Papers by Author: Houman Borouchaki

Abstract: The compression characteristics of open-cell aluminum foams were experimentally and numerically investigated. It is found that the mechanical parameters, such as collapse stress and absorbed energy, are dependent on the porosity of aluminum foams. Three macroscopic models were chose to predict the compression behavior of open-cell foams. During simulation of metal foam compression, the finite elements distort severely at the local regions with high gradient of physical field such as stress, strain due to these problems. The procedure integrates Explicit solver of ABAQUS, OPTIFORM mesher and python script program transfer to execute step by step the incremental deformation process. At each step, the meshes are refined and coarsened automatically based on geometrical and physical error estimations; the physical fields are transferred from old to the new one using advanced algorithm.

Abstract: The compression characteristics of open-cell aluminum foams were experimentally and numerically investigated. It is found that the mechanical parameters, such as collapse stress and absorbed energy, are dependent on the porosity of aluminum foams material. During simulation of metal foam compression, the finite elements distort severely at the local regions with high gradient of physical field. The procedure integrates Explicit solver of Abaqus FEA, 3D Optiformmesher and Python script program transfer to execute step by step the incremental deformation of deformable body.

Abstract: Recently, new sheet metal forming technique, incremental forming has been introduced. It is based on using a single spherical tool, which is moved along CNC controlled tool path. During the incremental forming process, the sheet blank is fixed in sheet holder. The tool follows a certain tool path and progressively deforms the sheet. Nowadays, numerical simulations of metal forming are widely used by industry to predict the geometry of the part, stresses and strain during the forming process. Because incremental forming is a dieless process, it is perfectly suited for prototyping and small volume production [1, 2]. On the other hand, this process is very slow and therefore it can only be used when a slow series production is required. As the sheet incremental forming process is an emerging process which has a high industrial interest, scientific efforts are required in order to optimize the process and to increase the knowledge of this process through experimental studies and the development of accurate simulation models. In this paper, a comparison between numerical simulation and experimental results is realized in order to assess the suitability of the numerical model. The experimental investigation is realized using a three-axis CNC milling machine. The forming tool consists in a cylindrical rotating punch with a hemispherical head. A subroutine has been developed to describe the tool path from CAM procedure. A numerical model has been developed to simulate the sheet incremental forming process. The finite element code Abaqus explicit has been used. The simulation of the incremental forming process stays a complex task and the computation time is often prohibitive for many reasons. During this simulation, the blank is deformed by a sequence of small increments that requires many numerical increments to be performed. Moreover, the size of the tool diameter is generally very small compared to the size of the metal sheet and thus the contact zone between the tool and the sheet is limited. As the tool deforms almost every part of the sheet, small elements are required everywhere in the sheet resulting in a very high computation time. In this paper, an adaptive remeshing method has been used to simulate the incremental forming process. This strategy, based on adaptive refinement and coarsening procedures avoids having an initially fine mesh, resulting in an enormous computing time. Experiments have been carried out using aluminum alloy sheets. The final geometrical shape and the thickness profile have been measured and compared with the numerical results. These measurements have allowed validating the proposed numerical model. References [1] M. Yamashita, M. Grotoh, S.-Y. Atsumi, Numerical simulation of incremental forming of sheet metal, J. Processing Technology, No. 199 (2008), p. 163 172. [2] C. Henrard, A.M. Hbraken, A. Szekeres, J.R. Duflou, S. He, P. Van Houtte, Comparison of FEM Simulations for the Incremental Forming Process, Advanced Materials Research, 6-8 (2005), p. 533-542.

Abstract: As a material removal process, metal milling process involves large geometry deformation, material thermo-visco-plastic flow coupled with damage and complex contact-friction problems. During simulation of metal milling, the finite elements distort severely at the local regions with high gradient of physical field such as stress, strain and temperature due to these problems. This paper presents numerical adaptive remeshing procedure dedicated to metal milling process. The procedure integrates Explicit solver of ABAQUS, OPTIFORM mesher and python script program transfer to execute step by step the incremental milling process. At each step, the meshes are refined and coarsened automatically based on geometrical and physical error estimations; the physical fields are transferred (point to point) from old to the new one using advanced algorithm. Johnson-cook material model is used to simulate the material plastic flow with ductile damage. Some numerical results are given to demonstrate the efficiency of the proposed procedure.

