Image analysis of sheet metal surfaces

The analysis of a sheet metal surface is essential to describe phenomena like friction or varnishing ability. As 2D measurements are not sufficient for a full understanding of the surface performance, 3D image analysis methods are performed to characterise the topography of rough surfaces. In this paper some investigations are presented concerning the lubrication area and the material cut spots of a St14 sheet surface. To consider relevant aspects for metal forming, roughness measurements have been performed with elongated and loaded sheets. The evolution of the surface structure is essential to understand effects like the lubricated friction or the contact between the paint and rough surfaces.     

Friction drive of an SAW motor. Part III: modeling

A 2-layer modeling method of friction drive of a surface acoustic wave motor is proposed. The surface layer accounts for the previously proposed point-contact friction drive model, which was generalized to correspond spatially to the underlying layer that is comprised of a 3-D elasticity field. A method to determine stiffness through the use of analytical solutions of 3-D contact problems bridges the 2 layers. Because the determined stiffness expresses the accuracy of the results regarding either layer, the validity of the results concerning the stiffness and the resulting stress field was evaluated by comparison with the results of finite element analysis. Furthermore, we executed numerical simulations by using the friction drive model, which were compared with the measured displacements of the frictional surface of the slider. The simulation accurately represented the normal displacement of the frictional surface; the modeling procedure in the normal direction was found to be reliable. However, because the friction coefficient drastically changes the tangential displacement, we could not discuss the reliability of the modeling procedure in the tangential direction. A thorough discussion of the friction drive would thus require further investigation of the friction phenomena.     

Role of tool-part interaction in process-induced warpage of autoclave-manufactured composite structures

The role of tool-part interaction in process-induces warpage of a large composite structure was studied using a three-dimensional process model, developed by integrating sub-models that describe the evolution of cure and properties of composite as well as various physical phenomena encountered, during autoclave processing. The process model was implemented through user sub-routines interfaced with the finite element software, ABAQUS. The tool-part interaction during processing was modeled using contact elements. The predicted temperature and warpage of an aircraft part, using a frictional tool-part interface and experimentally measured cure-dependent tool-part interfacial friction coefficients, compared very well with experimental temperature and warpage, validating the 3-D process model. A comparison of predictions using various models for the tool-part interface suggests that the two components of tool-part interaction that contribute to warpage are change in shape of the tool and part, and process-induced stress caused by constrained deformation of the tool and the part.     

From measurements of hydrodynamics to computation of species transport in falling films

Falling films on horizontal tube banks are widely used in absorption heat pumps. Liquid film heat and mass transfer models in the literature are based on simplistic assumptions about such flows. Droplets forming under the tubes fall on subsequent tubes, and the ensuing waviness and mixing on the liquid film affect absorption. High-speed flow visualization, image analysis, and computations are used to understand the effect of hydrodynamics on local absorption phenomena. Image analysis mathematically describes the interface, and the surface area and volume of the droplets. These flows are also numerically analyzed using the volume-of-fluid method for the liquid–vapor interface. The 3-D model corroborates with high fidelity the droplet formation, detachment and impact observed in experiments. Fully resolved 3-D computations of the coupled fluid flow and heat and mass transfer reveal the local gradients and transfer rates, and their spatial and temporal variations in the falling-film and inter-tube regions.     

Role of Friction in Cold Ring Rolling

1. Introduction Cold ring rolling is a main technology used to manu- facture various precise seamless ring shape parts. It has been increasingly used in many industrial fields such as bearing, machine, automobile, petrochemicals, aeronau- tics, astronautics and atomic energy because of its many technical superiorities such as considerable saving in en- ergy and material cost, high quality, high efficiency, and low noise, etc. To research and develop advanced precise cold ring rolling technolog…     

Modeling of hot isostatic pressing of metal powder with temperature–dependent cap plasticity model

