Post-impact residual strength and resilience of sandwich panels with natural fiber composite faces

In this paper, the post-impact residual flexural behavior of sandwich panels with flax fiber-reinforced polymer (FFRP) faces and polyisocyanurate (PIR) foam cores is investigated experimentally. The faces were manufactured using a wet lay-up procedure with a balanced bidirectional 2x2 twill flax fiber fabric and a bio-based epoxy with a bio-content of 30%. Each specimen was 1200 mm long x 75 mm wide x 80 mm thick. The main parameters in the study were the face thickness (one, two or three FFRP layers, representing core-to-skin thickness ratios of approximately 54, 28 and 20) and core density (32, 64 or 96 kg/m(3)); a total of nine combinations. In this study, 27 specimens (three specimens for each combination) were tested under impact loads and the surviving specimens were tested under monotonic three-point bending. Each of the three identical specimens was tested under different impact condition, namely 100%, 75% and 50% of the energy resistance of an intact specimen, with the last two impacted 50 times. The results of the post-impact residual flexural tests were compared to three-point bending tests of intact specimens. The beams demonstrated remarkable resilience in that the impact events did not have a negative effect on their flexural strength or stiffness. In fact, those tested at higher energy levels exhibited a slight increase in strength after impacts. This shows their suitability for use in infrastructure applications such as building cladding panels, flooring and roofing as they retain their strength and stiffness even after multiple impacts.