The use of sheet metal forming processes can be limited by the formability of materials, especial... more The use of sheet metal forming processes can be limited by the formability of materials, especially in the case of aluminium alloys. To improve the formability, warm forming processes can be considered. In this work, the effects of temperature and strain rate on the formability of a given aluminium alloy (AA5086) have been studied by means of both experimental and predictive approaches. Experimental tests have been carried out with a Marciniak stamping experimental device. Forming limit curves (FLCs) have been established on a temperature range going from ambient temperature to 200°C and on a strain rate range going from quasi-static up to 2s-1. In order to predict the experimental temperature and strain rate sensitivities, a predictive model based on the finite element simulation of the classical Marciniak and Kuczynski (M-K) geometrical model is proposed. The limit strains obtained with this model are very sensitive to the thermo-viscoplastic behaviour modeling and to the calibrat...
Accurate assessment of the sheet formability incorporating the operating conditions (temperature ... more Accurate assessment of the sheet formability incorporating the operating conditions (temperature and strain rate) encountered during a forming process enables more reliable results from the numerical simulation process. The warm sheet forming technique can increase the formability greatly and it should be taken into account when developing predictive tools of FLC (Forming Limit Curves). The development of a simple Marciniak and Kuczynski (M-K) model, based on a Finite Element formulation, has highlighted the influence of mechanical behavior identified for an aluminium alloy 5086 on the determination of FLC.
In the present work, the formability of an aluminium alloy (AA5083) sheet at elevated temperature... more In the present work, the formability of an aluminium alloy (AA5083) sheet at elevated temperature (240±C and 300±C) is investigated by theoretical and numerical approaches, using the Swift hardening law. For the theoretical one, an algorithm based on Newton-Raphson method is developed to calculate the limit strains in the frame of the M-K (Marciniak-Kuczynski) model. Numerically, the M-K model is simulated with the commercially available finite-element code ABAQUS. The comparison between the theoretical and numerical evaluation of FLCs shows a good agreement between two approaches. Finally, the effect of strain rate sensitivity index (m) and forming speed on formability is analyzed. Results reveal that the formability is an increasing function of m while there is no significant influence of forming speed on the sheet formability.
Composite materials are widely used in engineering applications. The mechanical characterization ... more Composite materials are widely used in engineering applications. The mechanical characterization of these materials is of major importance and the in-plane biaxial tensile test can be an interesting alternative to conventional uniaxial tensile tests along multiple directions. The major problem related to this test is the design of the cruciform specimen. In this study, the objective lies in the failure characterization of composite materials under a wide range of stress state. The proposed specimen is composed of two aluminum tabs glued on each side of a constant thickness composite sample. Experimental biaxial tensile tests are led for several displacement loading ratios from uniaxial to equibiaxial stretching. Major and minor strains in the central zone (calculated by DIC technic) and measured tensile forces along the two specimen axes constitute the experimental database. According to the loading ratios, the minor and major stresses (or strains) at the onset of failure will defin...
This paper investigates the thermomechanical behavior of Al-Mg alloys submitted to biaxial loadin... more This paper investigates the thermomechanical behavior of Al-Mg alloys submitted to biaxial loading until fracture. The study aims to characterize calorimetric signature accompanying the formation and propagation of Portevin-Le Chatelier (PLC) bands induced by such a loading condition. Full kinematic and thermal fields on the specimen surface were characterized by using Digital Image Correlation (DIC) and infrared thermography (IRT). Heat source field was reconstructed from the temperature field and the heat diffusion equation. The heat source map enables us to visualize spatio-temporal gradients in the calorimetric response of the material and to investigate the kinematics of PLC bands induced by equibiaxial tensile loading. Under certain conditions, heat source maps can be seen as mechanical dissipation maps. At the specimen centre, the heat source exhibits jumps that fit with jumps of temperature and equivalent deformation rate.
