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See detailThermal history modelling to understand microstructures observed in repair technology of Ti-6Al-4V
Tran, Hoang Son ULg; Tchuindjang, Jérôme Tchoufack ULg; Hakan, Paydas et al

in Extended Abstract book of 14th Conf. on Computer Methods in Materials Technology KomPlasTech 2017 (2017, January)

Laser cladding is a metal deposition technique used to fabricate or repair components. In the present work Ti-6Al-4V deposits with a variable thickness are studied to assess the use of laser cladding as a ... [more ▼]

Laser cladding is a metal deposition technique used to fabricate or repair components. In the present work Ti-6Al-4V deposits with a variable thickness are studied to assess the use of laser cladding as a repair technology [1]. Solidification following melting and partial remelting of pre-existing layers is coupled with heat treatment of the solidified material due to the repeated heating and cooling cycles during building. The effect of the building strategy on the metallurgical characteristics of the material for a decreasing track length (DTL) or a constant track length (CTL) strategy is analyzed. Depending on the possible heat accumulation, the nature of the phases are determined by metallography and hardness maps of the deposits. Optical Microscopy (OM), Stereo Microscopy (SM), and Scanning Electron Microscopy (SEM) were used in order to study the microstructure. The generation of the microstructure results from the material thermal history. This one is computed by Finite Element Method and a careful analysis establishes the link between the phase state and the detailed thermal history. [less ▲]

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See detailLaser Cladding Finite Element Modelling Application to Ti6Al4V,
Tran, Hoang Son ULg; Brusten, Romain; Jardin, Ruben et al

Conference (2016, November 03)

Corrélation entre les champs thermiques prédits et la microstructure observée.

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See detailQuasicontinuum analysis of interaction between screw dislocation and coherent twin boundary
Tran, Hoang Son ULg; Duchene, Laurent ULg; Tummala, Hareesh et al

Conference (2016, September 07)

The interaction between pure screw dislocation with dislocation line directions lying parallel to the twin plane and Coherent Twin Boundary Σ3 of copper has been studied using Quasi-Continuum method. The ... [more ▼]

The interaction between pure screw dislocation with dislocation line directions lying parallel to the twin plane and Coherent Twin Boundary Σ3 of copper has been studied using Quasi-Continuum method. The coherent twin boundary provides high barrier to slip transmission. The dislocation pile-up modifies the stress field at its intersection with the grain boundary. We introduce a methodology to calculate the stress barriers during slip–GB interaction. Screw dislocation approaching the boundary from one side may either propagate into the adjacent twin grain by cutting through the twin boundary. Quantitative estimation of critical stress for transmission phenomena is performed by using virial stress. The mechanism and critical stress obtained were in line with the literature. Such information can be used as input for Discrete Dislocation Dynamics models [less ▲]

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See detailModeling the ductile fracture and the plastic anisotropy of DC01 steel at room temperature and low strain rates
Tuninetti, Victor; Yuan, Sibo ULg; Gilles, Gaëtan et al

Scientific conference (2016, September)

This paper presents different extensions of the classical GTN damage model implemented in a finite element code. The goal of this study is to assess these extensions for the numerical prediction of ... [more ▼]

This paper presents different extensions of the classical GTN damage model implemented in a finite element code. The goal of this study is to assess these extensions for the numerical prediction of failure of a DC01 steel sheet during a single point incremental forming process, after a proper identification of the material parameters. It is shown that the prediction of failure appears too early compared to experimental results. Though, the use of the Thomason criterion permitted to delay the onset of coalescence and consequently the final failure. [less ▲]

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See detail2D and 3D FE models of laser cladding process
Jardin, Ruben; Hoang, Son Tran; Hashemi, Seyedeh Neda ULg et al

in Booklet of the conference with extended abstract and short paper of less than 6 pages (2016, July)

Lien entre le champ thermique 2D et 3D calculé pour un cas de laser cladding d acier au chrome

