Experimental characterization of small thickness elastomeric layers submitted to impact loading

An experimental device has been developed to submit small thickness (<6 mm) elastomeric layer specimens to reproducible impact conditions at high initial impact velocities (1.9–3.8 m s−1). An impulse force test hammer is used as an impactor to measure directly the dynamic force applied on the specimen. As an alternative to classical methods in which position is measured by time integration(s) of accelerometers or velocity sensors, the measurement of the hammer position during impact is achieved by recording its motion with a high-speed camera (at a rate of 30,000 frames per second) and by detecting its position by further analysis on the individual images. Additionally, the initial impact velocity is determined from measurements of the hammer position on the images before contact. The impact model proposed only requires five parameters: two parameters for the impactor (its mass and initial impact velocity) and three parameters for the Hunt–Crossley contact force law describing the specimen. Using a relation issued from the force versus penetration depth diagrams, the estimation of these three contact force parameters can be reduced to the estimation of two independent parameters which roles are well defined and distinct; therefore this estimation can be accomplished with a straightforward trial and error procedure. The method is used to characterize eight impacted elastomeric specimens and is validated with comparisons between experimental and simulation results. These comparisons show that the model is appropriate to simulate with reasonable precision the main experimental characteristics of force and penetration depth signals.