La mise en forme de toles metalliques met en jeu des phenomenes complexes qui dependent de nombre... more La mise en forme de toles metalliques met en jeu des phenomenes complexes qui dependent de nombreux parametres comme la geometrie des outils, leur temperature, leur vitesse, … . La simulation numerique est donc un outil interessant facilitant l’optimisation des gammes de fabrication par la realisation d’etudes parametriques plus rapides et moins couteuses. Neanmoins, le recours a la simulation numerique necessite une connaissance precise du comportement elasto-viscoplastique des materiaux constituant les toles metalliques, comportement generalement determine a partir d’essais de traction uniaxiaux. Or, pendant une operation de mise en forme, les toles sont le plus souvent soumises a des sollicitations biaxiales qui conduisent de plus a des niveaux de deformation bien superieurs a ceux atteints lors d’un simple essai de traction. De plus, suivant le procede considere, des vitesses de deformation dites « intermediaires » peuvent etre atteintes (de l’ordre de quelques dizaines de s-1)....
In this paper, a new coupling approach Process/Machine applied to Robotized Single Point Incremen... more In this paper, a new coupling approach Process/Machine applied to Robotized Single Point Incremental Forming (RSPIF) is presented. This approach consists in coupling a Finite Element Analysis (FEA) of the process with an elasto-geometrical modeling of the robot to improve the geometrical accuracy of the trajectory. The FEA, assuming a rigid structure, is first used to evaluate the forces at the interface be-tween the tool and the sheet during the forming stage. These forces are then intro-duced as input data of the elasto-geometrical model of the robot, to predict the tool path deviations and to correct the trajectory. In order to make efficient the tool path correction, the weight of three numerical and material parameters of the FEA on the predicted forces is investigated. Finally, the efficiency of the proposed method is vali-dated by the comparison of the numerical and experimental geometries obtained with or without correction of the tool path.
The aim of this study is to investigate the capabilities of a new forming process named "spr... more The aim of this study is to investigate the capabilities of a new forming process named "springback forming" of stiffened panels. In order to reduce the manufacturing costs, it’s necessary to realize the maximum of assembly operations in a flat-position. The basic idea is to apply a tension on the stiffeners before assembling them with the plate. The forming stage is achieved when releasing the stiffeners tension. The capabilities of this process have been studied using both a numerical finite element and an analytical approaches. A parametric analysis has been performed in order the influence of different parameters on the final shape. Finally, this new process is extended to the forming of double-curved panels. Mots-clefs : Mise en forme ; structures raidies ; retour elastique
Abstract The in-plane biaxial tensile test with a new cruciform specimen is used to investigate t... more Abstract The in-plane biaxial tensile test with a new cruciform specimen is used to investigate the forming limit strains at fracture of DP600 sheet metal. The experimental forming limits are determined under linear and non-linear strain paths without unloading provided by four independent dynamic actuators. The Oyane ductile fracture criterion is used to predict the experimental results under different strain paths.
The accuracy of simulation result depends greatly on the implemented hardening law. An appropriat... more The accuracy of simulation result depends greatly on the implemented hardening law. An appropriate hardening model should be able to describe the coupling effects of the strain, strain rate and temperature on the flow stress of the material. Based on the stress-strain curves obtained from uniaxial tensile tests, two different types of hardening models (power law and saturation) are proposed to describe the flow stresses of an aluminum alloy AA5086 under different temperatures (20, 150 and 200°C) and tensile speeds (1, 10 and 100 mm·s-1). The correlation results are compared to experimental data and the roles of the hardening models in predicting the material flow stress are compared and discussed.
In this paper, a new coupling approach Process/Machine applied to Robotized Single Point Incremen... more In this paper, a new coupling approach Process/Machine applied to Robotized Single Point Incremental Forming (RSPIF) is presented. This approach consists in coupling a Finite Element Analysis (FEA) of the process with an elasto-geometrical modeling of the robot to improve the geometrical accuracy of the trajectory. The FEA, assuming a rigid structure, is first used to evaluate the forces at the interface be-tween the tool and the sheet during the forming stage. These forces are then intro-duced as input data of the elasto-geometrical model of the robot, to predict the tool path deviations and to correct the trajectory. In order to make efficient the tool path correction, the weight of three numerical and material parameters of the FEA on the predicted forces is investigated. Finally, the efficiency of the proposed method is vali-dated by the comparison of the numerical and experimental geometries obtained with or without correction of the tool path.