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See detailSafe, flexible and efficient sheet metal forming: formability - fracture, incremental sheet forming & rolling
Banabic, Dorel; Habraken, Anne ULg; Yoon, Jeong Whan

in International Journal of Material Forming (2016), 9(3),

Editorial of the thematic issue

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See detailSimulation of a two-slope pyramid made by SPIF using an adaptive remeshing method with solid-shell finite element
Velosa De Sena, José ULg; Guzmán Inostroza, Carlos Felipe ULg; Duchene, Laurent ULg et al

in International Journal of Material Forming (2016), 9(3), 259-434

Single point incremental forming (SPIF) is an emerging application in sheet metal prototyping and small batch production, which enables dieless production of sheet metal parts. This research area has ... [more ▼]

Single point incremental forming (SPIF) is an emerging application in sheet metal prototyping and small batch production, which enables dieless production of sheet metal parts. This research area has grown in the last years, both experimentally and numerically. However, numerical investigations into SPIF process need further improvement to predict the formed shape correctly and faster than current approaches. The current work aims the use of an adaptive remeshing technique, originally developed for shell and later extended to 3D “brick” elements, leading to a Reduced Enhanced Solid-Shell formulation. The CPU time reduction is a demanded request to perform the numerical simulations. A two-slope pyramid shape is used to carry out the numerical simulation and modelling. Its geometric difficulty on the numerical shape prediction and the through thickness stress behaviour are the main analysis targets in the present work. This work confirmed a significant CPU time reduction and an acceptable shape prediction accuracy using an adaptive remeshing method combined with the selected solid-shell element. The stress distribution in thickness direction revealed the occurrence of bending/unbending plus stretching and plastic deformation in regions far from the local deformation in the tool vicinity. [less ▲]

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See detailSingle point incremental forming simulation with adaptive remeshing technique using solid-shell elements
Sena, José; Lequesne, Cedric; Duchene, Laurent ULg et al

in Engineering Computations International Journal for Computer- Aided Engineering and Software (2016), 33(5), 1388-1421

Numerical simulation of the single point incremental forming (SPIF) processes can be very demanding and time consuming due to the constantly changing contact conditions between the tool and the sheet ... [more ▼]

Numerical simulation of the single point incremental forming (SPIF) processes can be very demanding and time consuming due to the constantly changing contact conditions between the tool and the sheet surface, as well as the nonlinear material behaviour combined with non-monotonic strain paths. The purpose of this paper is to propose an adaptive remeshing technique implemented in the in-house implicit finite element code LAGAMINE, to reduce the simulation time. This remeshing technique automatically refines only a portion of the sheet mesh in vicinity of the tool, therefore following the tool motion. As a result, refined meshes are avoided and consequently the total CPU time can be drastically reduced. [less ▲]

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See detailNumerical Simulations of a Two Roll Round Bar Straightener
Flipon, Baptiste; Lawrjaniec, Didier; Papeleux, Luc ULg et al

in AIP Conference Proceedings 1769, 120001 (2016); (2016, April 28)

A 2-roll bar straightener is a finishing process applied after the rolling operation of round steel bars. During the straightening, the bar rotation is induced by the two rotating rolls. It also undergoes ... [more ▼]

A 2-roll bar straightener is a finishing process applied after the rolling operation of round steel bars. During the straightening, the bar rotation is induced by the two rotating rolls. It also undergoes an alternate bending in such a way that the bar section is finally deformed uniformly. The purpose of this process is to correct the curvature defaults of the rolled bar. Indeed, the bar must be straight before being sent to the client and a straightened uniform surface layer is appreciated. With the apparition of new grades and also new diameters of steel round bars, it becomes essential to better understand the straightening process in order to (i) have a better knowledge of what the round bar undergoes during the process, (ii) precisely understand the straightening process, the effect of each component and the process parameters. [less ▲]

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See detailAbout the Enhanced Formability of Single Point Incremental Forming
Habraken, Anne ULg; Guzmán Inostroza, Carlos Felipe ULg

Scientific conference (2016, February 09)

Analysis of the formability in Single Point Incremental Forming Process: deformation mechanism, link witth Forming Limit Curves and damage approach, bad prediction of Gurson model for DC01 steel.

