Determination of stress-time histories in axially symmetric impacts with the two-gauge technique

We present an experimental technique for the direct measurement of stress-time histories in axially symmetric dynamic impacts, where the state of strain is not uniaxial. The technique is based on placing two different well-calibrated piezoresistance gauges in the desired location on the symmetry axis. The two measured resistance changes are then substituted in a system of two equations with two unknowns from which one obtains the axial stress and the lateral strain histories. We demonstrate the technique with manganin and constantan gauges which were calibrated both under uniaxial strain and hydrostatic conditions. As an example we bring the results of stress measurements inside thick polymethyl methacrylate targets which were impacted by thick copper discs. The measured stress-time history is then compared to that predicted by a two-dimensional Lagrangian code.