Home About us Contact
|
Home About us Contact | ||
|
|
||
Contact Mechanics (contact + mechanic)
Selected AbstractsBi-Stable Adhesion of a Surface with a DimpleADVANCED ENGINEERING MATERIALS, Issue 5 2010Robert M. McMeeking In this paper, we propose a new adhesive system of dimpled surfaces. The principle is derived from a contact mechanics model. The material is assumed to be linear elastic and isotropic, and attraction between the surfaces of the half-spaces is modeled via the concept of a specific adhesion energy. It is found that large and small detachments are unstable and will either grow or shrink spontaneously when their sizes are perturbed. It is shown that this phenomenon can lead to a new bi-stable adhesive system in which weak adhesion can be converted to strong adhesion by the application of pressure. [source] A contact algorithm for frictional crack propagation with the extended finite element methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2008Fushen Liu Abstract We present an incremental quasi-static contact algorithm for path-dependent frictional crack propagation in the framework of the extended finite element (FE) method. The discrete formulation allows for the modeling of frictional contact independent of the FE mesh. Standard Coulomb plasticity model is introduced to model the frictional contact on the surface of discontinuity. The contact constraint is borrowed from non-linear contact mechanics and embedded within a localized element by penalty method. Newton,Raphson iteration with consistent linearization is used to advance the solution. We show the superior convergence performance of the proposed iterative method compared with a previously published algorithm called ,LATIN' for frictional crack propagation. Numerical examples include simulation of crack initiation and propagation in 2D plane strain with and without bulk plasticity. In the presence of bulk plasticity, the problem is also solved using an augmented Lagrangian procedure to demonstrate the efficacy and adequacy of the standard penalty solution. Copyright © 2008 John Wiley & Sons, Ltd. [source] On the convergence of stationary sequences in topology optimizationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2005Anton Evgrafov Abstract We consider structural topology optimization problems including unilateral constraints arising from non-penetration conditions in contact mechanics. The resulting non-convex non-smooth problems are instances of mathematical programs with equilibrium constraints (MPEC), or bi-level programs. Applying nested (implicit programming) algorithms to this class of problems is problematic owing to the singularity of the feasible set. We propose a perturbation strategy combining the relaxation of the equilibrium constraint with the restriction of the design domain to its regular part only. This strategy allows us to attack the problem numerically using standard non-linear programming algorithms. We rigorously study the optimality conditions for the original singular problem as well as the convergence of stationary points and globally optimal solutions to approximating problems towards respective stationary points and globally optimal solutions to the original problem. A limited numerical benchmarking of the algorithm is performed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Numerical derivation of contact mechanics interface laws using a finite element approach for large 3D deformationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2004Alex Alves Bandeira Abstract In this work a homogenization method is presented to obtain by numerical simulation interface laws for normal contact pressure based on statistical surface models. For this purpose and assuming elastic behaviour of the asperities, the interface law of Kragelsky et al. (Friction and Wear,Calculation Methods, Pergamon, 1982) is chosen for comparison. The non-penetration condition and interface models for contact that take into account the surface micro-structure are investigated in detail. A theoretical basis for the three-dimensional contact problem with finite deformations is shortly presented. The augmented Lagrangian method is then used to solve the contact problem with friction. The algorithms for frictional contact are derived based on a slip rule using backward Euler integration like in plasticity. Special attention was dedicated to the consistent derivation of the contact equations between finite element surfaces. A matrix formulation for a node-to-surface contact element is derived consisting of a master surface segment with four nodes and a contacting slave node. It was also necessary to consider the special cases of node-to-edge contact and node-to-node contact in order to achieve the desired asymptotic quadratic convergence in the Newton method. A numerical example is selected to show the ability of the contact formulation and the algorithm to represent interface law for rough surfaces. Copyright © 2003 John Wiley & Sons, Ltd. [source] Influence of polyethylene creep behavior on wear in total hip arthroplastyJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 3 2006Janaki R. Penmetsa Abstract After total hip arthroplasty (THA), polyethylene acetabular liner creep occurs quickly and serves to increases head,liner contact area and decrease contact pressures. What effect these early changes in contact mechanics will have on the wear behavior of the articulation remains unclear, and hence, selection or modification of polyethylene materials for optimal creep and wear performance is impossible. The objective of this study was to determine the influence of polyethylene creep behavior on volumetric wear and linear creep and wear penetration during simulated gait loading conditions. A finite element model of THA articulation was developed, and simultaneous numerical creep and wear simulation was performed to 10 million gait cycles with three levels of polyethylene creep behavior. Long-term volumetric wear and penetration were surprisingly unaffected by the polyethylene creep behavior due to the competing decrease in contact pressures coupled with increased contact area. In addition, variation in contact mechanics with the creep levels studied was only noteworthy in the initial postoperative period; after 1 million gait cycles, peak contact pressures and areas were within 13% regardless of the creep material behavior selected. Femoral head size had considerable impact on wear and penetration, while liner thickness primarily affected only early penetration. These results suggest that polyethylene creep behavior plays a major role in early penetration, but has little influence on the more important long-term volumetric wear. © 2005 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 24:422,427, 2006 [source] Friction evaluation of elastomers in lubricated contactLUBRICATION SCIENCE, Issue 10 2009Gregory F. Simmons Abstract Friction testing of elastomers in lubricated contact is discussed with a focus on developing experimental arrangements that can produce worthwhile results. Practical issues unique to elastomers are covered as well as their solutions, including contact mechanics, material response to loading, contact edges, oil absorption, cleaning and specimen geometry. A critique of reciprocating laboratory testing machines, including high-frequency short stroke and low-frequency long stroke friction and wear machines, is conducted for their usefulness, as is critical analysis of a wide variety of specimen configurations with the aim of helping the laboratory experimenter to overcome many of the pitfalls associated with testing of elastomers in lubricated conditions. Results from experiments using various testing arrangements are analysed, and it is found that the synthetic ester and mineral oil used produced similar results. Copyright © 2009 John Wiley & Sons, Ltd. [source] On the Use of the Nanoindentation Unloading Curve to Measure the Young's Modulus of Polymers on a Nanometer ScaleMACROMOLECULAR RAPID COMMUNICATIONS, Issue 22 2005Davide Tranchida Abstract Summary: The nanoindentation test is a fundamental tool to assess the link between morphology and mechanical properties. The preliminary results of a more exhaustive study about the applicability to polymers of the most used procedure to determine elastic modulus by indentation are reported in this short communication. A departure of the experimental conditions from the theoretical assumptions and results that give rise to the Oliver and Pharr analysis is shown to occur under a wide range of experimental conditions, with applied loads and penetration depths covering several orders of magnitude and using different indenter geometries. Unloading curves with exponents significantly larger than 2 are observed in disagreement with the contact mechanics approach used by Oliver and Pharr. An AFM image obtained in non contact mode of an indentation induced by a sharp AFM tip with a maximum applied load of ca 1.2 µN on amorphous PET. [source] The p-version of the FEM for computational contact mechanicsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008David Franke Contact analyses are being performed in various engineering applications. Here, like in most other fields, FE codes are based on low order elements using linear or quadratic shape functions. The intention of this paper is to show that finite elements with shape functions of high polynomial degree (p -FEM) are a very attractive alternative to low order elements, even for computational contact mechanics. One of the advantages is the possibility to enhance the element formulation with the blending function method in order to accurately discretize the given geometry, which leads in combination with high convergence rates to very efficient computations. In order to solve the problem of frictionless contact, a penalty formulation is applied in this work. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||