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See detailLocal thermal history during the laser additive manufacturing of steel
Mertens, Anne ULg; Hashemi, Seyedeh Neda ULg; Tchuindjang, Jérôme Tchoufack ULg et al

Conference (2016, February 09)

Laser additive manufacturing techniques – such as laser cladding − were developed in the late 1990s as economic layer-by-layer near-net-shape processes allowing for the production or restoration of ... [more ▼]

Laser additive manufacturing techniques – such as laser cladding − were developed in the late 1990s as economic layer-by-layer near-net-shape processes allowing for the production or restoration of complex metallic parts. These techniques are characterised by ultra-fast solidification and cooling rates, thus giving rise to ultra-fine out-of-equilibrium microstructures with potentially enhanced mechanical properties. However, the general quality of a component, as well as its dimensional accuracy, microstructure and final usage properties are strongly influenced by the local thermal history experienced during fabrication. As a consequence, a deeper understanding of the influence of the various processing parameters on the local thermal history during fabrication is of paramount importance, and it can only be reached by combining detailed experimental studies and modeling. Keeping this in mind, the present paper reviews on-going investigations carried out in the Metallic Materials Science Unit of the University of Liege in the laser additive manufacturing of HSS and of stainless steel 316L. [less ▲]

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See detailComparison of residual stresses on long rolled profiles measured by X-ray diffraction, ring core and the sectioning methods and simulated by FE method
Bouffioux, Chantal ULg; Pesci, Raphaël; Boman, Romain ULg et al

in Thin-Walled Structures (2016), 104

Sheet piles are produced by hot rolling, a cooling step and, if required, by a straightening operation. Numerical simulations indicate that the stress field is almost homogeneous through the thickness ... [more ▼]

Sheet piles are produced by hot rolling, a cooling step and, if required, by a straightening operation. Numerical simulations indicate that the stress field is almost homogeneous through the thickness, justifying the comparison of X-ray diffraction, ring core and the sectioning methods applied after the cooling step and after the straightening process. The equipment, the steps of the experimental procedures and the results are detailed, showing the limits, the specificities and the advantages of each method. Moreover, the amplitude and the distribution of the stresses along the width of the sections present good agreement with results of numerical simulations. [less ▲]

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See detailOn the comparison of two solid-shell formulations based on in-plane reduced and full integration schemes in linear and non-linear applications
ben bettaieb, Amine; Velosa de Sena, J.I.; Alves de Sousa, Ricardo et al

in Finite Elements in Analysis and Design (2015), 107

In the present paper, a detailed description of the formulation of the new SSH3D solid-shell element is presented. This formulation is compared with the previously proposed RESS solid-shell element [1, 2 ... [more ▼]

In the present paper, a detailed description of the formulation of the new SSH3D solid-shell element is presented. This formulation is compared with the previously proposed RESS solid-shell element [1, 2]. Both elements were recently implemented within the LAGAMINE in-house research finite element code. These solid-shell elements possess eight nodes with only displacement nodal degrees of freedom (DOF). In order to overcome various locking pathologies, the SSH3D formulation employs the well known Enhanced Assumed Strain (EAS) concept originally introduced by Simo and Rifai [3] and based on the Hu-Veubeke-Washizu variational principle combined with the Assumed Natural Strain (ANS) technique based on the work of Dvorkin and Bathe [4]. For the RESS solid-shell element, on the other hand, only the EAS technique is used with a Reduced Integration (RI) Scheme. A particular characteristic of these elements is their special integration schemes, with an arbitrary number of integration points along the thickness direction, dedicated to analyze problems involving non-linear through-thickness distribution (i.e. metal forming applications) without requiring many element layers. The formulation of the SSH3D element is also particular, with regard to the solid-shell elements proposed in the literature, in the sense that it is characterized by an in-plane full integration and a large variety in terms of (i) enhancing parameters, (ii) the ANS version choice and (iii) the number of integration points through the thickness direction. The choice for these three parameters should be adapted to each problem so as to obtain accurate results and to keep the calculation time low. Numerous numerical examples are performed to investigate the performance of these elements. These examples illustrate the reliability and the efficiency of the proposed formulations in various cases including linear and non-linear problems. SSH3D element is more robust thanks to the various options proposed and its full in-plane integration scheme, while RESS element in more efficient from a computational point of view. [less ▲]

