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Comparison of a Fluid and a Solid Approach for the Numerical Simulation of Friction Stir Welding with a Non‐Cylindrical Pin Bussetta, Philippe ; ; Boman, Romain et al in Steel Research International (2014), 85(6), 968-979 Friction stir welding (FSW) process is a solid‐state joining process during which materials to be joined are not melted. As a consequence, the heat‐affected zone is smaller and the quality of the weld is ... [more ▼] Friction stir welding (FSW) process is a solid‐state joining process during which materials to be joined are not melted. As a consequence, the heat‐affected zone is smaller and the quality of the weld is better with respect to more classical welding processes. Because of extremely high strains in the neighborhood of the tool, classical numerical simulation techniques have to be extended in order to track the correct material deformations. The Arbitrary Lagrangian–Eulerian (ALE) formulation is used to preserve a good mesh quality throughout the computation. With this formulation, the mesh displacement is independent from the material displacement. Moreover, some advanced numerical techniques such as remeshing or a special computation of transition interface is needed to take into account non‐cylindrical tools. During the FSW process, the behavior of the material in the neighborhood of the tool is at the interface between solid mechanics and fluid mechanics. Consequently, a numerical model of the FSW process based on a solid formulation is compared to another one based on a fluid formulation. It is shown that these two formulations essentially deliver the same results in terms of pressures and temperatures. [less ▲] Detailed reference viewed: 44 (9 ULg)Effect of the kinematic hardening in the simulations of the straightening of long rolled profiles Bouffioux, Chantal ; Boman, Romain ; et al in Key Engineering Materials [=KEM] (2014), 611-612 Residual stresses and lack of straightness appear during the cooling of sheet piles where the initial temperature field is not homogeneous. To meet the standards, the long hot rolled pieces are ... [more ▼] Residual stresses and lack of straightness appear during the cooling of sheet piles where the initial temperature field is not homogeneous. To meet the standards, the long hot rolled pieces are straightened using a series of rollers placed alternately above and below the pieces with shifts which create a succession of bendings. The process is modeled to study the impact of the industrial parameters ( the duration of the cooling and the rollers positions), to improve the final geometry and to reduce the residual stresses.Tests are carried out on this structural steel to observe the material behavior, then material laws are chosen and parameters of these laws are defined using and inverse method. Two sets of material data are obtained: for the first one, the hardening is supposed to be isotropic, and for the second one, additional tests are performed to describe isotropic and kinematic hardenings.The cooling followed by the straightening is then simulated by the finite element with these two sets of date. The comparison of the rollers forces, the deformation and the residual stresses show the impact of the kinematic hardening on such a process where the material undergoes a sucession of the tensions and compressions. The real forces applied by the rollers,the real curvature of the interlocks at the end of the straightening process and the distribution of the residual longitudinal stresses measured on the web using the ring core method are used to validate the numerical model. [less ▲] Detailed reference viewed: 34 (14 ULg)Arbitrary Lagrangian Eulerian simulations of stationary and non-stationary metal forming processes Boman, Romain ; Ponthot, Jean-Philippe in AIP Conference Proceedings (2013, December 16), 1567 Detailed reference viewed: 51 (27 ULg)An implicit erosion algorithm for the numerical simulation of metallic and composite materials submitted to high strain rate. Ponthot, Jean-Philippe ; Boman, Romain ; et al in Proceedings Indian National Science Academy (2013), 79/4(Part A), 519-528 In this paper, we present a general consistent numerical formulation able to take into account strain rate, damage and thermal effects of the material behaviour. A thermomechanical implicit approach for ... [more ▼] In this paper, we present a general consistent numerical formulation able to take into account strain rate, damage and thermal effects of the material behaviour. A thermomechanical implicit approach for element erosion to model material failure is also presented. This approach can be applied both to ductile fracture for metals, relying on a continuum damage mechanics approach, coupled to different fracture criteria, as well as composite material failure described with either a failure criterion or a progressive damage model. The numerical models will be illustrated by different quasi-static and high strain rate applications for both metallic alloys and composite materials. All these physical phenomena have been included in an implicit dynamic object-oriented