The use of sheet metal forming processes can be limited by the formability of materials, especial... more The use of sheet metal forming processes can be limited by the formability of materials, especially in the case of aluminium alloys. To improve the formability, warm forming processes can be considered. In this work, the effects of temperature and strain rate on the formability of a given aluminium alloy (AA5086) have been studied by means of both experimental and predictive approaches. Experimental tests have been carried out with a Marciniak stamping experimental device. Forming limit curves (FLCs) have been established on a temperature range going from ambient temperature to 200°C and on a strain rate range going from quasi-static up to 2s-1. In order to predict the experimental temperature and strain rate sensitivities, a predictive model based on the finite element simulation of the classical Marciniak and Kuczynski (M-K) geometrical model is proposed. The limit strains obtained with this model are very sensitive to the thermo-viscoplastic behaviour modeling and to the calibrat...
Accurate assessment of the sheet formability incorporating the operating conditions (temperature ... more Accurate assessment of the sheet formability incorporating the operating conditions (temperature and strain rate) encountered during a forming process enables more reliable results from the numerical simulation process. The warm sheet forming technique can increase the formability greatly and it should be taken into account when developing predictive tools of FLC (Forming Limit Curves). The development of a simple Marciniak and Kuczynski (M-K) model, based on a Finite Element formulation, has highlighted the influence of mechanical behavior identified for an aluminium alloy 5086 on the determination of FLC.
In the present work, the formability of an aluminium alloy (AA5083) sheet at elevated temperature... more In the present work, the formability of an aluminium alloy (AA5083) sheet at elevated temperature (240±C and 300±C) is investigated by theoretical and numerical approaches, using the Swift hardening law. For the theoretical one, an algorithm based on Newton-Raphson method is developed to calculate the limit strains in the frame of the M-K (Marciniak-Kuczynski) model. Numerically, the M-K model is simulated with the commercially available finite-element code ABAQUS. The comparison between the theoretical and numerical evaluation of FLCs shows a good agreement between two approaches. Finally, the effect of strain rate sensitivity index (m) and forming speed on formability is analyzed. Results reveal that the formability is an increasing function of m while there is no significant influence of forming speed on the sheet formability.
Composite materials are widely used in engineering applications. The mechanical characterization ... more Composite materials are widely used in engineering applications. The mechanical characterization of these materials is of major importance and the in-plane biaxial tensile test can be an interesting alternative to conventional uniaxial tensile tests along multiple directions. The major problem related to this test is the design of the cruciform specimen. In this study, the objective lies in the failure characterization of composite materials under a wide range of stress state. The proposed specimen is composed of two aluminum tabs glued on each side of a constant thickness composite sample. Experimental biaxial tensile tests are led for several displacement loading ratios from uniaxial to equibiaxial stretching. Major and minor strains in the central zone (calculated by DIC technic) and measured tensile forces along the two specimen axes constitute the experimental database. According to the loading ratios, the minor and major stresses (or strains) at the onset of failure will defin...
This paper investigates the thermomechanical behavior of Al-Mg alloys submitted to biaxial loadin... more This paper investigates the thermomechanical behavior of Al-Mg alloys submitted to biaxial loading until fracture. The study aims to characterize calorimetric signature accompanying the formation and propagation of Portevin-Le Chatelier (PLC) bands induced by such a loading condition. Full kinematic and thermal fields on the specimen surface were characterized by using Digital Image Correlation (DIC) and infrared thermography (IRT). Heat source field was reconstructed from the temperature field and the heat diffusion equation. The heat source map enables us to visualize spatio-temporal gradients in the calorimetric response of the material and to investigate the kinematics of PLC bands induced by equibiaxial tensile loading. Under certain conditions, heat source maps can be seen as mechanical dissipation maps. At the specimen centre, the heat source exhibits jumps that fit with jumps of temperature and equivalent deformation rate.