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See detailFE modeling of the cooling and tempering steps of bimetallic rolling mill rolls
Neira Torres, Ingrid; Gilles, Gaëtan ULg; Tchuindjang, Jérôme Tchoufack ULg et al

in International Journal of Material Forming (2015)

Numerical simulations enable the analysis of the stress and strain histories of bimetallic rolling mill rolls. The history of rolling mill rolls is simulated by thermo-mechanical metallurgical finite ... [more ▼]

Numerical simulations enable the analysis of the stress and strain histories of bimetallic rolling mill rolls. The history of rolling mill rolls is simulated by thermo-mechanical metallurgical finite element code while considering two steps: post-casting cooling and subsequent tempering heat treatment. The model requires a notably large set of material parameters. For different phases and temperatures, Young modulus, yield limit and tangent plastic modulus are determined through compression tests. Rupture stresses and strains are obtained by tensile tests. Thermo-physical parameters are measured by such experimental methods as dilatometry, DSC (Differential Scanning Calorimetry) and Laser Flash methods. Such parameters as the transformation plasticity coefiicients for the ferrite, pearlite and martensite phases are identified through an inverse method. From the simulation results, the profile of the stresses evolution at different critical times is presented. An analysis of the potential damage is proposed by comparing the predicted axial stress \vith rupture stresses. The perspective of the Ghosh and McClintock damage criteria is also investigated. [less ▲]

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See detail2D Thermal model of powder injection laser cladding of high speed steels (HSS)
Hashemi, Seyedeh Neda ULg; Gilles, Gatën; Tomé Jardin, Ruben Antonio ULg et al

Conference (2015, October 23)

A two-dimensional multi-layer model for the transient temperature field analysis of Laser cladding process is developed. This model allows studying the thermal field of the multilayer deposits during ... [more ▼]

A two-dimensional multi-layer model for the transient temperature field analysis of Laser cladding process is developed. This model allows studying the thermal field of the multilayer deposits during their development by laser, and the "flat" substrate on which the deposition is carried. [less ▲]

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See detailInteraction between dislocation and coherent twin boundary by quasicontinuum model
Hoang, Son Tran; Tummala, Hareesh; Duchene, Laurent ULg et al

in Proceedings of XIII International Conference on Computational Plasticity. Fundamentals and Applications COMPLAS ebook open accesss XIII (2015, September 02)

methodAbstract.The interaction between lattice dislocations and Coherent Twin Boundary Σ3 {111} of copper has been studied using Quasi-Continuum method. The coherent twin boundary provides high barrier to ... [more ▼]

methodAbstract.The interaction between lattice dislocations and Coherent Twin Boundary Σ3 {111} of copper has been studied using Quasi-Continuum method. The coherent twin boundary provides high barrier to slip transmission. The dislocation pile-up modifies the stress field at its intersection with the grain boundary. A different reaction process compared with the case of single dislocations is noticed. One observes the nucleation of a Lomer-type dislocation with Burgers vector of ½ <110 > and its glide onthe (100) cube plane in the adjacent grain. This phenomenon has been observed with Transmission Electron Microscopy at room temperature and in other Molecular Dynamics simulations. We also show a novel interaction mechanism between Lomer-type dislocation and Coherent Twin Boundary. This interactionprocess leaves a dislocation with a Burgers vector coincident with the complete lattice shift of the Coherent Twin Boundary. Quantitative estimation of critical stress for various transmission phenomena is performed by using virial stress. Such information can be used as input for Discrete Dislocation Dynamics models [less ▲]

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See detailStudy of the Crystallization Behavior and the Subsequent Martensitic Transformation in a High Chromium Cast Steel submitted to Different Austenitization Temperatures
Tchuindjang, Jérôme Tchoufack ULg; Habraken, Anne ULg; Lecomte-Beckers, Jacqueline ULg

Conference (2015, September)

The crystallization behavior a High Chromium Cast Steel (HCCS) has been determined under Equilibrium conditions with ThermoCalc® software, and under non-Equilibrium conditions through Differential Thermal ... [more ▼]

