8. Constitutive Modeling of the Dynamic Behavior of Cork Material

In this work, compression tests have been carried out at different strain rate, from 10⁻³ to approximately 10³ s⁻¹, on agglomerated cork material. The quasi-static and low strain rate tests have been conducted by means of servo-pneumatic machine, whereas the high strain rate tests have been conducted by means of polymeric Hopkinson bar. The experimental results show a stress–strain relationship that is characterized by a typical S-shaped curve. As expected, the strength is observed to increase when the material is deformed at increasing strain rate. In addition, the properties during the relaxation phase have been considered as well, showing that the stress response is characterized by a rapid decrement while the deformation is almost completely recovered. The global mechanical behavior is found to be very well reproduced by a combination of constitutive models, which include compressible hyperelastic modeling and large-strain viscoelasticity. The matching between the experimental and analytical data is very precise in the monotonic loading phase. Moreover, considering a damage model of the Mullins type it is possible to reproduce reasonably well also the unloading phase.