Low energy impact evaluation using non conservative models

The aim of the present work is the evaluation of mechanical properties of polymer and polymer matrix composites by using a low energy impact technique on a flexure plate configuration, which consists of a plate that is hit by a semispherical indenter. For the analysis of the force-time histories acquired experimentally a non elastic and non conservative model that includes the permanent deformations due the flexion and indentation produced by the impact is proposed. The model proposed has two systems set up in a serial arrangement. The first one is a spring-dashpot and the second is a hertzian spring-dashpot that simulates the indentation. Since the differential equation that describes this system does not have an analytical solution a 4th order Runge–Kutta algorithm was used. The overall energy loss was calculated by means of the restitution coefficient that was measured experimentally; these results were compared with those obtained solving the differential equation. Eight sets of samples of polystyrene (PS) matrix composite with elastomeric and rigid dispersed phases were tested. A good correlation between the analytical and experimental results was observed, which allowed the calculation of the elastic modulus at high loading rates and the determination of the energy necessary to initiate damage of the specimen.