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See detailAdaptive remeshing technique for the single incremental forming simulations using solid-shell elements
Velosa De Sena, José ULg; Guzmán Inostroza, Carlos Felipe ULg; Duchene, Laurent ULg et al

Scientific conference (2013, September 11)

Nowadays, conventional stamping is a well developed process. It is used for large production manufacturing which amortizes the cost of the tools. However, the possibility to use stamping processes for ... [more ▼]

Nowadays, conventional stamping is a well developed process. It is used for large production manufacturing which amortizes the cost of the tools. However, the possibility to use stamping processes for small volume production or prototypes can be still very expensive. As a result, the Single Point Incremental Forming (SPIF) emerges as a new possibility to solve the cost problem in small volume production. It is performed in a rapid and economic way without the need of expensive tooling. Its dieless nature makes the process appropriate for rapid prototypes and highly personalized pieces. Despite the progresses achieved during the last years, simulating SPIF through the Finite Element Method (FEM) continues nevertheless to be a demanding task. The constantly changing contact conditions between the tool and the sheet surface, as well as the nonlinear material model combined with non-monotonic strain paths during the forming process. In consequence, simulation time increases, even using shell hypothesis and simple geometries. Furthermore, the simulation with 3D “brick” elements in general increases the CPU time even more. To overcome this difficulty, an adaptive remeshing technique that was previously developed for the LAGAMINE code for shell elements [1] and afterwards extended to RESS (Reduced Enhanced Solid-Shell) finite element [2]. This allows that a portion of the sheet mesh is dynamically refined only in the tool vicinity, following its motion. Accordingly, this avoids the requirement of initially refined mesh and, consequently, the global CPU time is reduced. The current study will be focused in a benchmark simulation example applied to a component made by SPIF process using adaptive remeshing combined with RESS finite element. [less ▲]

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See detailUsing Gmsh as a mesh generator and post-processor for LAGAMINE
Guzmán Inostroza, Carlos Felipe ULg; Mouton, Thibaud ULg; Habraken, Anne ULg

Scientific conference (2013, September 11)

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See detailAccurate Single Point Incremental Forming Simulations using Solid-Shell Elements
Guzmán Inostroza, Carlos Felipe ULg; Sena, José Ilídio; Duchene, Laurent ULg et al

Scientific conference (2013, September 11)

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See detailStudy of phase transformations within bimetallic rolling mills
Neira Torres, Ingrid ULg; Lecomte-Beckers, Jacqueline ULg; Tchuindjang, Jérôme Tchoufack ULg et al

Scientific conference (2013, September 10)

With the aim of simulating the cooling behavior after a re-austenitizing stage of bimetallic rolling mills, both materials corresponding to spheroidal graphite iron (core material) and high chrome steel ... [more ▼]

With the aim of simulating the cooling behavior after a re-austenitizing stage of bimetallic rolling mills, both materials corresponding to spheroidal graphite iron (core material) and high chrome steel (shell material) must be characterized through thermo physical and mechanical tests as well as microscopic observations. Dilatometer tests were carried out for both materials in order to determinate thermo physical properties such as thermal expansion coefficient and density. Compression tests were also performed in order to estimate the effect of mechanical stress on martensite phase transformation, especially the nature and the type of martensite and start of transformation temperature. However there are some parameters that are still unknown and that are highly difficult to determinate. Inverse simulations are performed through Lagamine code with the aim of finding an estimated value for these parameters or improved parameters, more accurate than the ones already estimated. [less ▲]

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See detailNumerical investigation and experimental validation of physically-based advanced GTN model for DP steels
Fansi Tchonko, Joseph ULg; Balan, Tudor; Lemoine, Xavier et al

in Materials Science & Engineering : A (2013), 569

This numerical investigation of an advanced Gurson-Tvergaard-Needleman (GTN) model is an extension of the original work of [Ben Bettaieb, M., Lemoine, X., Bouaziz, O., Habraken, A.-M., Duchêne, L ... [more ▼]

This numerical investigation of an advanced Gurson-Tvergaard-Needleman (GTN) model is an extension of the original work of [Ben Bettaieb, M., Lemoine, X., Bouaziz, O., Habraken, A.-M., Duchêne, L., Numerical modeling of damage evolution of DP steels on the basis of X-ray tomography measurements, Mechanics of Materials 43 (2011) 139-156]. The current damage model extends the previous version by integrating the three damage mechanisms: nucleation, growth and coalescence of voids. Physically-based void nucleation and growth laws are considered, including an effect of the kinematic hardening. [less ▲]

