Uniaxial quasi-static tests and dynamic compression tests at high strain rates have been performed to determine the mechanical behaviour of sheet metals widely used in the automotive industry. The quality of experimental data at high strain rates obtained with a split Hopkinson pressure bar (SHPB) depended on signals processing. Improvements in this field are discussed: the wave dispersion correction, an exact delay setting in the shifting of the waves and the use of an inverse calculation technique. A constitutive elastic-plastic model for strain rates in the range 10^-4-10⁴s^-1 is then proposed for sheet metals. The thermal softening due to the adiabatic conditions of the dynamic test was taken into account in creating this model.