Simulation of hydro-formability testing for tubes

With the development of dedicated tubular products for hydroforming, the need for a representative test for these products evolves. Currently free expansion tests are used, but these tests only follow a more or less plane strain deformation. In reality, hydroforming is used with end feeding and the plane strain deformation is not representative. By performing a number of tests with different positive and negative end feeding a forming limit curve can be constructed, dedicated to tubular hydroforming. In the paper simulations are presented for the tests with different end feeding conditions, using shell elements. The influence of material parameters is investigated. Results of the FEM analysis are comparable with results from a Marciniak–Kuczynksi analysis. Some salient differences can be attributed to the more realistic incorporation of boundary conditions in the FEM analysis. In the tensile/compression region, the M–K analysis requires a free displacement perpendicular to the main principal strain to have a neck developed at a specific angle to the loading direction. In a hydroforming test the lateral displacement of the sheet would result in a rotation along the tube axis, which is prevented by the seals. The constraint displacement results in a higher forming limit