finite element code (implemented at LTAS-MN²L, University of Liège, Belgium) named Metafor [1]. [less ▲] Detailed reference viewed: 82 (7 ULg)Numerical simulation of the Roll forming of thin-walled sections and evaluation of corner strength enhancement Rossi, Barbara ; Degée, Hervé ; Boman, Romain in Finite Elements in Analysis & Design (2013), 72 Cold roll forming modifies the mechanical properties of thin-walled profiles by strain hardening. The understanding of this phenomenon, which is rather good for profiles made of traditional construction ... [more ▼] Cold roll forming modifies the mechanical properties of thin-walled profiles by strain hardening. The understanding of this phenomenon, which is rather good for profiles made of traditional construction steel, is mandatory for assessing the member resistance. Less information is however available for profiles made of materials exhibiting a pronounced degree of nonlinearity of the stress-strain curve such as high-strength and stainless steels. Current codes generally encounter difficulties for modelling this fabrication process because of the size of industrial mills. Indeed, accurate modelling of the continuous cold roll forming process using finite elements requires a huge number of elements leading to excessive CPU times. Therefore, modellers usually reduce the geometry of the formed sheet or increase the size of the finite elements, inducing a loss of accuracy in the results. In this work, the finite element software METAFOR is used to model cold roll forming of channel profiles made of high-strength and stainless steels. The numerical results, expressed in terms of corner strength enhancement versus radius–to–thickness ratio, are compared against an existing predictive model. [less ▲] Detailed reference viewed: 133 (34 ULg)Verification of a novel material model to predict damage in composite structures ; ; Boman, Romain et al in International Conference on Structural Integrity and Fracture (2013, July 11) An intralaminar damage model (IDM), based on continuum damage mechanics, was developed for the simulation of composite structures subjected to damaging loads. This model can capture the complex ... [more ▼] An intralaminar damage model (IDM), based on continuum damage mechanics, was developed for the simulation of composite structures subjected to damaging loads. This model can capture the complex intralaminar damage mechanisms, accounting for mode interactions, and delaminations. Its development is driven by a requirement for reliable crush simulations to design composite structures with a high specific energy absorption. This IDM was implemented as a user subroutine within the commercial finite element package, Abaqus/Explicit[1]. In this paper, the validation of the IDM is presented using two test cases. Firstly, the IDM is benchmarked against published data for a blunt notched specimen under uniaxial tensile loading, comparing the failure strength as well as showing the damage. Secondly, the crush response of a set of tulip-triggered composite cylinders was obtained experimentally. The crush loading and the associated energy of the specimen is compared with the FE model prediction. These test cases show that the developed IDM is able to capture the structural response with satisfactory accuracy. [less ▲] Detailed reference viewed: 63 (6 ULg)Contributions to the process modelling of resin infusion under flexible tooling (RIFT) manufacturing for composite aerostructures ; ; et al in Proceedings of ICCM19 (2013, July) The cost of manufacturing textile-reinforced composite aerostructures using Resin Infusion under Flexible Tooling (RIFT) can be reduced by computational modelling. This paper outlines the current progress ... [more ▼] The cost of manufacturing textile-reinforced composite aerostructures using Resin Infusion under Flexible Tooling (RIFT) can be reduced by computational modelling. This paper outlines the current progress and contributions made towards this goal. A continuum-based material model was incorporated into a finite element package to simulate the draping of a dry carbon fibre fabric. It accurately tracks the changes in the warp and weft fibre orientations and has been experimentally validated. Material characterisation was performed to determine the tensile and shear properties of a plain weave fabric reinforcement material. In support of bias extension shear testing, an accessible Digital Image Correlation (DIC) approach was developed for accurate optical strain measurement. A relationship between permeability and shear angle was also experimentally determined using a novel permeability measurement technique. Future work is planned to combine all these aspects in an infusion model and demonstrate the complete process model. [less ▲] Detailed reference viewed: 74 (0 ULg)Numerical simulations of asperity crushing using boundary conditions encountered in cold-rolling Carretta, Yves ; Boman, Romain ; et al in Key Engineering Materials [=KEM] (2013), 554-557 Asperity flattening has a huge influence on friction and wear in metal forming processes. Nevertheless, phenomena that occur at the