Abstract
Warm forming is widely used as increasing the temperature is a solution to improve the formability of aluminum alloys. The stress (or strain) state is one of the most important factors affecting the formability of metals. In warm forming, the temperature and strain rate also play an important role on the deformation and fracture behavior. Figuring out the relationship between formability, temperature, strain rate and stress state is of great importance for providing more understanding of ductile fracture in warm forming conditions. Therefore, the objective of this work is to investigate the influence of temperature on the ductile fracture of a 6000 series aluminum alloy sheet metal under different stress states. Dogbone specimens, notched tensile specimens with different radius, tensile specimens with a central hole and shear specimens are used to cover a wide range of stress states. The hybrid experimental-numerical approach is used to identify the fracture strain and the corresponding stress state parameters (i.e. stress triaxiality and Lode parameter). To this end, fracture tests are carried out at 200°C using a tensile machine to determine the instant of fracture. Numerical simulations of the tensile tests are performed in 3D with the finite element code Abaqus to predict the strain field and calculate the evolution of the stress state. To accurately model the material behavior the positive strain rate sensitivity in the flow stress response at elevated temperature is considered. The results show a strong dependency of the ductile fracture on the temperature, strain rate and stress state.
Highlights
Light materials are increasingly used in automotive industry to satisfy the growing demand for higher fuel efficiency and lower environmental impact
There is no significant difference in stress-strain curves along different loading directions indicating isotropic properties with respect to strength and strain hardening
The stress state dependent facture behavior of AA6061-T6 aluminum alloy is investigated at 200°C
Summary
Light materials are increasingly used in automotive industry to satisfy the growing demand for higher fuel efficiency and lower environmental impact. It is well known that the stress state is one of the most important factors affecting the formability of metals. Bao and Wierzbicki [1] evidenced, via a series of tests on 2024-T351 aluminum alloy, the strong influence of the stress triaxiality on the ductility. Zhang et al [3] found that besides stress triaxiality the Lode parameter related to the third invariant of the deviatoric stress tensor has an influence on the ductile fracture of metallic materials. They claimed that the use of the Lode parameter, with stress triaxiality, gives a complete description of the stress state
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