The main objective of this work is to propose a new experimental device able to give for a single specimen a good prediction of rheological parameters and formability under static and dynamic conditions (for intermediate strain rates). In this paper, we focus on the characterization of sheet metal forming. The proposed device is a servo-hydraulic testing machine provided with four independent dynamic actuators allowing biaxial tensile tests on cruciform specimens. The formability is evaluated thanks to the classical forming limit diagram (FLD), and one of the difficulties of this study was the design of a dedicated specimen for which the necking phenomenon appears in its central zone. If necking is located in the central zone of the specimen, then the speed ratio between the two axes controls the strain path in this zone and a whole forming limit curve can be covered. Such a specimen is proposed through a numerical and experimental validation procedure. A rigorous procedure for the detection of numerical and experimental forming strains is also presented. Finally, an experimental forming limit curve is determined and validated for an aluminium alloy dedicated to the sheet forming processes (AA5086).

International audienceIn this work, an in-plane biaxial tensile test of cruciform specimen is performed to identify the hardening behaviour of metallic sheets under large strains. Firstly, an optimal shape of the specimen is suggested. Then, a biaxial tensile test is carried out for an aluminium alloy AA5086. Experimental forces on the two axes of the specimen are measured during the test and strains in the central area of the specimen are post-treated by means of Digital Image Correlation (DIC) technique. Finally, by considering different yield criteria, the associated hardening laws are identified thanks to an inverse procedure based on a Finite Element (FE) modeling of the biaxial tensile test and on the experimental data mentioned above. The identified biaxial flow curves are then compared with the ones from the classical uniaxial tensile test

In this paper, a coupling methodology is involved and improved to correct the tool path deviations induced by the compliance of industrial robots during an incremental sheet forming task. For that purpose, a robust and systematic method is rst proposed to derive the elastic model of their structure and an ef cient FE simulation of the process is then used to predict accurately the forming forces. Their values are then de ned as the inputs of the proposed elastic model to calculate the robot TCP pose errors induced by the elastic deformations. This avoid thus a rst step of measurement of the forces required to form a test part with a stiff machine. An intensive experimental investigation is performed by forming a classical frustum cone and a non-symetrical twisted pyramid. It validates the robustness of both the FE analysis and the proposed elastic modeling allowing the nal geometry of the formed parts to converge towards their nominal speci cations in a context of prototyping applications.

International audienceWith the application of new forming techniques (hydroforming, incremental forming), it is necessary to improve the characterization of the formability of materials and in particular the influence of strain rate. This paper begins with the characterization of material behavior of an aluminum alloy 5083 at high temperatures. To describe its visco-plastic behavior, Swift's hardening law is used and the corresponding parameter values are identified. Then, two different approaches are introduced to construct FLDs (forming limit diagrams) of this alloy sheet and evaluate the effect of the rate sensitivity index on its formability. The first one is theoretical (the M-K model), and an algorithm is developed to calculate the limit strains by this model. In the second approach, the Marciniak test is simulated with the commercially available finite-element program ABAQUS. Based on FEM results, different failure criteria are discussed and an appropriate one is chosen to determine the onset of localized necking. With the material behavior data corresponding to AA5083 at 150 ◦C, parametric studies are carried out to evaluate the effect of the strain rate sensitivity index. The comparison of results by these two approaches shows the same tendency that an improvement of the formability with increasing strain rate sensitivity is observed. Finally, by consideration of the compensating effects of the strain hardening and rate sensitivity indices, the FLDs of this sheet at 150, 240 and 300 ◦C are determined and compared. Results showthat the formability of AA5083 seems not to be improved up to a certain temperature (between 240 and 300 ◦C), above this temperature, the formability is greatly enhanced

International audienceBron and Besson yield criterion has been used to model the plastic anisotropic behavior of an aluminum alloy series 5000. The parameters of this anisotropic yield model have been identified by two different methods: a classical one, considering several homogeneous conventional experiments and an exploratory one, with only one biaxial test. On one hand, the parameter identification with conventional experiments has been carried out with uniaxial tensile and simple shear tests in different orientations to the rolling direction and with a hydraulic bulge test, all of them considered at three equivalent plastic strain levels. On the other hand, Bron and Besson yield function has also been calibrated with inverse analysis from only a cross biaxial tensile test, since it was shown that the strain distribution in the center of the cruciform specimen is significantly dependent on the yield criterion. The principal strains along a specified path in the gauge area of the cruciform specimen have been analyzed and the gap between experimental and numerical values was minimized. Finally the yield contours obtained with the two methods have been compared and discussed