Temperature, strain rate and anisotropy effects on compressive response of natural and synthetic cellular core materials

The remarkable flexural properties of sandwich structures hinge on the selection of performing core materials with suitable out of plane mechanical properties, i.e. compressive ones. For this reason, this work compares the compressive behaviour of a synthetic foam (polyvinyl chloride) and an environmentally friendly agglomerated cork as a function of density, strain rate, temperature and anisotropy. The strain rate sensitivity of these cellular materials was investigated in a wide range of velocity conditions by using drop weight tower and Split Hopkinson Pressure Bar dynamic compression tests. The results highlighted a remarkable strain rate sensitivity of both materials because of their viscoelastic nature and, in particular, an increase in compressive properties with increasing strain rate. This increment was more pronounced in the medium-high strain rate range than in the low-medium one. An embrittlement effect with decreasing temperature was detected, which compromises core materials crashworthiness determining a reduction of the percentage absorbed energy. Despite a remarkable anisotropy induced by the production processes, this work confirms the feasibility of agglomerated cork as a sustainable alternative to petroleum-based cellular core materials especially in consideration of the significant recovery capabilities that ensure a higher dimensional stability of the sandwich structure.