Rate dependent constitutive models are widely used in sheet metal forming and crash simulations. In these applications, the material is subjected to large deformations at strain rates of up to 1000/s. In addition, the stress state is seldom uniaxial and of multi-axial nature instead. It is the aim of this work to investigate the effect of stress state on the strain rate sensitivity of some BCC and FCC metals. The dynamic bulge testing cell for split Hopkinson pressure bar systems is used to perform high strain rate biaxial tensile tests on sheet metal. The original idea is to make use of the input bar to apply and measure the fluid pressure in the bulging experiment. Detailed finite element models of the testing systems are used to simulate all experiments and the parameters of the rate-dependent plasticity model are then identified through inverse analysis.