microscopic scale are still not well understood. Since no experiment can ... [more ▼] Asperity flattening has a huge influence on friction and wear in metal forming processes. Nevertheless, phenomena that occur at the microscopic scale are still not well understood. Since no experiment can be easily performed in real forming conditions, numerical models are essential to achieve a better knowledge of what happens in these contact regions. In this paper, two finite elements models are presented. The first one represents the flattening of a serrated asperity field in plane-strain conditions. The results are compared to the experiments published by Sutcliffe [1]. The second one is a tri-dimensional asperity model flattened by a rigid plane. The boundary conditions applied to this model correspond to the ones encountered in a real cold-rolling case. The results are compared to the relative contact area computed by a strip rolling model using the analytical laws proposed by Wilson & Sheu [2] and Marsault [3]. [less ▲] Detailed reference viewed: 83 (46 ULg)Numerical Simulation of Double Cup Extrusion Test using the Arbitrary Lagrangian Eulerian Formalism Boman, Romain ; ; Ponthot, Jean-Philippe in Proceedings of Coupled Problems 2013 (2013, June) Detailed reference viewed: 57 (22 ULg)Comparison of a fluid and a solid approach for the numerical simulation of Friction Stir Welding with a non-cylindrical pin Bussetta, Philippe ; ; Boman, Romain et al in Proceedings of "V International Conference on Computational Methods for Coupled Problems in Science and Engineering" (2013, June) Friction Stir Welding (FSW) process is a solid-state joining process during which materials to be joined are not melted. As a consequence, the heat-affected zone is smaller and the quality of the weld is ... [more ▼] Friction Stir Welding (FSW) process is a solid-state joining process during which materials to be joined are not melted. As a consequence, the heat-affected zone is smaller and the quality of the weld is better with respect to more classical welding processes. Because of extremely high strains in the neighbourhood of the tool, classical numerical simulation techniques have to be extended in order to track the correct material deformations. The Arbitrary Lagrangian Eulerian (ALE) formulation is used to preserve a good mesh quality throughout the computation. With this formulation the mesh displacement is independent from the material displacement. Moreover, some advanced numerical techniques such as remeshing or a special computation of transition interface is needed to take into account non-cylindrical tools. During the FSW process, the behaviour of the material in the neighbourhood of the tool is at the interface between solid mechanics and fluid mechanics. Consequently, a numerical model of the FSW process based on a solid formulation is compared to another one based on a fluid formulation. It is shown that these two formulations essentially deliver the same results in terms of pressures and temperatures. [less ▲] Detailed reference viewed: 84 (16 ULg)Enhanced ALE Data Transfer Strategy for Explicit and Implicit Thermomechanical Simulations of High-Speed Processes Boman, Romain ; Ponthot, Jean-Philippe in International Journal of Impact Engineering (2013), 53 The Arbitrary Lagrangian Eulerian (ALE) formalism, which allows the computational grid to move regardless of thematerial deformation, is a convenient way to avoid distortedmeshes in finite element ... [more ▼] The Arbitrary Lagrangian Eulerian (ALE) formalism, which allows the computational grid to move regardless of thematerial deformation, is a convenient way to avoid distortedmeshes in finite element simulations. One crucial step of the ALE algorithm is the data transfer between the Lagrangian and the Eulerian meshes. In this paper, an enhanced transfer method is presented. It can handle complex finite elements which are integrated with more than one Gauss point. This method can thus be used either with an explicit or with an implicit time integration scheme. Choosing the adequate order of accuracy and the most appropriate number of physical fields to be transferred is always a compromise between the speed and the precision of the model. For example, some variables may be sometimes ignored during the transfer in order to decrease the CPU time. Therefore, the most effective way to use such an algorithm is demonstrated in this work by revisiting a classical ALE benchmark, the Taylor impact. An implicit thermomechanical ALE simulation of a high-speed tensile test is also presented and is compared to experimental results from the literature. [less ▲] Detailed reference viewed: 45 (19 ULg)Relating Local Permeability Changes to the Deformation of Preforms during the Manufacture of Complex-Shaped Composite Structures ; ; Boman, Romain in Proceedings of the 15th Australian Aeronautical Conference (2013, February) The transition to using carbon-fibre composites in the primary structure of passenger aircraft is now well established with focus shifting towards reducing manufacturing costs. This study reports on ... [more ▼] The transition to