La mise en forme de toles metalliques met en jeu des phenomenes complexes qui dependent de nombre... more La mise en forme de toles metalliques met en jeu des phenomenes complexes qui dependent de nombreux parametres comme la geometrie des outils, leur temperature, leur vitesse, … . La simulation numerique est donc un outil interessant facilitant l’optimisation des gammes de fabrication par la realisation d’etudes parametriques plus rapides et moins couteuses. Neanmoins, le recours a la simulation numerique necessite une connaissance precise du comportement elasto-viscoplastique des materiaux constituant les toles metalliques, comportement generalement determine a partir d’essais de traction uniaxiaux. Or, pendant une operation de mise en forme, les toles sont le plus souvent soumises a des sollicitations biaxiales qui conduisent de plus a des niveaux de deformation bien superieurs a ceux atteints lors d’un simple essai de traction. De plus, suivant le procede considere, des vitesses de deformation dites « intermediaires » peuvent etre atteintes (de l’ordre de quelques dizaines de s-1)....
In this paper, a new coupling approach Process/Machine applied to Robotized Single Point Incremen... more In this paper, a new coupling approach Process/Machine applied to Robotized Single Point Incremental Forming (RSPIF) is presented. This approach consists in coupling a Finite Element Analysis (FEA) of the process with an elasto-geometrical modeling of the robot to improve the geometrical accuracy of the trajectory. The FEA, assuming a rigid structure, is first used to evaluate the forces at the interface be-tween the tool and the sheet during the forming stage. These forces are then intro-duced as input data of the elasto-geometrical model of the robot, to predict the tool path deviations and to correct the trajectory. In order to make efficient the tool path correction, the weight of three numerical and material parameters of the FEA on the predicted forces is investigated. Finally, the efficiency of the proposed method is vali-dated by the comparison of the numerical and experimental geometries obtained with or without correction of the tool path.
The aim of this study is to investigate the capabilities of a new forming process named "spr... more The aim of this study is to investigate the capabilities of a new forming process named "springback forming" of stiffened panels. In order to reduce the manufacturing costs, it’s necessary to realize the maximum of assembly operations in a flat-position. The basic idea is to apply a tension on the stiffeners before assembling them with the plate. The forming stage is achieved when releasing the stiffeners tension. The capabilities of this process have been studied using both a numerical finite element and an analytical approaches. A parametric analysis has been performed in order the influence of different parameters on the final shape. Finally, this new process is extended to the forming of double-curved panels. Mots-clefs : Mise en forme ; structures raidies ; retour elastique
Abstract The in-plane biaxial tensile test with a new cruciform specimen is used to investigate t... more Abstract The in-plane biaxial tensile test with a new cruciform specimen is used to investigate the forming limit strains at fracture of DP600 sheet metal. The experimental forming limits are determined under linear and non-linear strain paths without unloading provided by four independent dynamic actuators. The Oyane ductile fracture criterion is used to predict the experimental results under different strain paths.
The accuracy of simulation result depends greatly on the implemented hardening law. An appropriat... more The accuracy of simulation result depends greatly on the implemented hardening law. An appropriate hardening model should be able to describe the coupling effects of the strain, strain rate and temperature on the flow stress of the material. Based on the stress-strain curves obtained from uniaxial tensile tests, two different types of hardening models (power law and saturation) are proposed to describe the flow stresses of an aluminum alloy AA5086 under different temperatures (20, 150 and 200°C) and tensile speeds (1, 10 and 100 mm·s-1). The correlation results are compared to experimental data and the roles of the hardening models in predicting the material flow stress are compared and discussed.
In this paper, a new coupling approach Process/Machine applied to Robotized Single Point Incremen... more In this paper, a new coupling approach Process/Machine applied to Robotized Single Point Incremental Forming (RSPIF) is presented. This approach consists in coupling a Finite Element Analysis (FEA) of the process with an elasto-geometrical modeling of the robot to improve the geometrical accuracy of the trajectory. The FEA, assuming a rigid structure, is first used to evaluate the forces at the interface be-tween the tool and the sheet during the forming stage. These forces are then intro-duced as input data of the elasto-geometrical model of the robot, to predict the tool path deviations and to correct the trajectory. In order to make efficient the tool path correction, the weight of three numerical and material parameters of the FEA on the predicted forces is investigated. Finally, the efficiency of the proposed method is vali-dated by the comparison of the numerical and experimental geometries obtained with or without correction of the tool path.
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Papers by Dominique Guines