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Noel O.,University of Maine, France | Mazeran P.-E.,CNRS Roberval Laboratory (Mechanical Research Unit) | Nasrallah H.,University of Maine, France
Physical Review Letters | Year: 2012

The influence of sliding velocity on the adhesion force in a nanometer-sized contact was investigated with a novel atomic force microscope experimental setup that allows measuring adhesion forces while the probe is sliding at continuous and constant velocities. For hydrophobic surfaces, the adhesion forces (mainly van der Waals forces) remain constant, whereas for hydrophilic surfaces, adhesion forces (mainly capillary forces) decrease linearly with a logarithmic increase of the sliding velocity. The experimental data are well explained by a model based on a thermally activated growth process of a capillary meniscus. © 2012 American Physical Society.

Chazot J.-D.,CNRS Roberval Laboratory (Mechanical Research Unit) | Nennig B.,Laboratoire dIngenierie des Systemes Mecaniques et des MAteriaux | Perrey-Debain E.,CNRS Roberval Laboratory (Mechanical Research Unit)
Journal of Sound and Vibration | Year: 2013

The paper deals with the numerical simulation of the acoustic field in two-dimensional cavities in which absorbing materials are present. Though Finite Element Method (FEM) could be employed for this purpose, the discretization level required for achieving reasonable accuracy renders the method impractical in the mid-frequency range. To alleviate this limitation, the Partition of Unity Finite Element Method (PUFEM) using plane wave functions has been shown to be very effective for solving short wave Helmholtz problems. In the present work, the method is extended to the computation of the pressure wave field within the absorbing media which is modeled as a bulk-reacting material characterized by a complex-valued and frequency dependent mean density and dynamic compressibility. Lagrange multipliers are used to enforce the transmission conditions at the air-material interface. Performances of the PUFEM are compared with a standard FEM in several examples of practical interests. It is shown that the technique is a good candidate for solving noise control problems at high frequency. © 2012 Elsevier Ltd. All rights reserved.

Zhang E.L.,CNRS Roberval Laboratory (Mechanical Research Unit) | Feissel P.,CNRS Roberval Laboratory (Mechanical Research Unit) | Antoni J.,CNRS Roberval Laboratory (Mechanical Research Unit)
Probabilistic Engineering Mechanics | Year: 2011

This paper presents a comprehensive Bayesian approach for structural model updating which accounts for errors of different kinds, including measurement noise, nonlinear distortions stemming from the linearization of the model, and modeling errors due to the limited predictability of the latter. In particular, this allows the computation of any type of statistics on the updated parameters, such as joint or marginal probability density functions, or confidence intervals. The present work includes four main contributions that make the Bayesian updating approach feasible with general numerical models: (1) the proposal of a specific experimental protocol based on multisine excitations to accurately assess measurement errors in the frequency domain; (2) two possible strategies to represent the modeling error as additional random variables to be inferred jointly with the model parameters; (3) the introduction of a polynomial chaos expansion that provides a surrogate mapping between the probability spaces of the prior random variables and the model modal parameters; (4) the use of an evolutionary Monte Carlo Markov Chain which, in conjunction with the polynomial chaos expansion, can sample the posterior probability density function of the updated parameters at a very reasonable cost. The proposed approach is validated by numerical and experimental examples. © 2011 Elsevier Ltd. All rights reserved.

Simard P.,CNRS Roberval Laboratory (Mechanical Research Unit) | Antoni J.,INSA Lyon
Applied Acoustics | Year: 2013

This work experiments and investigates the problem of acoustic sources identification from a limited number of measurements delivered by a microphone array as a Basis Pursuit problem. The basic idea beyond Basis Pursuit is to search for a solution that minimizes the ℓ1 norm of the solution rather than the usual sum of squares (ℓ2 norm) of the residual error. Basis Pursuit has been developed in the context of Compressed Sensing (CS), and has already proved to be efficient in a great number of applications. However, the quality of the obtained results is subdued to restricted conditions whose fulfillment in acoustics are investigated in this paper depending on geometrical parameters such as the source/array distance or the array aperture. This leads to the proposition of several practical guidelines for the experimenter as how to select a microphone array and how to optimaly position it w.r.t the radiating source of interest. Simulations and experimental data are used to demonstrate the relevance and limitations of this approach. The results proved to be better than those obtained by conventional Beamforming (BF), even in its near-field focusing version based on spherical waves. © 2013 Elsevier Ltd. All rights reserved.

Xia L.,CNRS Roberval Laboratory (Mechanical Research Unit) | Breitkopf P.,CNRS Roberval Laboratory (Mechanical Research Unit)
Archives of Computational Methods in Engineering | Year: 2016

Research on topology optimization mainly deals with the design of monoscale structures, which are usually made of homogeneous materials. Recent advances of multiscale structural modeling enables the consideration of microscale material heterogeneities and constituent nonlinearities when assessing the macroscale structural performance. However, due to the modeling complexity and the expensive computing requirement of multiscale modeling, there has been very limited research on topology optimization of multiscale nonlinear structures. This paper reviews firstly recent advances made by the authors on topology optimization of multiscale nonlinear structures, in particular techniques regarding to nonlinear topology optimization and computational homogenization (also known as FE2) are summarized. Then the conventional concurrent material and structure topology optimization design approaches are reviewed and compared with a recently proposed FE2-based design approach, which treats the microscale topology optimization process integrally as a generalized nonlinear constitutive behavior. In addition, discussions on the use of model reduction techniques is provided in regard to the prohibitive computational cost. © 2016 CIMNE, Barcelona, Spain