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See detailParametric study of metal/polymer multilayer coatings for temperature wrinkling prediction
Zhang, Lihong ULg; Habraken, Anne ULg; Ben Bettaieb, Amine ULg et al

in Journal of Materials Engineering & Performance (2013), 22(9), 2437-2445

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See detailNumerical simulation of a pyramid steel sheet formed by single point incremental forming using solid-shell finite elements
Duchene, Laurent ULg; Guzmán Inostroza, Carlos Felipe ULg; Behera, Amar Kumar et al

in Key Engineering Materials [=KEM] (2013)

Single Point Incremental Forming (SPIF) is an interesting manufacturing process due to its dieless nature and its increased formability compared to conventional forming processes. Nevertheless, the ... [more ▼]

Single Point Incremental Forming (SPIF) is an interesting manufacturing process due to its dieless nature and its increased formability compared to conventional forming processes. Nevertheless, the process suffers from large geometric deviations when compared to the original CAD profile. One particular example arises when analyzing a truncated two-slope pyramid. In this paper, a finite element simulation of this geometry is carried out using a newly implemented solid-shell element, which is based on the Enhanced Assumed Strain (EAS) and the Assumed Natural Strain (ANS) techniques. The model predicts the shape of the pyramid very well, correctly representing the springback and the through thickness shear (TTS). Besides, the effects of the finite element mesh refinement, the EAS and ANS techniques on the numerical prediction are presented. It is shown that the EAS modes included in the model have a significant influence on the accuracy of the results. [less ▲]

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See detailNumerical modeling and digital image correlation strain measurements of coated metal sheets submitted to large bending deformation
Duchene, Laurent ULg; Ben Bettaieb, Amine ULg; Tuninetti Vásquez, Victor ULg et al

in Proceedings of the 16th ESAFORM conference on Material Forming (2013)

The recently developed SSH3D solid-shell element, which is based on the Enhanced Assumed Strain (EAS) and the Assumed Natural Strain (ANS) techniques, is utilized for the modeling of a severe bending ... [more ▼]

The recently developed SSH3D solid-shell element, which is based on the Enhanced Assumed Strain (EAS) and the Assumed Natural Strain (ANS) techniques, is utilized for the modeling of a severe bending sheet forming process. To improve the element's ability to capture the through thickness gradients, a specific integration scheme was developed. In this paper, the performances of this element for the modeling of the T-bent process were assessed thanks to comparison between experimental and numerical results in terms of the strain field at the outer surface of the sheet. The experimental results were obtained by Digital Image Correlation. It is shown that a qualitative agreement between experimental and numerical results is obtained but some numerical parameters should be optimized to improve the accuracy of the simulation predictions. In this respect, the influence of the penalty coefficient of the contact modeling was analyzed. [less ▲]

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See detailQUASI-STATIC MECHANICAL BEHAVIOUR OF TI-6AL-4V ALLOY AT ROOM TEMPERATURE
Tuninetti Vásquez, Victor ULg; Gilles, Gaëtan ULg; Milis, Olivier ULg et al

in Complas XII (2013), XII

In order to determine the mechanical behavior of a bulk TA6V alloy, a set of mechanical tests such as shear, compression, tensile monotonic tests, and tensile tests on notched samples are performed. The ... [more ▼]

In order to determine the mechanical behavior of a bulk TA6V alloy, a set of mechanical tests such as shear, compression, tensile monotonic tests, and tensile tests on notched samples are performed. The material is tested at constant strain rate. Full-field optical technique for displacement measurements and strain computation are used for all the experiments. Plastic anisotropy and tension–compression asymmetry are observed. The CPB06 [1] yield criterion adapted for hexagonal close packed (hcp) material is identified. The sensitivity of the material parameters on the identification method as well as the efficiency of the model to predict forces and displacement field are discussed. Validation is done by using Finite Element method (FEM) simulations and 3D Digital Image Correlation (3D-DIC) measurements on specimens with multi-axial stress and strain fields subjected to large deformation. [less ▲]

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See detailExperimental and numerical study of TA6V mechanical behavior under different quasi-static strain paths at room temperature
Gilles, Gaëtan ULg; Habraken, Anne ULg; Cazacu, Oana et al

in AIP Conference Proceedings (2013), 1532

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 ... [more ▼]

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. [less ▲]

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See detailTowards fracture prediction in single point incremental forming
Guzmán Inostroza, Carlos Felipe ULg; Habraken, Anne ULg

in Key Engineering Materials [=KEM] (2013), 554-557

The stress state in metal forming processes usually implies low values of triaxiality. It is well known that damage models based only on triaxiality fails to capture the damage behavior properly, and ... [more ▼]