In this paper, the coupled thermo–mechanical simulation of hot isostatic pressing (HIPing) is presented for metal powders during densification process. The densification of powder is assumed to occur due to plastic hardening of metal particles. The constitutive model developed is used to describe the nonlinear behavior of metal powder. The numerical modeling of hot powder compaction simulation is performed based on the large deformation formulation, powder plasticity behavior, and frictional contact algorithm. A Lagrangian finite element formulation is employed for the large powder deformations. A modified cap plasticity model considering temperature effects is used in numerical simulation of nonlinear powder behavior. The influence of powder-tool friction is simulated by the use of penalty approach in which a plasticity theory of friction is incorporated to model sliding resistance at the powder-tool interface. Finally, numerical examples are analyzed to demonstrate the feasibility of the proposed thermo–mechanical simulation using the modified cap plasticity model in the hot isostatic forming process of powder compaction.     

Numerical investigation of the influence of frictional conditions in thread rolling operations with flat dies

Numerical simulation technology has become an important part of the process design stage in bulk metal forming operations. With increasing computing performance, three dimensional simulations within the product design process are thus becoming increasingly feasible. However, the modeling of friction within numerical simulations is still posing a challenge, especially in very friction sensitive processes, such as rolling of axisymmetric parts. Within the presented work, the process of rolling with flat dies with consideration of friction (according to Amontons-Coulomb) is simulated and analyzed. With the developed model, tribological loads as well as the influence of friction is investigated. These numerical findings are contrasted with experimental results obtained with an industrial forming machine. It is shown that the numerically obtained results are highly sensitive regarding numerical and physical contact modeling parameters. This is due in part to the highly varying frictional conditions (relative sliding velocity, contact normal stress) within the contact zone. Additionally, it is shown that the contact zone exhibits properties that favor static friction rather than sliding friction. This observation is especially important for an adequate empirical characterization of friction for thread and profile rolling processes.     

非连续粗糙多界面接触变形和能量损耗特性研究

非连续多层叠加结构的粗糙界面接触形变与能量损耗特性一项研究较少的难题。本文在单一界面能量损耗特性研究的基础上,通过建立“多层粗糙金属板--刚性平面”的多界面模型,采用有限元方法,对加载与卸载过程中,具有不同界面形貌、不同塑性变形行为和界面摩擦的多层叠加模型粗糙多界面的接触力和变形进行计算,研究了多层叠加结构粗糙界面上的接触力-变形关系,以及由塑性变形与界面摩擦引起的能量损耗特性,构造了描述粗糙多界面上接触力-变形关系表达式,计算了多层粗糙界面的能量传递损耗率,分析了多层叠加结构的非连续粗糙多界面接触变形机理和能量损耗特性。     

2D adaptive mesh methodology for the simulation of metal forming processes with damage

In this work, a fully adaptive 2D numerical methodology is proposed in order to simulate with accuracy various metal forming processes. The methodology is based on fully coupled advanced finite strain constitutive equations accounting for the main physical phenomena such as large plastic deformation, non-linear isotropic and kinematic hardening, ductile isotropic damage and contact with friction. The adaptivity concerns the space discretization using FEM as well as the applied loading sequences. Mesh size distribution is based on various error indicators making use of the hessian of the plastic strain rate combined with a specific damage error function and a specific local curvature error function evaluated at contact boundaries. 2D mesh size can be refined or coarsened when necessary according to these error indicators. Particularely, the smallest size is found to be inside the zones where the damage is highly active. The applied loading paths are also adaptively decomposed into various sequences depending on both number and size of the fully damaged elements. The adaptive procedure is validated through various sheet and bulk metal forming examples. In this paper, a plane stress tensile test, an axisymmetric blanking process of two materials with different ductilities and a cold extrusion process are presented.     

反向压力对板材粘性介质压力胀形的影响研究

为研究带有反向压力粘性介质压力胀形过程中接触条件对板材成形性的影响规律,利用DEFORMTM-2D结合韧性断裂准则对覆层板粘性介质压力胀形过程进行有限元分析.结果表明:接触表面无摩擦单纯依靠反向压力能够提高板材成形极限,随着接触表面摩擦系数增大,板材壁厚分布愈均匀,板材的破裂位置由试件顶端转移到凹模圆角处,板材成形极限显著提高.因此,在三维应力状态下有效控制板材所受法向压力和界面摩擦力可以提高板材成形性.     

