Fully Coupled Frictional Contact Using Elastic Halfspace Theory

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
K. Willner
Keyword(s):  
Frictional Contact ◽  
Numerical Models ◽  
Normal Load ◽  
Friction Pair ◽  
Contact Problems ◽  
Elastic Halfspace ◽  
Real Area Of Contact ◽  
Fully Coupled ◽  
Real Area

The effect of dry metallic friction can be attributed to two major mechanisms: adhesion and ploughing. While ploughing is related to severe wear and degradation, adhesion can be connected to pure elastic deformations of the contacting bodies and is thus the predominant mechanism in a stable friction pair. The transmitted friction force is then proportional to the real area of contact. Therefore, a lot of effort has been put into the determination of the fraction of real area of contact under a given load. A broad spectrum of analytical and numerical models has been employed. However, it is quite common to employ the so-called Mindlin assumptions, where the contact area is determined by the normal load only, disregarding the influence of friction. In the subsequent tangential loading, usually the contact pressure distribution is kept fixed such that the coupling between the tangential and normal solutions is neglected. Here, a numerical solution scheme based on elastic halfspace theory for frictional contact problems is presented where full coupling between the normal and tangential tractions and displacements is taken into account. Several examples show the influence of the coupling effects, but also the limitations for the analysis of rough contacts.

Determination of Adhesion Forces Between Smooth and Structured Solids

2012 ◽  
Author(s):  
Hartmut R. Fischer ◽  
Edwin R. M. Gelinck
Keyword(s):  
Adhesion Force ◽  
Smooth Surfaces ◽  
Adhesion Forces ◽  
Real Area Of Contact ◽  
Study Results ◽  
Colloidal Probes ◽  
Good Agreement ◽  
Real Area

The tendency of smooth surfaces to stick spontaneously to each other is becoming a serious problem, with: a) the increasing quality in surface finish for many components and systems, b) on miniaturization in mechanical components, and c) in demanded precision of positioning of parts in high-end equipment machines and systems. Surfaces tend to be made smoother in order to gain flatness or in order to fulfill the need for more precise and reproducible positioning of parts. Adhesion or even sticking of the surfaces is a major showstopper for these applications. There are several measures that can be taken in order to reduce spontaneous adhesion. Quantification of the effectiveness of the chosen solution is most often done using an AFM with probes varying from 1 nm to 8 micron of contact diameter. A serious disadvantage in measuring adhesion by sharp tips is the wear of the tips. Sharp tips wear easily, resulting in undefined contact areas. When the real area of contact is not well defined, the quantification of the adhesion force is not significant. In the current study results of AFM measurements from literature with different tip diameters of colloidal probes are compared with measurements we performed using AFM cantilevers with a plateau tip and using probes from large spheres using an alternative setup (UNAT). These methods give results that are in good agreement with values found in literature. Large contacting surface enhance the quality of the measured adhesion values. Another part of the study deals with a deliberately roughening of smooth surfaces to minimize (spontaneous) adhesion. Good agreement has been found with existing results. For the use of larger surfaces it is important that the surfaces to be tested are extremely clean. Particles on smooth surface do influence the measurements quite easily. Especially for larger areas, the possibility of encountering particles on the surface are more likely, when particles are present. For the measurements in this study a lot of care has been taken therefore to remove contamination: particles as well as contamination of organic origin.

Multi-Scale Contact Modeling of Coated Steels for Sheet Metal Forming Applications

2018 ◽  
Vol 767 ◽  
pp. 223-231 ◽  
Author(s):  
Meghshyam Shisode ◽  
Javad Hazrati ◽  
Tanmaya Mishra ◽  
Matthijn de Rooij ◽  
Ton van den Boogaard
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Normal Load ◽  
Steel Substrate ◽  
Surface Textures ◽  
The Real ◽  
Multi Scale ◽  
Real Area Of Contact ◽  
Real Area

Friction in sheet metal forming is a local phenomenon which depends on continuously evolving contact conditions during the forming process. This is mainly influenced by local contact pressure, surface textures of the sheet metal as well as the forming tool surface profile and material behavior. The first step for an accurate prediction of friction is to reliably estimate real area of contact at various normal loads. In this study, a multi-scale contact model for the normal load is presented to predict asperity deformation in coated steels and thus to estimate the real area of contact. Surface profiles of the zinc layer and steel substrate are modelled explicitly obtained from confocal measurements. Different mechanical properties are assigned to the zinc coating and the steel substrate. The model was calibrated and validated relative to lab-scale normal load tests using different samples of zinc coated steel with distinct surface textures. The results show that the model is able to predict the real area of contact in zinc-coated steels for various contact pressures and different surface textures. Current multi-scale model can be used to determine the local friction coefficient in sheet metal forming processes more accurately.

