Laurent Duchêne

University of Liège, Luik, Walloon Region, Belgium

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Publications (50)21.35 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: This article presents an analytic model for the prediction of wrinkling occurring in metal/polymer coatings under particular conditions. Owing to different thermal expansion coefficients (TECs) of the substrate and the different coating layers, temperature variation can induce a compressive stress in the coating. The wrinkling is the material response to the instability caused by this compressive stress. In this study, a reference case was selected: a 0.27-mm-thick steel sheet with a 5-μm-thick polymer layer and, on top of it, a thin aluminum film of 50 nm in thickness. For this reference case, it was observed and predicted by the model that an increase in temperature yielded to the wrinkling of the thin aluminum film. The geometry of the multilayer coating and the properties of the constituent materials are factors able to promote or prevent the wrinkle. To better understand and predict their effects, a sensitivity analysis was carried out with the proposed analytic model. A special attention was devoted to the temperature when wrinkling occurs. The key parameters having a significant influence on the wrinkling temperature were identified. It is concluded that the elastic modulus of the thin aluminum film and that of the polymer, the TEC of the thin film, and the initial stress induced during the processing of the multilayer system all had a significant influence on the wrinkling temperature.
    Journal of Materials Engineering and Performance 09/2013; · 0.92 Impact Factor
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    ABSTRACT: This paper presents an experimental study of the quasi-static mechanical behavior of TA6V titanium alloy. Different monotonic tests were carried out in several orientations in the plane of the sheet in order to characterize the anisotropy and the tension-compression asymmetry exhibited by the material. Initial yielding is modeled by the phenomenological CPB06 criterion and Voce's isotropic hardening is used to describe its evolution. The simulation of a deep-drawing process is performed using the proposed constitutive modeling and compared with experimental data.
    05/2013;
  • Proceedings of the 12th World Conference on Titanium; 10/2012
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    ABSTRACT: The miniaturization of metallic samples has been proved to deeply affect their mechanical properties leading to a softening or a hardening effect depending on the order of the dimension reduction. The objective of this work is to provide new numerical results which explain the softening mechanisms on the mechanical behavior for nickel polycrystals which have been experimentally characterized by the authors in a previous published paper (Keller et al., 2011). Based on a strain gradient crystalline plasticity model identified for nickel, simulations of tensile tests were performed for samples with different thicknesses and grain sizes. The simulations correctly reproduce the softening effect linked to a decrease in the thickness and in the number of grains across the thickness. The analysis of the plasticity mechanisms shows that the softening is due to surface effects which are discussed in terms of grain orientations, dislocation mean free path and long-range back-stress. The model also predicts a hardening mechanism for further dimension reduction if the samples have only grain boundaries perpendicular to the tensile direction. In this case, the modification of the mechanical behavior is due to strain gradients formation.
    International Journal of Plasticity 01/2012; 29:155–172. · 4.36 Impact Factor
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    ABSTRACT: We present in this paper a new eight node solid‐shell finite element called SSH3D (Three Dimensional Solid‐Shell). This element is currently implemented in the frame of the in‐house research code called LAGAMINE. Here the Enhanced Assumed Strain (EAS) technique based on the Hu‐Washizu variational principle, described in [1] and [2], is used to cure the volumetric locking occurring when the material shows nearly incompressible behavior and Poisson’s thickness locking caused by the high aspect ratio of the finite element. In the proposed element, the EAS technique can be combined with the Assumed Natural Strain (ANS) [3–5] concept to treat shear locking caused by the transverse shear strain and curvature thickness locking caused by the transverse normal strain. Different schemes for the ANS concept are implemented while the number of integration points and the number of EAS modes are element parameters (the element uses four integration points in the plane of the element and at least two integration points through the thickness direction in a single element layer). These features must be adjusted by the user according to the studied process (geometry and loading) so as to avoid locking and limit the calculation time. This element was successfully tested and the numerical remedies were verified using several kinds of patch tests. A double sided contact problem is modeled in order to investigate the performance and accuracy of the developed element and to validate the suggested approach.
    AIP Conference Proceedings. 08/2011; 1383(1):374-381.
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    ABSTRACT: This paper presents an experimental and theoretical study of the quasi-static behavior of TA6V titanium alloy in plane strain state. In order to quantify the anisotropy of the material, tests were carried out at room temperature on specimens cut out from a sheet along three loading directions. The initial yield locus is described by the phenomenological CPB06ex3 criterion and Voce's type isotropic hardening is used. Finite element simulations are performed and compared with the experiments.
