Multi-objective optimisation of aluminium skins and recycled/perforated PET foams sandwich panels subjected to impact loads

This work describes a methodology for the multi-objective optimisation of sandwich structures made of aluminium skins and recycled PET foams with perforated architecture. The designs are evaluated using a nonlinear finite element (FE) model validated by comparing the load, displacement and final shape of a representative sandwich panel against related experimental results. An extensive number of experiments characterise the mechanical performance of sandwich panels in pristine and perforated architected foams, the latter with perforations distributed following cubic and hexagon packing. A single lap joint test assesses the bonding between the aluminium skins and the epoxy adhesive system. Three-point bending and drop tower impact tests are performed to characterise the foams and the panels. Aluminium sheets are also tested for comparison purposes. Analysis of variance and Tukey test are used to compare the results from a statistical standpoint. The validity of the optimisation process is demonstrated through the design of sandwich panels made of hexagonal architectures of foam perforations and subjected to impact load. The sandwich panel is optimised to minimise mass and maximise the absorbed energy by using a custom routine integrated with a genetic algorithm. The results demonstrate that sandwich panels in pristine conditions provide enhanced bending performance, while panels with perforated foams have larger impact resistance. The optimisation indicates that the proposed methodology can support the design of lightweight perforated sandwich panels with superior structural performance.