Experimental and finite element analysis of the impact response of agglomerated cork and its intraply hybrid flax/basalt sandwich structures

Sandwich structures are widespread in all the industrial applications where a high stiffness-to-weight ratio is required. Despite the unique bending performance, they feature two major drawbacks: the massive exploitation of synthetic materials and a strong susceptibility to impact damage. This work addresses both problems, investigating the puncture impact response of bio-based sandwich structures with an agglomerated cork core and intraply flax/basalt hybrid skins. A preliminary campaign of impacts was performed on three agglomerated corks with different densities and on three traditional polyvinyl(chloride) foams with comparable densities. Based upon the results obtained, one agglomerated cork (NL25) and one PVC foam (HP130) were selected to realize a finite element analysis (FEA) on the sole core and to produce the whole sandwich composites. FEA results show a good agreement with experimental ones ensuring a reliable prediction of cores dynamic response. The tests performed on sandwich structures proved the feasibility of agglomerated cork as an effective core, able to provide an improved damage tolerance to the structure. NL25 sandwiches impacted at 20-30 J showed a permanent indentation 60-67% lower than HP130 ones. The coupling agent in skins has a detrimental effect reducing composites perforation threshold from 80 to 60 J.