using carbon-fibre composites in the primary structure of passenger aircraft is now well established with focus shifting towards reducing manufacturing costs. This study reports on initial results in the development of accurate numerical process modelling tools for resin-infused composite structures. A continuum-based, finite element material model has been developed to simulate the draping of a dry carbon fibre fabric, accurately tracking the changes in the warp and weft fibre orientations. A multiple ply draping example demonstrates the large variation of shear angles that are prevalent in forming processes. The relationship between shear angle and permeability was studied experimentally as it is integral to the accuracy of the resin infusion modelling process. The anisotropic permeability of the plain weave fabric was observed to increase by a factor of five as the shear locking angle was approached, with principal permeability values, K1 and K2, increasing and decreasing by a factor of approximately two, respectively. [less ▲] Detailed reference viewed: 54 (2 ULg)A Continuum Damage Mechanics Model for the Analysis of the Crashworthiness of Composite Structures: A work in progress ; ; Boman, Romain in Proceedings of the 15th Australian Aeronautical Conference (2013, February) The crashworthiness capability of an aircraft structure is dependent on its ability to attenuate crash loading via the controlled deformation of energy absorbing devices. An energy-based constitutive ... [more ▼] The crashworthiness capability of an aircraft structure is dependent on its ability to attenuate crash loading via the controlled deformation of energy absorbing devices. An energy-based constitutive relation was employed to model the behaviour of carbon fibre reinforced epoxy resin composite material under crush loading. Each of the damage modes in the fibre and matrix was treated separately with its own damage initiation and progression relationships as well as a damage parameter that tracks damage progression. Each damage parameter dictates the reduction in stiffness in the respective principal loading directions. This model was implemented for a 3D solid brick element in contrast to shell-based formulations currently available. Crushing composite structures were modelled and the results validated against experimental data. The force-displacement response / specific energy absorption and the failure modes obtained from the simulation show that the underlying physics of the crushing have been captured by the proposed model but that further work is required for reliable quantitative correlation. [less ▲] Detailed reference viewed: 113 (8 ULg)A continuous fluid/solid transition model for semi-solid material modeling. Application to thixoforging. Ponthot, Jean-Philippe ; ; Boman, Romain in 33° SENAFOR (CD) (2013) This paper deals with the simulation of two extrusion tests by thixoforming: a non stationary extrusion test and a double-cup extrusion test. The simulations are based on a thermo-mechanical one-phase ... [more ▼] This paper deals with the simulation of two extrusion tests by thixoforming: a non stationary extrusion test and a double-cup extrusion test. The simulations are based on a thermo-mechanical one-phase constitutive law that has been presented in details in several previous papers. A campaign of experimental extrusion testing has been conducted on a steel alloy and the comparison between the numerical and experimental results will validate the model under study. A new feature that has been added to the model is also discussed: the introduction of the phase change thermal effects such as the fusion latent heat and the contraction of the material [less ▲] Detailed reference viewed: 38 (8 ULg)Efficient ALE mesh management for 3D quasi-Eulerian problems Boman, Romain ; Ponthot, Jean-Philippe in International Journal for Numerical Methods in Engineering (2012), 92(10), 857-890 In computational solid mechanics, the ALE formalism can be very useful to reduce the size of finite element models of continuous forming operations such as roll forming. The mesh of these ALE models is ... [more ▼] In computational solid mechanics, the ALE formalism can be very useful to reduce the size of finite element models of continuous forming operations such as roll forming. The mesh of these ALE models is said to be quasi-Eulerian because the nodes remain almost fixed—or almost Eulerian—in the main process direction, although they are required to move in the orthogonal plane in order to follow the lateral displacements of the solid. This paper extensively presents a complete node relocation procedure dedicated to such ALE models. The discussion focusses on quadrangular and hexahedral meshes with local refinements. The main concern of this work is the preservation of the geometrical features and the shape of the free boundaries of the mesh. With this aim in view, each type of nodes (corner, edge, surface and volume) is treated sequentially with dedicated algorithms. A special care is given to highly curved 3D surfaces for which a CPU-efficient smoothing technique is proposed. This new method relies on