Abstract
It is now well recognized that the material data obtained from a tensile test is less appropriate than those from a Tube Bulging Test (TBT) for a finite element simulation of tube hydroforming. However, the manufacturers still use classical data (often tensile test data) for designing metal operations due to the lack of standard for the TBT and a more complex post processing analysis of experimental measures. Getting the hardening curve from the tube bulging test requires the use of an analytical or numerical model. In this paper, three models for post-processing measures obtained from the TBT are compared based on the same experimental procedure. Thanks to a preliminary step, consisting of the validation of the analytical models through the use of finite element simulations of the TBT, it highlights that the results obtained for the local (stress and strain) and global components (the thickness distribution along the tube and the deformed tube profile) are very close, whatever the models. The test configuration (die radius and free length) seems to have no significant impact on the resulting stress-strain curve for the three models. The three models are used for post processing tube bulging tests performed on AISI304, INCONEL and Copper tubes validating their capacity for tube characterization on different materials. Finally, this study demonstrates that the Boudeau-Malecot Model can be used to obtain hardening curve from TBT without a loss of accuracy compared to more complex post-processing models and with an important gain of quality compared to tensile test.
Highlights
Tube hydroforming process consists of forming a tube inside a closed and shaped cavity by applying an internal pressure
In order to control the influence of the geometrical characteristics of the tube bulging test on the tube material characterization on one hand, and to evaluate the three selected models for post-processing the experimental results in the other, it is proposed to base the analyses on results obtained with finite element simulations
Their programming is validated based on postprocessing pressure – bulge height data obtained by finite element (FE) simulations of the tube bulging test
Summary
Tube hydroforming process consists of forming a tube inside a closed and shaped cavity by applying an internal pressure. The internal pressure is most of the time combined to a compression axial force, to produce complex shapes and to minimize the critical thinning. This technology is of particular interest for industry because it allows the achievement of complex hollow shaped parts with a reduced number of welding spots and a higher structural quality. The axial compressive force – internal pressure path must be optimised to avoid bursting, wrinkling and buckling by using the Process Window Diagram [2]. That is why the tube bulging test has been developed, where a tube is freely expanded by applying an internal pressure (Fig. 1)
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