The stress state in metal forming processes usually implies low values of triaxiality. It is well known that damage models based only on triaxiality fails to capture the damage behavior properly, and recent articles have stressed the effect of the Lode parameter in describing damage. Moreover, in some process like incremental forming, the through thickness shear could dominate the rupture mechanism making the description, using solely the triaxiality, inaccurate. In this paper, a preliminary study of the stress state is carried over a near-to-failure single point incremental forming (SPIF) formed cone, through finite elements simulations using a newly developed solid-shell element. The results provide a basis for further studies into damage development in SPIF. [less ▲]

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See detailPrediction of residual stresses by FE simulations on bimetallic work rolls during cooling
Neira Torres, Ingrid ULg; Gilles, Gaëtan ULg; Tchuindjang, Jérôme Tchoufack ULg et al

in Computer Methods in Materials Science (2013), 13(1), 84-91

Bimetallic rolls used in the roughing stands of the Hot Strip Mill require mixed properties as a high wear resistance for the shell material and an enhanced toughness for the core material. The bimetallic ... [more ▼]

Bimetallic rolls used in the roughing stands of the Hot Strip Mill require mixed properties as a high wear resistance for the shell material and an enhanced toughness for the core material. The bimetallic roll studied in this paper is obtained from a vertical spin casting process followed by cooling and subsequent heat treatments. Failure of the compound roll sometimes occurs during the cooling stage of the casting route or later during the thermal treatments. It requires to deeply investigate the thermo mechanical metallurgical interactions generated during cooling and heat treatment in order to find the origin of cracks. For this purpose, a thermo metallurgic mechanical finite element model is used. However these numerical simulations require a high amount of mechanical, thermal and metallurgical parameters. In order to determinate these parameters, a study of available data for estimation of mechanical parameters was performed. Thermo physical parameters were obtained by DTA and DSC methods. Metallurgical characterization by inverse numerical method based on available CCT diagrams was performed to determine the TTT diagrams. First cooling numerical simulations are presented, allowing a rough estimate of residual stresses values and the identification of key parameters for predicting accurate residual stresses by sensitivity analysis. [less ▲]

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See detailExperimental Characterisation of Damage Occuring during Single Point Incremental Forming of a Ferritic Steel
Mertens, Anne ULg; Guzmán Inostroza, Carlos Felipe ULg; Habraken, Anne ULg et al

Poster (2012, September)

Single Point Incremental Forming (SPIF) has been developed as a new dieless process for forming metal sheets. This technique appears very promising in view of the current requirements for rapid ... [more ▼]

Single Point Incremental Forming (SPIF) has been developed as a new dieless process for forming metal sheets. This technique appears very promising in view of the current requirements for rapid prototyping and/or small series production [1]. However, inaccuracies in the shape of the processed part and material failure constitute important limiting factors for applications. In the present research, a numerical approach, based on the damage model proposed by Gurson [2], has been chosen to analyse and optimise the process, predict the material rupture and the process limit. From experimental observations of plastic deformation and ductile fracture, damage is related to the nucleation, growth and coalescence of microvoids [3]. Gurson’s model uses the volume fraction of these voids as a main variable. Hence the determination of this value is a key factor for a correct identification and validation of the model. More particularly, the present work focuses on two different methods used to experimentally characterise damage occurring during single point incremental forming of a ferritic steel. Void measurements carried out by optical microscopy combined with image analysis have been compared with porosity values obtained from density measurements based on the Archimedes’ principle [4], so as to assess the feasibility of using this method for a quick characterisation of the damage. [less ▲]

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See detailStudy of the geometrical inaccuracy on a SPIF two-slope pyramid by finite element simulations
Guzmán Inostroza, Carlos Felipe ULg; Gu, Jun; Duflou, Joost et al

in International Journal of Solids and Structures (2012)

Single Point Incremental Forming (SPIF) is a recent manufacturing process which can give a symmetrical or asymmetrical shape to an undeformed metal sheet by using a relative small tool. In this article, a ... [more ▼]

Single Point Incremental Forming (SPIF) is a recent manufacturing process which can give a symmetrical or asymmetrical shape to an undeformed metal sheet by using a relative small tool. In this article, a two-slope SPIF pyramid with two different depths, which suffers from large geometric deviations when comparing the intended and final shapes, is studied. The article goal is to detect if these divergences are due to new plastic strain while forming the second angle pyramid by using finite elements simulations. To validate the numerical results, both the shape and the forces are compared with experimental measurements. Then, an analysis of the material state is carried out taking the equivalent plastic strain, von Mises effective stress and yield stress distribution through a cut in the mesh. It is noticed that there is plastic deformation in the center of the pyramid, far from the tool neighbourhood. Also, high values of stresses are observed under the yield stress in other parts of the sheet. As a strong bending behaviour plus membrane tension is found in some sheet elements, these elastic stresses are due to a bending action of the tool. It is concluded that the main shape deviations come from elastic strains due to structural elastic bending, plus a minor contribution of localized springback, as no plastic deformation is observed in the angle change zone. Future developments in toolpath designs should eventually consider these elastic strains in order to achieve the intended geometry. [less ▲]

