The aim of this work is to compare different biaxial specimen geometries and loading conditions concerning their applicability as experimental database for an inverse finite element model updating procedure to identify the material parameters of sheet steel. Therefore, the deformation of the specimens is recorded with an optical, three‐dimensional full‐field deformation measurement system, and the utilised displacement data at the surface of the specimens are calculated via digital image correlation.
The numerical material model for the simulations is based on a three‐dimensional, anisotropic elasto‐plastic ansatz and is implemented into a commercial finite element software code. The material parameters that are identified with the different specimen geometries are the hardening variables and the anisotropic plastic values. Based on the identification results, a selection criterion for the evaluation of specimen geometries for the inverse parameter identification is presented.
a b s t r a c tDetailed experimental data on the behavior of textured sheet metals under compressive loading is important to describe their tension-compression asymmetry. This is particularly needed for materials that exhibit a strength-differential effect, or in cases where the Bauschinger effect occurs. So far, there is no systematic work describing the third quadrant in the 2D stress space under biaxial compressive loading. This paper presents a new device for biaxial, compressive in-plane testing of thin sheets. Biaxial and uniaxial compression experiments are carried out in the strain controlled device, analyzing the behavior of deep drawing steel sheets with and without skin-pass treatment. Moreover, in order to allow for the experimental description of the yield surfaces, biaxial tensile tests are performed. Detailed numerical validations and experimental strain analysis both for the new specimen for biaxial compressive testing and for the cruciform specimen for biaxial tensile testing show that reasonably homogeneous strain distributions can be achieved. The combined experimental and numerical method presented here allows to evaluate the tension-compression asymmetry of thin sheet materials. The results for the skin-passed condition clearly exhibit a tension-compression asymmetry, which highlights the necessity of biaxial compression tests already in the as-received material condition. The biaxial compression test opens a pathway to a more detailed analysis of the flow behavior of thin sheets under biaxial compression loading.
Sheet-bulk-metal forming processes require an accurate material model which is derived in this contribution. The microscopic model is based on a simulation of a real microstructure. A validation on the macroscopical scale is performed through the reproduction of the experimentally calculated yield surface based on the homogenised structural response of a corresponding deformed representative volume element (RVE). The microstructural material model is also compared with a macroscopical phenomenological model based on logarithmic strains. The homogenised microscopic model and the phenomenological macroscopic model are in good agreement with the evolution of the stresses and strains obtained during the experiments.
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