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See detailPhenomenological and crystal plasticity approaches to describe the mechanical behaviour of Ti6Al4V titanium alloy
Hammami, Walid ULg; Gilles, Gaëtan ULg; Habraken, Anne ULg et al

in International Journal of Material Forming (2011), 4(2), 205-2015

This paper presents a multiscale study of the quasi-static behaviour of a Ti6Al4V titanium alloy sheet. Tensile and compressive tests were carried out on specimens along several orientations from the ... [more ▼]

This paper presents a multiscale study of the quasi-static behaviour of a Ti6Al4V titanium alloy sheet. Tensile and compressive tests were carried out on specimens along several orientations from the rolling direction in order to characterise the material anisotropy. In parallel, X-Ray diffraction texture measurements were performed before and after deformation in tension. A phenomenological model (CPB06exn) and a multiscale crystal plasticity model (Multisite) were investigated to describe the mechanical behaviour of the tested material. The identification of the material parameters provides good predictions of the plastic anisotropy using both tensile and compressive data. The crystal plasticity model is in good agreement with the experiments in tension but it was observed that some improvements should be done to take into account the tension-compression asymmetry displayed by the material. Moreover both models lead to a good prediction of the Lankford’s coefficients and yield strength. [less ▲]

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See detailStrain Evolution in the Single Point Incremental Forming Process: Digital Image Correlation Measurement and Finite Element Prediction
Eyckens, P.; Belkassem, B.; Henrard, Christophe et al

in International Journal of Material Forming (2011)

Incremental Sheet Forming (ISF) is a relatively new class of sheet forming processes that allow the manufacture of complex geometries based on computer-controlled forming tools in replacement (at least ... [more ▼]

Incremental Sheet Forming (ISF) is a relatively new class of sheet forming processes that allow the manufacture of complex geometries based on computer-controlled forming tools in replacement (at least partially) of dedicated tooling. This paper studies the straining behaviour in the Single Point Incremental Forming (SPIF) variant (in which no dedicated tooling at all is required), both on experimental basis using Digital Image Correlation (DIC) and on numerical basis by the Finite Element (FE) method. The aim of the paper is to increase understanding of the deformation mechanisms inherent to SPIF, which is an important issue for the understanding of the high formability observed in this process and also for future strategies to improve the geometrical accuracy. Two distinct large-strain FE formulations, based on shell and first-order reduced integration brick elements, are used to model the sheet during the SPIF processing into the form of a truncated cone. The prediction of the surface strains on the outer surface of the cone is compared to experimentally obtained strains using the DIC technique. It is emphasised that the strain history as calculated from the DIC displacement field depends on the scale of the strain definition. On the modelling side, it is shown that the mesh density in the FE models plays a similar role on the surface strain predictions. A good qualitative agreement has been obtained for the surface strain components. One significant exception has however been found, which concerns the circumferential strain evolution directly under the forming tool. The qualitative discrepancy is explained through a mechanism of through-thickness shear in the experiment, which is not fully captured by the present FE modelling since it shows a bending-dominant accommodation mechanism. The effect of different material constitutive behaviours on strain prediction has also been investigated, the parameters of which were determined by inverse modelling using a specially designed sheet forming test. Isotropic and anisotropic yield criteria are considered, combined with either isotropic or kinematic hardening. The adopted constitutive law has only a limited influence on the surface strains. Finally, the experimental surface strain evolution is compared between two cones with different forming parameters. It is concluded that the way the plastic zone under the forming tool accommodates the moving tool (i.e. by through-thickness shear or rather by bending) depends on the process parameters. The identification of the most determining forming parameter that controls the relative importance of either mechanism is an interesting topic for future research. [less ▲]

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See detailA finite element analysis of the bending and the bendability of metallic sheets
Ben Bettaieb, Mohamed ULg; Lemoine, Xavier; Bouaziz, O. et al

in International Journal of Material Forming (2011), 4(3), 283-297

The main objective of this paper is to study the bendability of metallic sheets by using the finite element method. In this aim, two variants of an advanced Gurson-Tvergaard-Needleman model [1, 2] are ... [more ▼]

