Static and dynamic characterization of agglomerated cork and related sandwich structures

The aim of this experimental investigation is to assess the response to low velocity impacts of green sandwich structures made of agglomerated cork encapsulated between two thin flax/epoxy face sheets. Three different cork densities were considered to assess their role on the response to impulsive loading, both in low and high strain rate conditions by Split Hopkinson Pressure Bar (from 90 to 238 1/s). The performance of these structures has been compared to that obtained with similar specimens using a traditional synthetic foam core. Despite the lower quasi-static mechanical properties of high-density cork (modulus and collapse stress of 117.65 ± 4.04 MPa and 4.29 ± 0.06 MPa, respectively), the cork-based structures exhibited a higher perforation threshold (94.41 ± 2.37 J) than synthetic foam-based sandwiches (79.71 ± 2.24 J) for impacts at room temperature. Finally, the material performance was evaluated under different temperatures, namely −40 °C and +80 °C, where perforation thresholds were found to be higher for cork-based structures (113.98 ± 6.04 J and 101.05 ± 2.42 J) compared to synthetic foam-based sandwiches (94.39 ± 2.20 J and 77.64 ± 1.70 J). The results show that the distinctive deformation mechanisms of cork allow to tailor the response to impulsive loading with a tunable damage extension through-the-thickness, despite a pronounced temperature dependent behaviour compared to synthetic foam.