Evaluation of Stress Equilibrium in Dynamic Tests on Agglomerated Cork

In this work, experimental compression tests have been performed on rectangular specimens cut from a cork slab. The tests have been performed both using a quasi-static testing machine and a Split Hopkinson Bar. The dynamic tests revealed a high sensitivity of the material to the strain rate, with stress strain curves significantly higher than in quasi-static condition. Given the low density of the cork, the specimen material may suffer from non-equilibrium; for this reason, a high speed camera was used to frame acquire pictures of the sample during the deformation, which have been used to perform DIC analyses. Indeed, inhomogeneous strain distributions were found, especially due to the low density of samples tested at the higher speed. Moreover, the low impedance of the tested material also determines difficulties in signal synchronization and, hence, in the correct calculation of the stress in the sample. Data from DIC analyses were then used to calculate the true strain in different portions of the specimen and to evaluate the stress due to inertia effect.