Modeling effects of gas adsorption and removal on friction during sliding along diamond-like carbon films

In this paper, the physical and tribochemical processes that occur in a sliding contact between two diamond-like-carbon (DLC)-coated counterparts are discussed. The applicability of some of the most cited of the adsorption kinetics equations for modeling the gas adsorption process when environment molecules form bonds to the surface are examined. The process modeling is also discussed when part of the adsorbate is removed due to rubbing the surface by a slider. A direct connection between a kind of molecular friction and gradual wear is established. The models are compared with some recent experimental results. The present computer simulations of the adsorption and mechanical desorption of oxygen help to explain how microscopic processes, such as the breaking and forming of interatomic bonds, may affect macroscopic phenomena such as friction. In particular, it is shown that the initial roughness of the DLC surface may have a considerable influence on the probability of breaking bonds during mechanical removal of adsorbate and on the process of the gradual tribochemical wear of DLC films.     

低频振动对塑性成形表面微观形貌的影响

目的 通过对塑性成形界面施加纵向和法向低频振动,探究不同振动参数对成形过程中表面质量的影响规律。方法 采用自主设计的低频振动发生器完成纵向振动作用下的摩擦实验和法向振动作用下的压缩实验,统计材料表面变形区域的平均粗糙度,评价成形质量。结果 在干摩擦条件下,不同频率（0～50 Hz）的纵向小振幅（0.1mm）振动有利于提高成形界面的表面质量,变形区域的表面粗糙度与频率成反比,但是较大振幅（0.4 mm）的纵向振动会增加接触面的材料磨损,降低表面质量;不同频率（0～50 Hz）和不同振幅（0～0.4 mm）的法向振动均有利于提高干摩擦成形界面的表面质量,在0.2 mm振幅条件下表面粗糙度下降最为明显,振幅超过0.2mm后,增加振幅对提升表面质量的影响不明显。结论 低频振动对成形界面微观形貌影响较大,合理优化低频振动工艺参数可显著提高成形界面的表面质量。     

基于数值仿真的冲压成形界面接触压力

为探究冲压成形过程中板料-凹模圆角区界面接触压力,采用有限元静力算法建立了U形件小圆角半径弯曲成形过程的数值仿真模型,完成了板料和模具界面接触压力数值模拟,并参数分析了钢板强度、相对圆角半径、压边力和摩擦系数对板料界面接触压力分布的影响.研究表明:与压边力和摩擦系数相比,钢板强度和相对圆角半径更明显地影响着板料界面接触压力,并随着材料强度增加和相对模具圆角半径减小界面接触压力明显增加;随着压边力和摩擦系数的增加,界面接触压力宽度也随之增大.     

Formation of a Nanophase Wetting Layer and Metal Growth on a Semiconductor

Based on the data on the atomic density of a film and degree of its homogeneity during the formation of the interface between 3d transition metals (Cr, Co, Fe, or Cu) and silicon, a new concept of forming a contact between a reactive metal and a semiconductor has been justified. According to this concept, the low-temperature vapor-phase deposition of a metal onto a semiconductor is accompanied by the formation of a two-dimensional nanophase wetting layer of a metal or its mixture with silicon with a thickness of several monolayers, which significantly affects the interface formation and structure. This concept changes a perspective of forming a contact between a metal and a semiconductor substrate: it is necessary to take into account not only the formation of surface phases and clusters and/or the mixing process, but also the effect of elastic wetting of a substrate by the forming phases.     

