Dynamics of supersonic microparticle impact on elastomers revealed by real–time multi–frame imaging

Understanding high–velocity microparticle impact is essential for many fields, from space exploration to medicine and biology. Investigations of microscale impact have hitherto been limited to post–mortem analysis of impacted specimens, which does not provide direct information on the impact dynamics. Here we report real–time multi–frame imaging studies of the impact of 7 μm diameter glass spheres traveling at 700–900 m/s on elastomer polymers. With a poly(urethane urea) (PUU) sample, we observe a hyperelastic impact phenomenon not seen on the macroscale: a microsphere undergoes a full conformal penetration into the specimen followed by a rebound which leaves the specimen unscathed. The results challenge the established interpretation of the behaviour of elastomers under high–velocity impact.United States. Office of Naval Research (ONR DURIP Grant No. N00014-13-1-0676)United States. Army Research Office (Grant W911NF-13-D-0001

Application of the Virtual Fields Method to Rubbers Under Medium Strain Rate Deformation Using Both Acceleration and Traction Force Data

This paper describes an experimental technique for characterizing the uniaxial stress-strain relationship of rubbers under medium strain rate deformation. This method combines the Virtual Fields Method (VFM) and high-speed imaging with digital image correlation. The VFM can be expressed so that force measurement during dynamic loading is no longer required; instead, surface measurements of acceleration, which occurs as a result of wave propagation in the specimen, are used as a ‘virtual load cell’. In a previous paper, the authors have utilized this technique for characterizing material parameters for the dynamic behaviour of rubbers using a drop-weight apparatus. One limitation of this technique is that the stability of the parameter estimation depends on the length of the specimen. When the loading stress wave reaches the fixed end of the specimen, a static equilibrium state is instantaneously achieved. At this instant, the acceleration fields are no longer able to provide information, and the identification is unstable. In order to overcome this limitation, the present paper proposes a VFM based method able to produce stable identification even at this equilibrium instant. This procedure utilizes both inertial and external forces, and a new experiment apparatus has been developed for simultaneously measuring these two sets of data. This new procedure is described using results from simulations; then, the experimental system and results will be presented