Identification of sheet metal hardening for large strains with an in-plane biaxial tensile test and a dedicated cross specimen

Abstract

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

Characterization of anisotropic yield surfaces for titanium sheet using hydrostatic bulging with elliptical dies

“…(S. Zhang, Leotoing, Guines, Thuillier, & Zang, 2014) used a biaxial test to 3 generate data to calibrate an anisotropic yield function for AA5086 to about 12% major strain. Some of the highest levels of strain achieved using cruciform specimens have been reported by (Liu, Guines, Leotoing, & Ragneau, 2015) for an AA5086 alloy. In this case, about 16% major strain was measured corresponding to an effective (von Mises) strain of 32%.…”

Identification of strain rate-dependent mechanical behaviour of DP600 under in-plane biaxial loadings

“…Nevertheless, only uniaxial stress and strain states and relatively low strain levels, compared to the ones obtained in forming operations, can be reached. In order to obtain information concerning multiaxial loading conditions encountered in sheet forming processes, several tests have been developed such as, tension tests on wide specimens [1,2], combined plane strain-simple shear test on only one specimen [3,4], hydraulic bulge tests with circular or elliptical die openings [5], combined uniaxial tension-internal pressure tests [6], Marciniak [7] or Nakazima stamping tests [8] and biaxial tensile tests on flat cruciform specimen [9,10]. As shown in these last works, the biaxial tensile test on a flat cruciform specimen presents several advantages: it is a frictionless test, it allows to reach large plastic strains and linear and non-linear strain paths can be easily achieved.…”

“…Recently, a specific dynamic biaxial tensile device with four independent servo-hydraulic actuators (each one with a loading capacity of 50kN) has been developed in the Laboratory of Civil and Mechanical Engineering (LGCGM) of National Institute of Applied Sciences (INSA) at Rennes [24]. This biaxial tensile machine has been used to lead in-plane biaxial tensile tests on cruciform specimens at quasi-static strain rate for different applications: (i) calibration of yield criteria [25], (ii) identification of hardening laws at large strains [10] and (iii) determination of forming limit curves [9] of metallic sheets. Depending on applications, several in-plane specimen shapes have been proposed and validated and linear or non-linear strain paths can be imposed.…”

“…On flat cruciform specimen, Zhang [25] used discrete values of principal strains along a diagonal direction of the central zone of a cruciform specimen. With a more complex cross specimen shape, Liu [10] used local strain measures in the specimen centre to identify hardening law of a 5086 aluminium alloy up to large strains. Due to the increasing acquisition frame rate of cameras, these non-contact techniques are now well adapted to dynamic characterizations and may be used for homogeneous or non-homogeneous tests.…”

“…Based on these observations, two phenomenological ratedependent hardening models are selected and calibrated. Then, static and dynamic equi-biaxial tests are performed on a dedicated cross specimen shape, previously developed and validated for quasi-5 static applications [10], up to an equivalent plastic strain of 30%. Parameters of the two ratedependent hardening formulations are identified from biaxial experiments by means of an optimization procedure minimizing the difference between local simulated and experimental strains in the specimen centre.…”