    08/2011;
  • Proceedings of the 12th World Conference on Titanium. 06/2011;
  • International Journal for Numerical Methods in Engineering 02/2011; 85(8):1049-1072. · 2.06 Impact Factor
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    ABSTRACT: This article focuses on the numerical modeling of nanoindentation tests performed on the hexagonal α phase of Ti-5553 alloy in order to identify its mechanical behavior. The main goal consists in determining the relative strength of the slip modes in the α phase of Ti-5553. This work was performed using an elastoviscoplastic crystal plasticity-based constitutive law. The difficulties in determining the slip systems that can be activated and their corresponding critical resolved shear stresses (CRSS) are discussed. Numerical predictions are compared to experimental nanoindentation curves.
    European Journal of Mechanics A-solids - EUR J MECH A-SOLID. 01/2011; 30(3):248-255.
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    ABSTRACT: A recently developed AlMgSc alloy is studied since this material, which is well adapted to the aeronautic domain, is poorly known.The first objective is to reach a better knowledge of this alloy to provide the missing useful information to the aeronautic industry and to help research institutes who want to simulate sheet forming processes by Finite Element (FE) simulations. A set of experimental tests has been performed on the as-received sheets, material laws have been chosen and the corresponding material parameters have been adjusted to correctly describe the material behaviour.The second objective is to study the applicability of the Single Point Incremental Forming process (SPIF) on this material. Truncated cones with different geometries were formed and the maximum forming angle was determined. A numerical model was developed and proved to be able to predict both the force evolution during the process and the final geometrical shape. Moreover, the model helps reaching a better understanding of the process.The characterisation method described in this research and applied on the AlMgSc alloy can be extended to other alloys. In addition, the numerical simplified model, able to accurately describe the SPIF process with a reduced computation time, can be used to study more complex geometries.
    Journal of Materials Processing Technology - J MATER PROCESS TECHNOL. 01/2011; 211(11):1684-1693.
  • 01/2011: pages 157-179;
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    ABSTRACT: The paper presents an experimental study of the quasi-static deformation behavior of a TA-6 V in sheet form. To quantify the plastic anisotropy and the tension–compression asymmetry of this material at room temperature, monotonic tensile and compressive tests were carried out on specimens cut out along several orientations in the plane of the sheet. It was observed that although the tensile flow stress anisotropy is very mild, the Lankford coefficients’ anisotropy is very pronounced. To describe the observed mechanical response an elastic/plastic approach was used. Yielding was described using a family of yield criteria that account for strength differential effects and allow an improved description of the anisotropy and its evolution through multiple linear transformations. Comparisons between uniaxial monotonic data and FE simulations using the model show a very good agreement.
    International Journal of Solids and Structures 01/2011; 48(9):1277-1289. · 1.87 Impact Factor
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    ABSTRACT: In order to couple the damage evolution and the stress state of DP steel grades, a new advanced GTN (Gurson–Tvergaard–Needleman) model was developed and implemented into a finite element code. This model is an extension of the original one. It takes into account the plastic anisotropy and the mixed (isotropic + kinematic) hardening of the matrix. Two different methods to compute the void volume fraction were developed and used within the constitutive equations. The first method is new and allows the accurate modeling of the observations of damage initiation and growth in DP steels measured using high-resolution X-ray absorption tomography ( and ). The second method is classic and assumes the additive decomposition of the total void volume fraction into a nucleation and a growth part. A parametric study is carried out to assess the effect of the kinematic hardening on some mechanical parameters such as the equivalent plastic strain, the triaxiality and the porosity. The numerical predictions are favorably compared to the experimental results.
    Mechanics of Materials. 01/2011; 43(3):139-156.
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    ABSTRACT: The strain rate dependence of plastic yield and failure properties displayed by most metals affects energies, forces and forming limits involved in high speed forming processes. This paper investigates the influence of the strain rate on the forming properties of one laboratory made and three commercial steel grades: a CMnAl TRIP steel, the ferritic structural steel S235JR, the drawing steel DC04 and the ferritic stainless steel AISI 409. First, split Hopkinson tensile bar (SHTB) experiments are carried out to assess the influence of the strain rate on the materials’ stress–strain curves. Subsequently, the obtained SHTB results, together with static tensile test results, are used to model the constitutive behaviour of the investigated steels using the phenomenological Johnson–Cook (JC) model and the Voce model, thus allowing dynamic modelling of forming processes. Finally, forming limit diagrams (FLDs) are calculated using the Marciniak–Kuczynski method. The results clearly show that the effect of the strain rate on forces and energies involved in a forming process, and the forming limits is non-negligible and strongly material dependent.