Paper 42: Preliminary Study of the Influence of Stress and Deformation in the Substrate on Junction Growth and Friction

1967 ◽  
Vol 182 (11) ◽  
pp. 152-161 ◽  
Author(s):  
B. Fogg
Keyword(s):  
Bulk Material ◽  
Normal Load ◽  
Large Change ◽  
Real Area Of Contact ◽  
Biaxial Tensile Stress ◽  
Constant Normal Load ◽  
Preliminary Study ◽  
Stress States ◽  
Stress And Deformation ◽  
Real Area

The change in surface texture and the associated increase in ‘real’ area of contact at the surface in contact with the punch during stretch forming is very much greater than that predicted by Tabor's theory. It was suggested initially that this large change could be due to the effect of the biaxial tensile stress in the bulk material. Subsequent tests on model asperities show that the pressure to cause yielding of the asperities is reduced when tensile stresses are present in the bulk material resulting in a larger ‘real’ area of contact for a given normal load. However, an even greater increase in contact area is produced if the bulk material is allowed to deform plastically during the application of a constant normal load. Other stress states were examined on a basis of indentation testing. It is suggested that the greatly reduced apparent yield pressure of the asperities gives rise to high friction coefficient over the punch nose. Application of Tabor's theory, together with the already large initial real area of contact, seems to account for the observed large junction growth.

The use of static reduction in the finite element solution of two-dimensional frictional contact problems

2013 ◽  
Vol 228 (9) ◽  
pp. 1474-1487 ◽  
Author(s):  
A Thaitirarot ◽  
RC Flicek ◽  
DA Hills ◽  
JR Barber
Keyword(s):  
Finite Element ◽  
Stiffness Matrix ◽  
Frictional Contact ◽  
Contact Problems ◽  
Computational Time ◽  
Friction Laws ◽  
Periodic Loading ◽  
Frictional System ◽  
Well Posed

In this paper, detailed instructions are given for performing static reduction on a finite element description of an elastic contact problem, thus reducing the dimensionality of the problem to the set of contact nodes alone. This significantly reduces the computational time for the solution to evolutionary contact problems and also gives the user greater control over the detailed implementation of the contact and friction laws. The reduced stiffness matrix is also an essential ingredient in the determination of the critical coefficient of friction for the problem to be well posed, and it facilitates the determination of the conditions under which a frictional system may shake down under periodic loading.

scholarly journals Analysis of the Evolution of the Structure of a Surface With Pyramidal Asperities in Contact With a Hard and Smooth Plane

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Bensaad Bourassia ◽  
Bourouga Brahim
Keyword(s):  
Reference Model ◽  
Contact Point ◽  
Thermal Contact ◽  
Measurement Techniques ◽  
Theoretical Models ◽  
Real Area Of Contact ◽  
Smooth Plane ◽  
Contact Parameters ◽  
Real Area

Abstract This research deals with the evolution of the structure of the sapphire–brass interface due to the variation of contact pressure. This evolution primarily affects the essential parameters that govern the thermal contact resistance (TCR), namely, the contact point density N, the ratio of real area of contact S*, and the distance d separating the median contact planes. The combination of three measurement techniques, namely, profilometry, imaging, and mechanical characterization, was used for the purpose of investigating the structural variation of the interface. Alternatively, the TCR, which prevails at the interface, was estimated. Thus, the object of our study is to propose an original and new experimental approach allowing at the same time the precise measurement of the TCR and the estimate of the contact parameters of the interface studied constituting input data to the theoretical models of TCR. The estimated values given by these last are then compared with those measured. Through this approach, we try to open new ways of experimentation that would tend to reinforce the effort of TCR modeling. The results obtained showed that the roughness parameters Ra and Rq are independent of loading. The roughness Rp, which is considered equal to d, is sensitive to loading and has the same decreasing behavior under the effect of loading. The determination of S*, using the hardness testing, is even more relevant when the effective hardness Hc is considered. Analysis of data for the estimation of the TCR shows that the comparisons with the reference model (Bardon) attest to the relevance of our approach.