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See detailTwinning in pure Ti subjected to monotonic simple shear deformation
Tirry, Wim; Bouvier, Salima; Benmhenni, Najoua et al

in Materials Characterization (2012), 72(October 2012), 2436

Two different textures of pure Ti were subjected to monotonic simple shear and this for three different orientations of the texture versus the shear direction. EBSD and TEM observations reveal the ... [more ▼]

Two different textures of pure Ti were subjected to monotonic simple shear and this for three different orientations of the texture versus the shear direction. EBSD and TEM observations reveal the presence of {10-12} and {11-22} twins. A statistical relevant analysis of the morphology of these twins combined with a resolved shear stress (RSS) analysis was performed. This analysis reveals that {10-12} and {11-22} twins have a similar average thickness, but the {10-12} twins show a far larger spread on their thickness compared to {11- 22} twins and can grow to almost the size of the original parent grain. Correlation of the twin fractions with the RSS analysis shows that this RSS technique is an acceptable method explaining the difference in twin fractions for different textures and orientations. A detailed analysis shows that {11-22} twins occur in average with a smaller volume fraction but with a higher RSS, indicating they are more difficult to nucleate or grow compared to {10-12} twinning. In general a higher RSS value on the twin plane is not connected with a higher twin thickness; only in case of {10-12} twins the highest RSS values show clearly thicker twins. [less ▲]

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See detailFinite element investigation of size effects on the mechanical behavior of nickel single crystals
Keller, Clément; Habraken, Anne ULg; Duchene, Laurent ULg

in Materials Science & Engineering : A (2012), 550(30), 342-349

The influence of dimensions on the mechanical behavior of f.c.c. single crystals with dimensions larger than a few micrometers has been the topic of many experimental investigations and controversies ... [more ▼]

The influence of dimensions on the mechanical behavior of f.c.c. single crystals with dimensions larger than a few micrometers has been the topic of many experimental investigations and controversies during the 1970s and this question is still open. The objective of this article is to shed new light on this point by performing finite element simulations thanks to a strain gradient crystal plasticity model. Based on the model identification for nickel, several single crystal samples with various thicknesses and orientations were tested numerically in tension. The effect of dimensions was then analyzed considering the spatial distribution of dislocation densities. Near loading boundaries, dislocation density gradients appeared perpendicular to the Burgers vector direction of the primary activated slip system which modified the mechanical behavior. These gradients are discussed in terms of boundary conditions, crystal orientation and dislocation interactions with surfaces. [less ▲]

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See detailA mixed solid-shell element for the analysis of laminated composites
Rah, Kamran; Paepegem, Wim; Habraken, Anne ULg et al

in International Journal for numerical methods in engineering (2012), 89(7), 805-828

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See detailEvaluation of the Enhanced Assumed Strain and Assumed Natural Strain in the SSH3D and RESS3 Solid Shell Elements for Single Point Incremental Forming Simulation
Guzmán Inostroza, Carlos Felipe ULg; Ben Bettaieb, Amine ULg; Velosa de Sena, José Ilidio et al

in Key Engineering Materials [=KEM] (2012), 504-506

Single Point Incremental Forming (SPIF) is a recent sheet forming process which can give a symmetrical or asymmetrical shape by using a small tool. Without the need of dies, the SPIF is capable to deal ... [more ▼]

Single Point Incremental Forming (SPIF) is a recent sheet forming process which can give a symmetrical or asymmetrical shape by using a small tool. Without the need of dies, the SPIF is capable to deal with rapid prototyping and small batch productions at low cost. Extensive research from both experimental and numerical sides has been carried out in the last years. Recent developments in the finite element simulations for sheet metal forming have allowed new modeling techniques, such as the Solid Shell elements, which combine the main features of shell hypothesis with a solid-brick element. In this article, two recently developed elements -SSH3D element [1, 2] and RESS3 element [3]- implemented in Lagamine (finite element code developed by the ArGEnCo department of the University of Liège) are explained and evaluated using the SPIF line test. To avoid locking problems, the well-known Enhanced Assumed Strain (EAS) and Assumed Natural Strain (ANS) techniques are used. The influence of the different EAS and ANS parameters are analysed comparing the predicted tool forces and the shape of a transversal cut, at the end of the process. The results show a strong influence of the EAS in the forces prediction, proving that a correct choice is fundamental for an accurate simulation of the SPIF using Solid Shell elements. [less ▲]

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