一样，管材也是工业生产中广泛使用的重要原料。随着技术的进步，各种管材加工技术得到了快速发展。其中，具有低能耗、省材料、高效率等优点的塑性成形，逐渐成为管材加工的主要手段。本文以广泛应用的典型管成形工艺方法为重点，介绍了各种管成形的工艺、设备等内容。     

A simple model to simulate electromagnetic sheet free bulging process

Electromagnetic sheet forming is a high-velocity forming process driven by the coupled electromagnetic and mechanical phenomena. The deformation of the workpiece is governed by the body forces (Lorentz forces) that results from a pulsed magnetic field produced by a flat spiral coil. Formability can be increased using this high-velocity forming technique due to the inertial forces and high strain rates. In this study, we consider the electromagnetic and the mechanical aspect of the process as two independent problems. The finite difference method has been employed to solve the electromagnetic equations. The pressure acting on the sheet and due to the Lorentz forces is estimated neglecting the influence of the sheet velocity on the magnetic field. Then it has been treated as a load in the mechanical problem. Numerical simulations of the mechanical problem have been performed with the commercial finite element code ABAQUS/Explicit. The magnetic pressure has been introduced in ABAQUS/Explicit as an analytical pressure distribution. The general objective of this study is to better understand the complex phenomenon of deformation and the influence of viscoplastic material behaviour during the simulation of a free bulging electromagnetic sheet forming process.     

A soft configuration model for wearless sliding friction

A phenomenological model of soft potential configurations is proposed to describe sliding friction in the wearless regime. This model accounts for the static and dynamic behavior. The physical origin of the logarithmic speed or time dependence for the friction coefficient is described. Means to control the friction coefficient by controlling the soft defect density are discussed. This revised version was published online in September 2006 with corrections to the Cover Date.     

A model of friction for a pin-on-disc configuration with imposed pin rotation

A friction model is developed by considering the Coulomb friction model, a probabilistic approach of wear prediction, the kinematics of the pin-on-disc configuration and the elastic theory of bending. The model estimates the magnitude and direction of the frictional force, the pin torque, the probability of asperity contact and the real area of contact distinguishing between the part due to elastic and plastic asperity contacts respectively. Therefore, the proposed model is suitable for the prediction of adhesive wear. It can be applied to metal contacts for conductance characterisation through the plastically deformed asperities which is of great interest for electrical contact resistance studies.     

Study of the static coefficient of friction of fishing cordage on a friction gear drum

Fiction interaction of fishing cordage and a friction gear drum under the preliminary displacement on the contact arc by 40–720° is studied. In all experiments, similar pressure of the cordage on the drum surface is ensured. Formulas for the static coefficient of friction are obtained for any angle of the contact arc. The results make it possible to increase the accuracy of calculation of the pulling characteristics of friction gear mechanisms.     

A method for forming a single metal nanowire using track membrane templates

A new electrochemical method for forming single metal nanostructures (nanowires) is described. A standard track membrane with statistically distributed etched high-density channels is used as a template. A few track membranes are stacked in a multilayer sandwich and tightly pressed to each other and to a metal substrate-cathode. Metal is electrochemically deposited into the through etched channels of the track membranes. Since the probability of statistically distributed etched through channels in a sandwich of track membranes being butted together is rather low, etched channels with electrochemically deposited metal decrease in number in each subsequent track membrane, beginning with the substrate-cathode, until a single nanostructure is formed in the top track membrane.     

A friction model for dry contacts during metal-forming processes

In a metal-working process, the friction between the material and the tools influences the process by modifying the strain distribution of the workpiece. This frictional behavior is often taken into account by using a constant coefficient of friction in the finite element simulations. However, friction coefficient varies in time and space with many parameters. This paper aims at modeling of friction in dry contacts which happens at metal-forming processes in the lack of lubricant. The coefficient of dry friction in this model is a function of contact area ratio (which is a function of surface contact characteristics) and strain hardening exponent (material property). The V-bending process of aluminum alloy 6061-T4 sheets was studied experimentally and numerically using ABAQUS/Standard with two kinds of friction models: Coulomb friction and newly developed dry friction models. The results clearly showed that the developed dry friction model has better results in predicting load-stroke curves and springback compared to traditional Coulomb friction model. The FE prediction error for 6061-T4 AA is 16.9% using Coulomb friction model and 9.2% using dry friction model.     

High speed disk friction losses in a gaseous medium

In the context of a feasibility study of a very high-speed turbocompressor for a synthesis gas, disk friction losses were regarded as significant. The previous theory for disk losses by Daily and Nece was supported by experimental results for disks rotating at modest rotary speeds in liquids. This paper describes some experiments with disks (127 mm dia.) rotating at high rotary speeds (up to 1100 rev/sec) in air.The results are compared with the previous theory. Good correlation was obtained for relatively small axial clearance ratios ( and 0·0124). However, for a larger axial clearance ratio ( ) the correlation between the results and the earlier theory was poor.Recommendations are made relevant to design calculations for disk losses in high-speed turbomachinery for gases.     

镶嵌型固体自润滑滑动轴承的摩擦磨损探讨

介绍了金属基镶嵌型固体自润滑滑动轴承在高温下的摩擦特性，分析了这种轴承的磨损机理，并提出在高温及锻压设备上应用的建议。     

Prediction of failure in tube hydroforming process using a damage model

In tube hydroforming process (THP), two types of loading, internal pressure and axial feeding and in particular the combination of them, are needed to feed the material into the cavities of the die to form the workpiece into the desired shape. If the variation of pressure versus axial feeding is not determined properly, the workpiece may be buckled, wrinkled or burst during THP. The appropriate variation is normally determined by experiment which is expensive and time-consuming. In this work, numerical simulation using Johnson-Cook models for predicting the elasto-plastic response and the failure of the material are employed to obtain the best combination of internal pressure and axial feeding. The numerical simulations are examined by a number of experiments conducted in the present investigation. The results show very close agreement between the numerical simulations and the experiments, suggesting that the numerical simulations using Johnson-Cook material and failure models provide a valuable tool to examine the different parameters involved in THP.