a spline surface reconstruction, on a very fast weighted Laplacian smoother with original weights and on a robust reprojection algorithm. The overall consistency of this mesh management procedure is finally demonstrated in two numerical applications. The first one is a 2D ALE simulation of a drawbead, which provides similar results to an equivalent Lagrangian model yet is much faster. The second application is a 3D industrial ALE model of a 16-stand roll forming line. In this case, all attempts to perform the same simulation by using the Lagrangian formalism have been unsuccessful. [less ▲] Detailed reference viewed: 63 (16 ULg)Three-dimensional Modelling of Asperity Crushing Carretta, Yves ; Boman, Romain ; et al Conference (2012, October) Asperity flattening has a huge influence on friction and wear in metal forming processes. Nevertheless, phenomena that occur at the microscopic scale are still not well understood. Since no experiment can ... [more ▼] Asperity flattening has a huge influence on friction and wear in metal forming processes. Nevertheless, phenomena that occur at the microscopic scale are still not well understood. Since no experiment can be easily performed in real forming conditions, numerical models are essential to achieve a better knowledge of what happens in these contact regions. In this paper, a threedimensional model of a rough strip flattened by a rigid rough tool is presented. The boundary conditions applied to this model correspond to the ones encountered in a real cold-rolling case. The results are compared to experimental measurements from the pilot mill of ArcelorMittal Maizières R&D. [less ▲] Detailed reference viewed: 34 (13 ULg)Arbitrary Lagrangian Eulerian Modelling of Tension Levelling Boman, Romain ; ; et al in Matériaux et Techniques (2012, October), 100(Hors série 2012), 40-42 This paper presents a two-dimensional model of tension levelling using the Arbitrary Lagrangian Eulerian (ALE) approach. During the simulation, the ALE mesh remains globally fixed along the rolling ... [more ▼] This paper presents a two-dimensional model of tension levelling using the Arbitrary Lagrangian Eulerian (ALE) approach. During the simulation, the ALE mesh remains globally fixed along the rolling direction. Therefore, the required number of finite elements is much smaller than in the Lagrangian case and smaller CPU times are obtained for the same accuracy on the results. The ALE model is first validated against a classical equivalent Lagrangian model. Then, both sets of numerical results are compared to experimental measurements from the pilot mill of ArcelorMittal Maizières R&D. [less ▲] Detailed reference viewed: 59 (8 ULg)Mixed Lubrication Regime in Cold Strip Rolling Carretta, Yves ; Boman, Romain ; et al in 2nd Annual ArcelorMittal CFD and Thermomechanics Days 2012 (2012, January) Detailed reference viewed: 20 (8 ULg)ALE Simulations of Metal Forming Processes Boman, Romain ; Ponthot, Jean-Philippe in Akhtar S. Khan; Farhoud Kabirian; Jian Liu (Eds.) Non-linear Response of Conventional & Advanced Materials, and Multi-scale Modeling (2012, January) Detailed reference viewed: 54 (9 ULg)Generating smooth surface meshes from multi-region medical images D'Otreppe, Vinciane ; Boman, Romain ; Ponthot, Jean-Philippe in International Journal for Numerical Methods in Biomedical Engineering (2012), 28(6-7), 642-660 Thanks to advances in medical imaging technologies and numerical methods, Patient-Specific Modelling is more and more used to improve diagnosis and to estimate the outcome of surgical interventions. It ... [more ▼] Thanks to advances in medical imaging technologies and numerical methods, Patient-Specific Modelling is more and more used to improve diagnosis and to estimate the outcome of surgical interventions. It requires the extraction of the domain of interest from the medical scans of the patient, as well as the discretisation of this geometry. However, extracting smooth multi-material meshes that conform to the tissue boundaries described in the segmented image is still an active field of research. We propose to solve this issue by combining an implicit surface reconstruction method with a multi-region mesh extraction scheme. The surface reconstruction algorithm is based on multi-level partition of unity implicit surfaces which we extended to the multi-material case. The mesh generation algorithm consists in a novel multidomain version of the marching tetrahedra. It generates multi-region meshes as a set of triangular surface patches consistently joining each other at material junctions. This paper presents this original meshing strategy, starting from boundary points extraction from the segmented data, to heterogeneous implicit surface definition, multi-region surface triangulation and mesh adaptation. Results indicate that the proposed approach produces smooth and high-quality triangular meshes with a reasonable geometric accuracy. Hence, the proposed method is well suited for subsequent volume mesh generation and Finite Element simulations. [less ▲] Detailed reference viewed: 74 (36 ULg) |
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