Papers by Author: Abel Cherouat

Abstract: Hemp fibres are using as reinforcement for compounds based on polymer in different industrial manufacturing (aerospace and automotive) for their interesting mechanical and ecological properties. The hemp fibres present a non-constant cross section and complex geometry that can have a high effect on their mechanical properties. In this study, a micro-traction test coupled with a numerical imaging treatment and a finite elements method are used. The mechanical tensile test allows to determinate the evolution of the traction load in function of the displacement until the fibre crack. The used fiber are incorporate in plastic material is order to obtained PP/hemp reinforcement composite part. Static and dynamic tests are proposed in order to study trhe behaviour of green material subjected to tensile load.

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: In this paper, a new procedure for the identification of constitutive elastoplastic models coupled with an isotropic damage variable under large strains is presented. It is a statistical approach used for experimental characterization and identification based on a design of experiments of numerical simulations of mechanical characterization tests. The parameters for a reference material are determined by multiple linear regression as a function of shape indices.The material of reference is mild steel E24; it was characterized in a series of tensile tests of thin plate specimens. The Swift hardening law coupled with an isotropic damage variable that was identified by introducing in the established formulations shape indexes extracted from the experimental tension/elongation curves.The number of simulations required for the identification of the parameters of the reference material is roughly 18% of the number required by the inverse method (simplex).

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: The hemp fibres present specific fibre morphology and a complex non homogeneous cross section which changes in function of the location along the fibre length. Thus the mechanical properties of hemp fibres request a specific characterization method. In this study, firstly, a digital treatment method was developed allowing to consider different geometrical modelling methods: homogeneous or non-homogenous cross section, average global cross section, and cross section measured at the rupture location, including a 3D CAD model reconstruction of the fibre.

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: This study presents experimental and numerical approaches to study the thermo-elasto-plastic behavior coupled to ductile damage of thin sheet. The study highlights the influence of temperature on the mechanical properties affecting the ability of forming aluminum sheet 1050A. The properties of the Swifts model hardening coupled to isotropic ductile damage variable and the Erichsen Index are obtained using inverse approach (Nelder-Mead method). The obtained results have established a correlation between the Index Erichsen formability of the material.

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.