The main objective of this paper is to study the bendability of metallic sheets by using the finite element method. In this aim, two variants of an advanced Gurson-Tvergaard-Needleman model [1, 2] are implemented in the home made FE code LAGAMINE [3, 4] and coupled with the Thomason model to predict the coalescence of voids. This advanced model is an extension of the original one to take into account of the plastic anisotropy and the mixed (isotropic + kinematic) hardening of the matrix. The difference between the two variants is related to the modeling of the damage evolution. As the advanced model is used to study the bending process, its yield function is slightly modified in order to take into account the loadings with negative triaxiality ratios. These present implementations are used to simulate the pure bending process and to predict the bendability of dual phase (DP) steel. The combined effect of an initial geometrical imperfection and damage evolution on the bendability is also studied. [less ▲]

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See detailTemperature wrinkling prediction in metal/polymer multilayer coatings
Zhang, Lihong ULg; Ben Bettaieb, Amine ULg; Habraken, Anne ULg et al

in International Journal of Material Forming (2010, April), 3(supplement 1), 559-562

Two modeling approaches, analytical and numerical ones were carried out to simulate the mechanical behaviour of a coated metal steel sheet under thermo-mechanical loads. As the metallic film and the ... [more ▼]

Two modeling approaches, analytical and numerical ones were carried out to simulate the mechanical behaviour of a coated metal steel sheet under thermo-mechanical loads. As the metallic film and the polymer layer have different dilatation coefficients, temperature increase and/or humidity variation can result in a compressive state in the metallic film, and yield to bucking. This phenomenon is called wrinkling. It can be prevented by a stiff polymer layer or a stable film due to adapted thickness and mechanical properties. Wrinkling phenomenon has received increasing attention because of important uses of polymeric coating in many industrial applications. To better understand and predict this phenomenon, analytical and numerical models have been developed and compared. [less ▲]

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See detailBenefits of thixoforging hot-crack-sensitive aluminium alloys at high solid fraction
Vaneetveld, Grégory ULg; Rassili, Ahmed ULg; Pierret, Jean-Christophe ULg et al

in International Journal of Material Forming (2010), 2

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See detailMaterial data identification to model the single point incremental forming process
Bouffioux, Chantal ULg; Pouteau, P.; Duchene, Laurent ULg et al

in International Journal of Material Forming (2010), 3(Suppl. 1), 979-982

In this study, the Single Point Incremental Forming process (SPIF) is applied on a specific aluminium alloy used in the aerospace industry since this technique and material combine a low specific weight ... [more ▼]

In this study, the Single Point Incremental Forming process (SPIF) is applied on a specific aluminium alloy used in the aerospace industry since this technique and material combine a low specific weight, high strength and stiffness properties and high strain levels. To be able to optimize the process, a model and its material parameters are required. It was noticed that a simple isotropic hardening model was not sufficient to provide an accurate tool force prediction [1]. Therefore an elasto-plastic law with a mixed isotropic-kinematic hardening is investigated. The inverse method coupled with the Finite Element (FE) code: "Lagamine" [2] is used to fit the material data of this complex law. In order to validate the model and the material data, a Line test and a Cone test are used. [less ▲]

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See detailA one-field discontinuous Galerkin formulation of non-linear Kirchhoff-Love shells
Noels, Ludovic ULg

in International Journal of Material Forming (2009), 2(Suppl. 1), 877-880

Spatially-discontinuous Galerkin methods constitute a generalization of weak formulations, which allow for discontinuities of the problem unknowns in its domain interior. This is particularly appealing ... [more ▼]

Spatially-discontinuous Galerkin methods constitute a generalization of weak formulations, which allow for discontinuities of the problem unknowns in its domain interior. This is particularly appealing for problems involving high-order derivatives, since discontinuous Galerkin (DG) methods can also be seen as a means of enforcing higher-order continuity requirements. Recently, DG formulations of linear and non-linear Kirchhoff-Love shell theories have been proposed. This new one-field formulations take advantage of the weak enforcement in such a way that the displacements are the only discrete unknowns, while the C1 continuity is enforced weakly. The Resulting one field formulation is a simple and efficient method to model thin structures and can be applied to various computational methods. [less ▲]

