Abstract
A precise characterization of material behavior is necessary to identify yield criteria or hardening laws for an accurate numerical design of sheet metal forming processes. Current models like Yld2000-2d or Hill’48 do not consider the plane strain state, though this condition is primary cause of failure in deep drawing. It is anticipated that an improved yield locus contour which considers the stress under plane strain conditions leads to better results in numerical simulations of a deep drawing process. Within this contribution, a new experimental setup to characterize both principal stress components under plane strain as additional input data for material modelling is presented. Therefore, hydraulic bulge tests are carried out with a novel elliptical die, which implements a plane strain condition. Moreover, the improvement of the material model is investigated exemplarily for the three sheet metal alloys DC06, DP600 and AA5182. The resulting material parameters are used to identify the yield locus for plane strain by varying the yield locus exponent of Yld2000-2d. The results prove that considering plane strain yield locus results in a better sheet thickness distribution in comparison to conventional modelling of the deep drawing process.
Highlights
In many branches of industry, there is a trend towards a reduction of the overall weight through a lightweight construction concept
The yield criterion Yld2000-2d is enhanced by changing the yield locus exponent to a fit of the plane strain yield locus
The results in material modelling show a significant difference for the resulting yield locus exponent m and, the yield locus can only determine the first principal stress
Summary
In many branches of industry, there is a trend towards a reduction of the overall weight through a lightweight construction concept. Components made of conventional materials with a high sheet thickness are substituted by high-strength materials with a lower thickness and, a lower weight or materials with a lower relative density The challenge in this context is the lower formability of these materials. The stress state at plane strain is of crucial importance, since there is a low formability and a strong sheet thinning occurs even at low degrees of deformation [2]. A direct determination under plane strain conditions is not required for this model Both aspects, the lack of a direct determination of the flow stress in combination with the high error rate at plane strain implies an enormous potential for improving the mapping accuracy of numerical designed forming operations
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