Experimental and numerical investigation of a strain rate controlled hydraulic bulge test of sheet metal

An exact characterization of the material behavior is required to identify material laws, e.g. yield criteria or isotropic hardening laws, for an accurate numerical design of forming operations. For instance, the hydraulic bulge test is carried out to determine the material behavior under biaxial stretching. In case of strain rate sensitive materials, as aluminum alloys or mild steels, the influence of the strain rate is important and a constant strain rate during the test is necessary for reliable results. In this contribution, a hydraulic bulge test setup is presented, which allows an online detection of the local strain to control the hydraulic pressure for an almost constant strain rate during the test. Moreover, the difference of the material behavior between strain rate controlled bulge tests and bulge tests with commonly used constant hydraulic cylinder speed is investigated for the aluminum alloy AA5182-O, the deep drawing steel DX54 and the advanced high strength steel HCT980X. Additionally, the influence of the hardening behavior on the numerical results of the hydraulic bulge test is exemplarily investigated for AA5182-O.