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See detailCrystal plasticity prediction of Lankford coefficient using the MULTISITE model: influence of the critical resolved shear stresses
Hammami, Walid ULg; Delannay, Laurent; Duchene, Laurent ULg et al

in International Journal of Material Forming (2009, August), 2(Supplément 1), 65-68

The MULTISITE model [1] is based on polycrystalline plasticity and the underlying hypotheses of the model are (i) that the deformation of each grain is significantly influenced by the interaction with a ... [more ▼]

The MULTISITE model [1] is based on polycrystalline plasticity and the underlying hypotheses of the model are (i) that the deformation of each grain is significantly influenced by the interaction with a limited number of adjacent grains, and (ii) that local strains deviate from their macroscopic average according to specific “relaxation modes”. The LAMEL model [2] is reformulated into the more general elastic-viscoplastic MULTISITE model permitting various relaxation modes. This model has been validated for cubic materials but hexagonal close-packed (HCP) crystals usually demonstrate larger anisotropy than cubic crystals. The model was used to simulate uniaxial tensile tests performed on rolled sheets made of Ti-6Al-4V. The Lankford coefficients (r) calculated in various directions in the plane of the sheet were analysed. In this study, different grain interaction hypotheses were tested. Besides, it appeared that the value of the critical resolved shear stresses (CRSS) of the different slip system families of the HCP metal had significant effects on the results. Their influence as well as the influence of the strain rate sensitivity parameter was examined. [less ▲]

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See detailEvaluation of different advanced finite element concepts for detailed stress analysis of laminated composite structures
Rah, K.; Van Paepegem, W.; Habraken, Anne ULg et al

in International Journal of Material Forming (2009), volume 2(Supplément 1), 943-947

Despite their high specific stiffness and strength, laminated composite materials, e.g. fibre-reinforced plastic plies stacked at different fibre orientations, are susceptible to damage. Damage can be ... [more ▼]

Despite their high specific stiffness and strength, laminated composite materials, e.g. fibre-reinforced plastic plies stacked at different fibre orientations, are susceptible to damage. Damage can be divided into interalaminar damage and interlaminar damage. Delamination is a typical kind of interlaminar damage which occurs in laminated composite materials, often accompanied with intralaminar damage, and may lead to a catastrophic structural collapse. The first and most crucial step in the prediction of failure of Laminated Composite Structures (LCS) is to accurately determine the stresses, particularly the three transverse stress components, also called the interlaminar stresses. It is proposed in the present paper that the integration of a displacement based solid-shell formulation and partial-hybrid stress formulation will lead to an accurate and robust solid-shell element, suitable for the efficient and detailed interlaminar stress calculation. [less ▲]

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See detailElectron backscattered diffraction of aluminium alloy 7075 samples after heat treatment
Vaneetveld, Grégory ULg; Rassili, Ahmed ULg; Lecomte-Beckers, Jacqueline ULg et al

in International Journal of Material Forming (2009)

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.7<fs<1), which involves the processing of alloys in the semi-solid state. The use of semi-solid material with globular ... [more ▼]

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.7<fs<1), which involves the processing of alloys in the semi-solid state. The use of semi-solid material with globular microstructure helps to decrease forming load. But the introduction of a liquid phase in the material is a source of defects that limit mechanical properties of thixoforged parts. One of these defects is the hot cracking for some hot crack-sensitive wrought aluminium alloys. Hot cracking occurs because of strain and deformation during last step of solidification. This paper shows how thixoforging process should help to lower hot cracking tendency without modification of the alloy composition by decreasing strain and deformation due to shrinkage. Different experimental tests by extrusion of 7075 aluminium alloys are used. [less ▲]

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See detailInfluence of the chemical composition on the thixoformability of steels
Pierret, Jean-Christophe ULg; Rassili, Ahmed ULg; Vaneetveld, Grégory ULg et al

in International Journal of Material Forming (2009)

This work deals with the qualification of a variety of steels for their shaping by the thixoforging process. This technology requires setting up a globular microstructure inside the material during ... [more ▼]