Jourani A.,CNRS Roberval Laboratory (Mechanical Research Unit)
International Journal of Surface Science and Engineering | Year: 2015

This study focuses on the belt finishing process to understand the effect of the local geometry of each abrasive grain via the curvature radius and the attack angle on the local contact temperature. In order to reach this last parameter, a three-dimensional numerical model is established and presented in order to determine the temperature distribution at the interface abrasive papers/workpiece. The established model considers that the local geometry of each abrasive grain is conical with a hemispherical tip. The numerical results show that at a small depth of penetration, both sphere and cone have an influence on temperatures distribution. For larger depths, this distribution depends only on the conical geometry of the abrasive grains. It is also shown that the effect of the interaction of asperities on the temperature during belt finishing cannot be neglected, especially at higher load. Copyright © 2015 Inderscience Enterprises Ltd.

Jourani A.,CNRS Roberval Laboratory (Mechanical Research Unit)
International Journal of Materials and Product Technology | Year: 2015

In this work, we study the influence of roughness geometries on the contact force, contact area and pressure distribution during a static contact between a rough surface and a smooth rigid plane by using two elastic geometrical models. The first one is spherical where each asperity can be characterised by the height and the radius of curvature. The second approach is a conical where the rough contact is modelled by cones. In order to discuss the validity of these two geometrical models, they are compared with a numerical solution of the Boussinesq equation which does not take into account the local geometry of the asperities. The results show clearly that the conical model allows having more realistic values of the contact parameters and model correctly the elastic rough contact. However, the spherical approach of the asperities overestimates the pressures undergone by the asperities. Copyright © 2015 Inderscience Enterprises Ltd.

Xia L.,CNRS Roberval Laboratory (Mechanical Research Unit) | Breitkopf P.,CNRS Roberval Laboratory (Mechanical Research Unit)
Computer Methods in Applied Mechanics and Engineering | Year: 2014

This paper presents a reduced multiscale model for macroscopic structural design considering microscopic material nonlinear microstructures. This work introduces Reduced Order Model (ROM) to alleviate the heavy computational demand of nonlinear nested multiscale procedures, particularly in an optimization framework which requires multiple loops involving similar computations. The surrogate model constructed using Proper Orthogonal Decomposition (POD) and Diffuse Approximation reduces the computational effort for solving the microscopic boundary value problems. Multiscale analysis model (FE2) is applied to link structure and microstructures in the two scales. Maximum stiffness design of the macroscopic structure is realized using a discrete level-set topology optimization model. It is shown by means of numerical tests that the reduced multiscale model provides reasonable designs as compared to those obtained by the unreduced model while with a significantly reduced computational effort. © 2014 Elsevier B.V.

Anselme K.,CNRS Mulhouse Institute of Materials Science | Bigerelle M.,CNRS Roberval Laboratory (Mechanical Research Unit)
International Materials Reviews | Year: 2011

Many approaches are used to modify the surface topography of implant materials. Some produce unordered surfaces using, for example, classical implant surface treatments, whereas others produce ordered surfaces by micro- and nanopatterning techniques. Surface topographies can be characterised by several methods that can acquire two-dimensional profiles or three-dimensional measurements and calculate different roughness parameters. The importance of using systematically several roughness parameters for correlation with biological response, and of consider these parameters at different scales will be demonstrated. Furthermore, it will be described, from a general point of view, how cells are able to identify and respond to surface topography. The role of membrane receptors, cytoskeleton, filopods and intracellular signal transduction in the response to topography will be considered and discussed. A critical review of more than 300 papers provides the basis for illustrating how mammalian cells respond to surface topography and how their rugophilia, the increased cell response to rougher surfaces, is a function of cell phenotype. For the first time, the rugophilia of cells from different tissue origins is compared in a synthetic table. © 2011 Institute of Materials, Minerals and Mining and ASM International.

Xia L.,CNRS Roberval Laboratory (Mechanical Research Unit) | Breitkopf P.,CNRS Roberval Laboratory (Mechanical Research Unit)
Computer Methods in Applied Mechanics and Engineering | Year: 2014

This paper revisits concurrent design of material and structure within FE2 nonlinear multiscale analysis framework. For structural stiffness maximization at macroscopic scale, design variables are defined at the both scales. Cellular material models are defined at microscopic scale in a pointwise manner for the considered macroscopic structure. They are optimized to adapt the macroscopic structural physical response. Though linear models are assumed at both scales, the macroscopic structural equilibrium is in general nonlinear due to the adaptation of cellular material microstructures. For this reason, an iterative resolution based on FE2 scheme is developed to address this nonlinearity. Discrete topology optimization algorithm, bi-directional evolutionary structural optimization (BESO) is used at the both scales. It is shown by means of numerical tests that FE2 scheme can well bridge the two scales and address the nonlinearity. Reasonable design solutions of the macroscopic structure and its corresponding cellular materials have been obtained by the developed concurrent design framework. © 2014 Elsevier B.V.

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