    Journal of Materials Processing Technology 01/2011; 211(8):1457-1464. · 1.95 Impact Factor
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    ABSTRACT: In the first part of this paper, the theoretical aspects and the algorithmic developments related to the construction of the PBST (Pure Bending Simulation Tool) were provided. In this second part, this tool is used to simulate the pure bending process. The sensitivity of the bendability prediction to certain mechanical properties and phenomena (such as initial porosity and hardening parameters) is investigated by means of a parametric study. The efficiency and the performance of this tool (in terms of accuracy and computation time) compared to the FE method are shown through various numerical simulations.
    Materials Science and Engineering: A. 11/2010; 528(1):442–448.
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    ABSTRACT: This paper deals with the pure bending of thin and thick metallic sheets under plane strain condition. Its main objective is to construct an efficient, robust, incremental numerical tool that can be used to simulate the bending process and predict the sheets’ bendability. In this investigation, the material constitutive law describing the mechanical behavior of the sheet is defined by an extended Gurson model. This model generalizes Gurson's original one to account for both plastic anisotropy and mixed (isotropic and kinematic) hardening of the matrix. In this model, only the growth phase of voids was considered (without taking into account nucleation). Here, the extended model was coupled with the kinematics of the pure bending process and with the equilibrium equations, and then implemented in an incremental numerical tool in order to predict the bendability of the sheets studied. This bendability was then verified using two different criteria. Part I of this paper focuses on the constitutive law, fulfillment of the force equilibrium, the thickness evolution and the shift of the neutral fiber, together with a comparison and discussion of the choices made by other authors regarding these parameters. The validation of the model developed in this paper will be carried out in Part II through simulations of the pure bending process.
    Materials Science and Engineering: A. 11/2010; 528(1):434–441.
  • Steel Research International 01/2010; 81(9):1173-1176. · 0.49 Impact Factor
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    ABSTRACT: In this paper, the forming behavior of nickel sheets is investigated as a function of the number of grains across the thickness by finite element simulations. Experimental tensile tests were carried out on nickel samples of approximately 100 μm grain size and thicknesses ranging between 12.5 μm and 3.2 mm. The decrease of the number of grains across the thickness involves a decrease of tensile stress due to the apparition of surface effects. These latter were taken into account for the deep drawing simulation of samples with 250 μm thickness by the use of two different constitutive elasto-plastic laws for surface and core grains. The simulations with two laws predict a modification of the distribution of the V.M. equivalent stress and of the damage zones compared to results from simulations using a simple average law.
    AIP Conference Proceedings 01/2010; 1252:1025-1030.
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    ABSTRACT: The advances achieved in phenomenological constitutive laws and their implementation in finite element codes for predicting material behavior during forming processes have motivated the research on material identification parameters in order to ensure prediction accuracy. New models require experimental points describing a bi-axial stress state for proper calibration, and the features of the plane strain tensile test have made it one of the most used. The test's principal inconvenience is the influence of the free edges on strain field homogeneity and stress computation.Experimental measurements of the strain field over the gauge zone on a plane strain tensile test specimen during deformation reveals the evolution of the size of the specimen area that represents a plane strain state.This article proposes a methodology, based on a numerical analysis of a plane strain tensile test for different materials and specimen geometry, to experimentally identify the evolution of the homogeneous strain field zone during deformation. This research defines an expression for computation of the actual stress in the specimen's plane strain state zone along the loading direction using experimental data and including the edge effect evolution in terms of plastic strain.The influence of the specimen's geometry and material anisotropy over the stress computation error is discussed and quantified. The stress computation expression proposed here can be adapted to other specimen geometries.
    Journal of Materials Processing Technology - J MATER PROCESS TECHNOL. 01/2010; 210(13):1772-1779.
  • Materials Science Forum - MATER SCI FORUM. 01/2010;

Publication Stats

123 Citations
46 Downloads
2k Views
21.35 Total Impact Points

Institutions

  • 2002–2013
    • University of Liège
      • Materials and Structures Mechanics Laboratory (M&S)
      Luik, Walloon Region, Belgium
  • 2010
    • Fonds de la Recherche Scientifique (FNRS)
      Bruxelles, Brussels Capital Region, Belgium
  • 2005–2007
    • Royal Military Academy
      Bruxelles, Brussels Capital Region, Belgium