scholarly journals Evolution of real area of contact due to combined normal load and sub-surface straining in sheet metal

Friction ◽  
2020 ◽  
Author(s):  
Meghshyam Shisode ◽  
Javad Hazrati ◽  
Tanmaya Mishra ◽  
Matthijn De Rooij ◽  
Ton Van Den Boogaard
Keyword(s):  
Sheet Metal ◽  
Friction And Wear ◽  
Normal Load ◽  
Contact Forces ◽  
Surface Strain ◽  
Material Behavior ◽  
The Real ◽  
Real Area Of Contact ◽  
Macro Scale ◽  
Real Area

Abstract Understanding asperity flattening is vital for a reliable macro-scale modeling of friction and wear. In sheet metal forming processes, sheet surface asperities are deformed due to contact forces between the tools and the workpiece. In addition, as the sheet metal is strained while retaining the normal load, the asperity deformation increases significantly. Deformation of the asperities determines the real area of contact which influences the friction and wear at the tool-sheet metal contact. The real area of contact between two contacting rough surfaces depends on type of loading, material behavior, and topography of the contacting surfaces. In this study, an experimental setup is developed to investigate the effect of a combined normal load and sub-surface strain on real area of contact. Uncoated and zinc coated steel sheets (GI) with different coating thicknesses, surface topographies, and substrate materials are used in the experimental study. Finite element (FE) analyses are performed on measured surface profiles to further analyze the behavior observed in the experiments and to understand the effect of surface topography, and coating thickness on the evolution of the real area of contact. Finally, an analytical model is presented to determine the real area contact under combined normal load and sub-surface strain. The results show that accounting for combined normal load and sub-surface straining effects is necessary for accurate predictions of the real area of contact.

Variational analysis of fully coupled electro-elastic frictional contact problems

2010 ◽  
Vol 283 (9) ◽  
pp. 1314-1335 ◽  
Author(s):  
Stanislaw Migorski ◽  
Anna Ochal ◽  
Mircea Sofonea
Keyword(s):  
Variational Analysis ◽  
Frictional Contact ◽  
Contact Problems ◽  
Fully Coupled

Elastoplastic Frictional Contact Study on Interference Fits of Compressor

2011 ◽  
Vol 211-212 ◽  
pp. 535-539
Author(s):  
Ai Hua Liao
Keyword(s):  
Stress Distribution ◽  
Contact Stress ◽  
Frictional Contact ◽  
Contact Problems ◽  
Boundary Problems ◽  
Interference Fit ◽  
Parametric Variational Principle ◽  
Design And Manufacturing ◽  
Contact Stress Distribution ◽  
Fit Tolerance

The impeller mounted onto the compressor shaft assembly via interference fit is one of the key components of a centrifugal compressor stage. A suitable fit tolerance needs to be considered in the structural design. A locomotive-type turbocharger compressor with 24 blades under combined centrifugal and interference-fit loading was considered in the numerical analysis. The FE parametric quadratic programming (PQP) method which was developed based on the parametric variational principle (PVP) was used for the analysis of stress distribution of 3D elastoplastic frictional contact of impeller-shaft sleeve-shaft. The solution of elastoplastic frictional contact problems belongs to the unspecified boundary problems where the interaction between two kinds of nonlinearities should occur. The effect of fit tolerance, rotational speed and the contact stress distribution on the contact stress was discussed in detail in the numerical computation. The study play a referenced role in deciding the proper fit tolerance and improving design and manufacturing technology of compressor impellers.

scholarly journals Sensitivity Analysis for Frictional Contact Problems with Large Deformation.

1999 ◽  
Vol 65 (637) ◽  
pp. 1859-1866
Author(s):  
Xian CHEN ◽  
Kazuhiro NAKAMURA ◽  
Masahiko MORI ◽  
Toshiaki HISADA
Keyword(s):  
Sensitivity Analysis ◽  
Large Deformation ◽  
Frictional Contact ◽  
Contact Problems
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