Abstract: Simulations of Single Point Incremental Forming generally require a very high computation time because the tool path is long and small elements are required everywhere on the sheet. In this paper, a remeshing method based on refinement and coarsening strategies is used with abaqus/explicit to reduce the computational time. The simulation of a semi-spherical cup with a fine mesh is considered as a reference simulation. The remeshing method allows reducing the number of elements and therefore the CPU time during the simulations. A good prediction is observed with the remeshing method.

Abstract: Metal orthogonal cutting and blanking are two important forming processes which include material removing. During finite element analyzing, the nonlinear problems of boundary, material and geometry must be considered to obtain the accurate calculating results. In this paper, we present an advanced adaptive remeshing procedure which has the capacities to simulate material removing processes in three dimensions. The sizes of finite elements are well adapted to local conditions which have the high distributions of physical fields using priori and posteriori error estimates. Based on constraint Delaunay Kernel, the unit mesh strategy is proposed to improve the mesh quality. By optimizing of both mesh edges and mesh elements, the mesh shape qualities are strictly controlled as the regular tetrahedrons. In this paper, Johnson-cook model is considered to simulate the elastic-visco-plastical material behaviors. The damage initiation is also judged by Johnson-cook criterion. The finite elements which reach the criterion will be killed and the material removing processes finished step by step. The proposed adaptive remeshing scheme is well present using the simulation of metal orthogonal cutting, milling and blanking processes.

Abstract: Metal orthogonal cutting process involves complex geometry deformation and mate-rial characteristics as large thermal-visco-plastic ow include ductile damage. Simultaneously,the contact with friction occurs in the same zone. To build the nite element model for metalcutting, the nite element mesh will be severely distorted at the region with high gradientof stress/strain/temperature eld. In this paper, a Adaptive remeshing procedure which inte-grates the 3D OPTIFORM mesher, ABAQUS/Explicit solver and eld node-node eld transferalgorithm are proposed to solve these problems. The thermal-mechanical simulation for metalorthogonal cutting is realized to demonstrate our numerical simulation approach. Some simu-lation results are illustrated include continuous chip forming process, thermal-mechanical elddistribution and cutting force in di erent rank angles, cutting speeds and friction conditions.

Abstract: As soon as it is question of modelling the follow-up of a geometry during an operation of forming process, the difficulties of meshing and remeshing are often emphases. If the part is situated between rigid tools (case of the deep drawing), in the problems of remeshing are also added difficulties on the management of the contact between the parts. In this case, the deformations are caused by the contact with the tools whose geometry are fixed. The piece must take the shape of the tool geometries during the deformation. In this paper, we present a method coupling an adaptive remeshing strategy and a technique of projection on the tool. The remeshing is based on refinement and coarsening procedures. The projection of the new nodes on the tool allows keeping the contact between the part and the tools. Numerical examples show the efficiency of the method.

Abstract: In this work, an adaptive remeshing scheme is presented in order to simulate with accuracy sheet metal forming processes. During simulations of metal forming processes, large plastic deformations with ductile damage occur and severe mesh distortion takes place after a few incremental steps. Hence frequent remeshing of the part must be performed in order to carry out the finite element analysis. The necessary steps to remesh the damaged structure during the simulation of the sheet metal forming process are given. The adaptive remeshing based on refinement and coarsening techniques, is controlled by geometrical and physical size maps. This remeshing strategy has been coupled with a projection method in order to avoid problems of contact between the part and the rigid tools. The influence of the remeshing is studied on numerical examples which show the capacity of the proposed procedure.

Abstract: This paper presents an advanced numerical methodology which aims to improve virtually any metal forming processes. It is based on elastoplastic constitutive equations accounting for non-linear mixed isotropic and kinematic hardening “strongly” coupled with isotropic ductile damage. During simulation of metal forming processes, where large plastic deformations with ductile damage occur, severe mesh distorsion takes place after a finite number of incremental steps. Hence an automatic mesh generation with remeshing capabilities is essential to carry out the finite element analysis. Besides, when damage is taken into account a kill element procedure is needed to eliminate the fully damaged elements in order to simulate the growth of macroscopic cracks. The necessary steps to remesh a damaged structure in finite element simulation of forming processes including damage occurrence (initiation and growth) are given. An important part of this procedure is constituted by geometrical and physical error estimates. The meshing and remeshing procedures are automatic and are implemented in a computational finite element analysis package (ABAQUS/Explicit solver using the Vumat user subroutine). Some numerical results are presented to show the capability of the proposed procedure to predict the damage initiation and growth during the metal forming processes.