Analysis of the Hydraulic Bulge Test with FEA Concerning the Accuracy of the Determined Flow Curves

Abstract

This work covers the finite element analysis of geometric and process parameters in hydraulic bulge tests in terms of the accuracy of the evaluated flow curve. The important parameters are identified and varied to cover the whole range of possible uses. The effects of these parameters are analyzed for three representative materials: aluminium, mid-strength steel, and high-strength steel. The flow curves of the materials for each set of parameters are calculated by using the results of the simulations and the membrane theory. It is seen that even with simulation results, it is not always possible to obtain the input flow curve, especially towards the end of the test. The dimensions of the sheet and the tooling affect the plastic strain development and geometry of the bulge, leading to errors in computed flow curves. In order to observe the effect of the material flow from the flange on the determined yield stresses, the function and position of the drawbeads are also examined. These parameters, together with the method used to calculate the radius of the bulge, determine the accuracy of the calculated flow curve. Guidelines for an accurate flow curve determination regarding the test set-up and calculation methods are given.

Accurate determination of flow curves using the bulge test with optical measuring systems

“…They varied the work hardening coefficient (n-value) and the strain ratio (r-value) but always within the context of planar isotropy. Güner et al (2009) investigated the influence of geometrical dimensions (aperture radius, die shoulder radius) for three different materials on the accuracy of the determined flow curves. One of the conclusions is that the sphere fit of the surface introduces a systematic error and other mathematical equations should be considered.…”