Augmented reality user interface for an atomic force microscope-based nanorobotic system

A real-time augmented reality (AR) user interface for nanoscale interaction and manipulation applications using an atomic force microscope (AFM) is presented. Nanoscale three-dimensional (3-D) topography and force information sensed by an AFM probe are fed back to a user through a simulated AR system. The sample surface is modeled with a B-spline-based geometry model, upon which a collision detection algorithm determines whether and how the spherical AFM tip penetrates the surface. Based on these results, the induced surface deformations are simulated using continuum micro/nanoforce and Maugis-Dugdale elastic contact mechanics models, and 3-D decoupled force feedback information is obtained in real time. The simulated information is then blended in real time with the force measurements of the AFM in an AR human machine interface, comprising a computer graphics environment and a haptic interface. Accuracy, usability, and reliability of the proposed AR user interface is tested by experiments for three tasks: positioning the AFM probe tip close to a surface, just in contact with a surface, or below a surface by elastically indenting. Results of these tests showed the performance of the proposed user interface. This user interface would be critical for many nanorobotic applications in biotechnology, nanodevice prototyping, and nanotechnology education.     

混合润滑状态下结合面的法向接触刚度研究

针对润滑条件下机械结合面的接触特性受油膜影响的问题,基于结合面接触刚度由油膜接触刚度和固体表面接触刚度组成的思想,建立混合润滑状态下结合面的法向接触刚度模型。采用三维的Weierstrass-Mandelbrot函数获得具有分形特征的粗糙表面,并基于统计学方法建立干摩擦条件下结合面的法向接触刚度模型,考虑了微凸体的完全弹性变形、弹塑性变形以及完全塑性变形过程。在此基础上,求解了油膜的等效厚度并建立油膜的接触刚度模型。结果表明:结合面的法向接触刚度随法向载荷的增加而增加,且混合润滑状态下结合面的接触刚度大于干摩擦条件下结合面的接触刚度;该模型避免了油膜厚度测量难的问题,为机械结构的润滑状态预测提供了帮助。     

Extension of the node‐to‐segment contact element for surface‐expansion‐dependent contact laws

A class of friction laws depending on the measure of contact surface expansion is defined in the paper within the continuum contact mechanics framework. The nominal and spatial forms of constitutive relations are discussed, including incremental penalty relations. Further, an extended node‐to‐segment element is derived which is capable of treating surface‐expansion‐dependent contact laws in a consistent way. The approach is suitable for any kind of node‐to‐segment contact elements. Finally, the computational efficiency of the extended element as well as other possible approaches are illustrated by numerical examples relevant to metal forming applications. Copyright © 2001 John Wiley & Sons, Ltd.     

An approximate bending force prediction for 3-roller conical bending process

Roll bending process is an important metal forming process used to produce cylindrical and conical shells and sections for various applications. 3-roller conical bending is one such process. For this process it is important to evaluate the maximum force acting on the rollers during the rolling process for designing the rolling machine as well as for evaluating the coefficient of friction at roller-plate interface. It is observed that maximum force is acting on the roller during the static bending in roll bending process [Gandhi et al. 2008]. In the present study mathematical model for force prediction on the rollers have been developed. Effects of various material properties and geometrical parameters have been studied. It has been concluded that the proposed model can be effectively used to get the roller bending force for given geometrical parameters and material properties. It can also be used to get roller plate interface friction, if the experimental value of roll bending force is available.     

Teleoperated 3-D Force Feedback From the Nanoscale With an Atomic Force Microscope

In this study, 3-D experimental teleoperated force feedback during contact with nanoscale surfaces is demonstrated using an atomic force microscope (AFM) on the slave side and a haptic device on the master side. To achieve 3-D force feedback, coupling between one of the horizontal forces and the vertical force is a crucial bottleneck. To solve this coupling issue, a novel force decoupling algorithm is proposed. This algorithm uses local surface slopes, an empirical friction force model, and the haptic device motion angle projected onto the surface to estimate the friction value during experiments. With this estimation, it is possible to decouple the three orthogonal forces acting on the tip of the AFM cantilever. Moreover, using an adaptive observer, parameters of the friction model can be changed online, removing the necessity to calibrate the friction model initially. Finally, a modified passivity-based bilateral control is used to reflect the scaled nanoscale forces to the master side and the operator. The performance of the system is demonstrated on experimental results for flat and non-flat, and hard and soft surfaces.