The crystallization behavior a High Chromium Cast Steel (HCCS) has been determined under Equilibrium conditions with ThermoCalc® software, and under non-Equilibrium conditions through Differential Thermal Analyses (DTA). The results are compared to each other and the differences between the predicted solidification path and the actual one obtained from DTA (Figure 1) are highlighted. The microstructure in the as-cast conditions is characterized while using both scanning electron microscopy (SEM) and hardness measurements. The SEM analysis involves a combination of methods such as backscattered electron observation, energy dispersive spectrometry and backscattered-electron diffraction with X rays, which ensure proper identification of complex solidification carbides and the matrix made of martensite and retained austenite (Figure 2a). Solid state transformations occurring during the heating stage up to the austenitization temperature are studied towards both DTA and dilatometry, especially the dissolution/precipitation reactions. Different austenitization temperatures are considered prior to cooling down to room temperature during dilatometry tests to determine the starting points (Ms) for martensite transformation. In addition a cryogenic quenching within liquid nitrogen is performed which allows the completion of the martensitic transformation (Figure 2b) and help determining the critical point for the end of the martensitic reaction (Mf points). An enhanced discussion based on the influence of the cooling rate and the undercooling is developed to explain the differences that are observed between equilibrium and non-equilibrium conditions, which are mainly related to the solidification sequence and the carbides formed. The influence of the austenitization temperature and the matrix composition/supersaturation on both Ms and Mf points is also discussed. [less ▲]

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See detailImplementation of a damage evolution law for dual-phase steels in Gurson-type models
Balan, Tudor; Lemoine, Xavier; Maire, eric et al

in Materials and Design (2015), (88), 1213-1222

This paper is a contribution to the phenomenological modeling of damage evolution in DP steels in the framework of Gurson’s approach. It is based on recent results of X-ray tomography in-situ tensile ... [more ▼]

This paper is a contribution to the phenomenological modeling of damage evolution in DP steels in the framework of Gurson’s approach. It is based on recent results of X-ray tomography in-situ tensile tests and subsequent one-dimensional metallurgical void nucleation models proposed in [C. Landron et al., Scripta Materialia 63 (2010) 973—976]. A macroscopic void nucleation law for DP steels is proposed, covering a wide range of stress triaxialities. The respective effects of nucleation, growth and coalescence are clearly separated. Validations with respect to experimental porosity measurements were performed for several monotonic loading cases and for two loading sequences involving large strains and strain-path changes. [less ▲]

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See detailSize effects and temperature dependence on strain-hardening mechanisms in some face centered cubic materials
HUG, E.; DUBOS, P.A.; keller, C. et al

in Mechanics of Materials (2015), 91

The mechanical behaviour of face centered cubic metals is deeply affected when specimen dimensions decrease from a few The millimeters to a few micrometers. At room temperature, a critical thickness (t ... [more ▼]

The mechanical behaviour of face centered cubic metals is deeply affected when specimen dimensions decrease from a few The millimeters to a few micrometers. At room temperature, a critical thickness (t) to grain size (d) ratio (t/d)c, was previously highlighted, under which the sofiening of mechanical properties became very pronounced both in terms of Hall-Petch relation and work hardening mechanisms. In this work, new experimental results are provided concerning the influence of temperature on this size effect for copper, nickel and Ni-20wt.%Cr, representative of a wide range of deformation mechanisms (i.e. dislocation slip character). It is shown that multicrystalline samples (t/d < (t/d)c) are not deeply affected by an increase in temperature, independently of the planar or wavy character of dislocation glide. For pronounced wavy slip character metals, surface effects in polycrystals (t/d > (t/d)c) are not significant enough to reduce the gap between polycrystal and multierystal mechanical behaviour when the temperature increases. However, a transition from wavy slip to planar glide mechanisms induces a modification ofthe polycrystalline behaviour which tends tovard multicrystalline one with a moderate increase in temperature. This work demonstrates that surface effects and grain size influence can be successfully disassociated for the three studied materials using an analysis supported by the Kooks- Mecking formalism. All these results are supported by microscopic investigations of dislocation substructures and compared to numerical simulations using a stress gradient plasticity model. [less ▲]

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