This work deals with the qualification of a variety of steels for their shaping by the thixoforging process. This technology requires setting up a globular microstructure inside the material during reheating to a temperature between the solidus and liquidus. As the evolution of the liquid fraction is strongly connected to the steel composition, it is useful to understand how low carbon steel could be alloyed and still thixoformable. The most critical parameter for this is the carbon content. In this study, a theoretical analysis of the phase evolution during the reheating has been performed on the MT Data software to investigate the influence of alloying elements. These first results have been confirmed by Differential Thermal Analysis and by inductive heating experiments on steel slugs. Finally, some parts have been shaped using a thixoforming tool mounted on a hydraulic press. Micrographs of reheated slugs as well as of actual parts are also presented in this paper. [less ▲]

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See detailMetallurgical and mechanical analysis from thixoforging steel shape
Becker, Eric; Bigot, Regis; Langlois, Laurent et al

in International Journal of Material Forming (2008), 1(1), 977-980

Since always, Industry minimizes manufacturing process plan and increases mechanical behaviour. In this topic, the thixoforging process offers important perspectives especially steel thixoforging. It is ... [more ▼]

Since always, Industry minimizes manufacturing process plan and increases mechanical behaviour. In this topic, the thixoforging process offers important perspectives especially steel thixoforging. It is on the way of industrial development between casting and forging process. Previous works have illustrated the importance many parameters such as steel grade, slide speed, slug and tool temperature on the geometry from thixoforging part and of the forming load. This paper completes the previous results. It presents an analysis from mechanical resistance of samples extracted of from thixo-extrusion parts on a high speed hydraulic press. This strength investigation is correlated with metallurgical analysis. Macrograph analyses allow identifying the material yield during the process and the different phases. [less ▲]

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See detailInfluence of Alloying Elements on the Thixoformability of a Chromium Steel
Fraipont, Céline; Lecomte-Beckers, Jacqueline ULg

in International Journal of Material Forming (2008), 1(1), 997-1000

This paper deals with the examination of the influence of alloying elements on the thixoformability of a chromium steel. It focuses on the liquid fraction curves of various chromium steels with and ... [more ▼]

This paper deals with the examination of the influence of alloying elements on the thixoformability of a chromium steel. It focuses on the liquid fraction curves of various chromium steels with and without modification of composition. The liquid fraction versus temperature has been obtained by MTData, a thermodynamic prediction package, and by Differential Thermal Analysis (DTA), limited to low heating rates. The correlation between liquid fraction and temperature has been studied. The effect of modifications of composition and of heating rate was observed. First, the thermodynamical calculations allow the study of the influence of alloying elements with variations in chemical composition. Secondly, the DTA tests offer the possibility to observe the influence of heating rate on liquid fraction curve parameters. All these results lead to the identification of the initial parameters necessary to perform inductive heating and quenching tests, and so to approach the industrial process. [less ▲]

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See detailExtrusion tests of 7075 aluminium alloy at high solid fraction
Vaneetveld, Grégory ULg; Rassili, Ahmed ULg; Pierret, Jean-Christophe ULg et al

in International Journal of Material Forming (2008), 1(1), 1019-1022

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5<fs<1). 7075 aluminium alloy has been used as a feedstock for thixoforging in order to investigate thixoformability of a ... [more ▼]

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5<fs<1). 7075 aluminium alloy has been used as a feedstock for thixoforging in order to investigate thixoformability of a high performance aluminium alloy at high solid fraction. Higher solid fraction of 7075 alloy is less sensitive to a drop in temperature, avoids metal splash at high speed, allows laminar flow at high speed. Hot tool is used to slow down the solidification rate of the high solid fraction metal by decreasing thermal exchanges. To determine the best parameters to achieve maximum mechanical properties in thixoforging of 7075 aluminum alloy, we need to consider the impact of some parameters such as tool temperature, shear rate. For this, we use extrusion tests with constant speed [1] where these parameters are known. The result of this study is that each parameter has its level of impact on the thixoforging: the temperature of the tool and the deformation rate shouldn't be high to avoid cracks. Thermal exchanges between the material flow and the tool have to be reduced to avoid high solidification rate [2]. [less ▲]

