The split Hopkinson pressure bar technique is extensively used to characterise material behaviour at high strain rates. In this paper, this technique is re-examined in order to optimise its accuracy, to improve its capacity and to develop innovating applications.
The accuracy of the basic SHPB measurements which are forces and velocities at both sample faces is discussed and it depends on data processing which consists mostly of an accurate dispersion correction and of an exact delay setting. A deconvolution method is developed to increase measuring duration and consequently the maximum measurable strain.
A one-dimensional numerical transient simulation of SHPB tests is used to analyse the validity of the average stressstrain curve obtained from measured forces and velocities. A fictitious specimen with a rate-sensitive behaviour described by a Sokolovsky-Malvern type constitutive model is used for this simulation. For the case where the classical SHPB analyses do not give acceptable results, an identification technique based on an inverse calculation method is presented. It permits relating material properties to forces and particle velocities measured at both faces of the specimen without using the assumption of axial uniformity of stresses and strains.
Structural tests using a large SHPB, crushing of metallic tube for instance, can be performed in order to provide accurate data to validate identified constitutive laws. Simulations with commercial explicit code (Radioss) showing a good agreement with experimental data is also presented.