Inverse parameter identification of an anisotropic plasticity model for sheet metal

Abstract

The increasing economic and ecological demands on the mobility sector require efforts to reduce resource consumption in both the production and utilization phases. The use of lightweight construction technologies can save material and increase energy efficiency during operation. Multi-material systems consisting of different materials and geometries are used to achieve weight reduction. Since conventional joining processes reach their limits in the connection of these components, new methods and technologies are necessary in order to be able to react versatilely to varying process and disturbance variables. For fundamental investigations of new possibilities in joining technology, numerical investigations are helpful to identify process parameters. To generate valid results, robust and efficient material models are developed which are adapted to the requirements of versatile joining technologies, for instance to the high plastic strains associated with self-piercing riveting. To describe the inherent strain-induced plastic orthotropy of sheet metal an anisotropic Hill-plasticity model is formulated. Tensile tests for different sheet orientations are conducted both experimentally and numerically to adjust the anisotropic material parameters by inverse parameter identification for aluminium EN AW-6014 and steel HCT590X. Then, the layer compression test is used to validate the model and the previously identified parameters.

Influence of plastic orthotropy on clinching of sheet metal

“…Thus, for ℋ 𝑠 = ℑ dev (deviatoric fourth order unit tensor), we recover isotropic von Mises plasticity. The tensor ℋ 𝑠 is set up from the Hill coefficients ℎ 𝛼𝛽 as described in [9,11].…”

“…Layer compression test. The layer compression test is an adaption of the conventional compression test based on DIN 50106 (see e. g. [9] for details and further literature). With this setup the plastic flow curve up to true plastic strains of about 0.7.…”

“…Tensile tests with different sheet orientations. Tensile tests were carried out in [9] according to DIN 6892-1. To investigate the anisotropy of the aluminium sheet metal, specimens were extracted under 0°, 45° and 90° to the rolling direction (RD) by laser cutting.…”

“…Firstly, from the tensile test the r-values 𝑟 𝜃 can be determined from the strains measured by an optical measuring system. These were evaluated at an elongation of 10 mm (20% strain), compare [9], and are reiterated in Table 1. Moreover, it is possible to compute the average or normal anisotropy 𝑟 n from these rvalues [14] as…”

“…We focus on an aluminium alloy EN AW-6014 T4 with sheet thickness 2 mm. Its plastic orthotropy has already been characterised in [9] by tensile tests and layer compression testsbeing more pronounced than for a dual-phase steel HCT590X. Moreover, in contrast to the steel, the biaxial r-value of the aluminium alloy was less than 1, possibly rendering a different behaviour.…”