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See detailRecrystallisation in the semi-solid state in 7075 aluminium alloy
Atkinson, Helen Victoria; Burke, Karen; Vaneetveld, Grégory ULg

in International Journal of Material Forming (2008), 1(Suppl 1), 973-976

7000 series aluminium alloys are currently machined from the wrought state with much waste. There is therefore a motivation to identify effective near net shaping routes. Semi-solid processing is one such ... [more ▼]

7000 series aluminium alloys are currently machined from the wrought state with much waste. There is therefore a motivation to identify effective near net shaping routes. Semi-solid processing is one such potential route. It relies on the thixotropic behaviour of alloys with non-dendritic spheroidal microstructures. In the semisolid state the material thins when sheared and will flow to fill the die. When worked material is reheated, it recrystallises and moving into the semi-solid state, the required spheroidal microstructure develops. Here we examine the early stages of spheroid formation in 7075 aluminium alloy reheated from the as-supplied T6 condition. This alloy is very resistant to recrystallisation in the solid state due to the presence of dispersoid particles pinning grain boundaries. There is a sudden increase in the appearance of spheroidal grains. There is a close association with the position of the first liquid to form. On reheating as-supplied material to around 580°C (fraction of liquid ~5%), a fully spheroidal microstructure can be obtained. [less ▲]

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See detailSteel thixoforming, influence of forming parameters on the microstructure
Pierret, Jean-Christophe ULg; Rassili, Ahmed ULg; Vaneetveld, Grégory ULg et al

in International Journal of Material Forming (2008), 1(1), 1011-1014

Forming of parts in the semi-solid state is quite a complex process, especially for high melting point alloys such as steel. A reason for this complexity is the amount of parameters involved in the ... [more ▼]

Forming of parts in the semi-solid state is quite a complex process, especially for high melting point alloys such as steel. A reason for this complexity is the amount of parameters involved in the process. Among these we could quote liquid fraction, shear rate, shape factor, contiguity, tool temperature, agglomeration level, heating rate, protecting gas, temperature distribution, lubricant. Of course all of these parameters don’t have the same order of importance. In this paper we show the influence of a set of chosen parameters and we highlight their effects on the microstructure and so, on the deformation behavior. The studied parameters are the heating conditions, the tool temperature, the part temperature, the thermal exchanges between the part and the dies and the forming rate. [less ▲]

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See detailIdentification of material parameters to predict Single Point Incremental Forming forces
Bouffioux, Chantal ULg; Eyckens, P.; Henrard, Christophe et al

in International Journal of Material Forming (2008)

The purpose of this article is to develop an inverse method for adjusting the material parameters for single point incremental forming (SPIF). The main idea consists in FEM simulations of simple tests ... [more ▼]

The purpose of this article is to develop an inverse method for adjusting the material parameters for single point incremental forming (SPIF). The main idea consists in FEM simulations of simple tests involving the SPIF specificities (the “line test”) performed on the machine used for the process itself. This approach decreases the equipment cost. It has the advantage that the material parameters are fitted for heterogeneous stress and strain fields close to the ones occurring during the actual process. A first set of material parameters, adjusted for the aluminum alloy AA3103 with classical tests (tensile and cyclic shear tests), is compared with parameters adjusted by the line test. It is shown that the chosen tests and the strain state level have an important impact on the adjusted material data and on the accuracy of the tool force prediction reached during the SPIF process. [less ▲]

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See detailA one-phase thermomechanical constitutive model for the numerical simulation of semi-solid thixoforming
Koeune, Roxane ULg; Ponthot, Jean-Philippe ULg

in International Journal of Material Forming (2008), suppl. 1

A thermomechanical one-phase elasto-visco-plastic constitutive law has been developed in order to model thixoforming processes. The simulation of a simple academic 2D test has revealed the forces and ... [more ▼]

A thermomechanical one-phase elasto-visco-plastic constitutive law has been developed in order to model thixoforming processes. The simulation of a simple academic 2D test has revealed the forces and weaknesses of the proposed model. [less ▲]

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