Multi-scale variability of sandwich architecture with bamboo strip reinforced composite skins: An issue for packaging stress analysis?

Abstract

This article investigates bio-based composite materials under working conditions representative of packaging logistics units (LUs) subjected to compression. A multi-instrumented technological evaluator (MITE), a large-scale testing concept, is employed to capture structural behaviour according to a given specification of work. Based on previous publications, the study focuses on bamboo strip-reinforced polymer composites, which exhibit spatial variability typical of bio-based strip reinforcements. First, the main sources of variability in bamboo are qualitatively illustrated, from the culm to the dry reinforcement fabric, specifically the patented Cobratex^® 2 × 2 twill. Second, bio-based sandwich panels are manufactured, from which MITEs, representative of packaging panels with reinforced bamboo strip skins and elementary coupons are extracted. At this stage, two processes are compared: resin infusion and compression moulding. Third, at the coupon size, reinforcement volume fraction is estimated, and elastic properties of bamboo skins are evaluated using the law of mixtures with a choice of virtual unidirectional ply stacking sequence. Some property values are updated or tuned as input data through a dialogue between finite element modelling (FEM) and experimental three-point bending tests. Finally, on MITE size, analyses are carried out, updating the chosen elastic property values of bamboo skins of the MITE, where it was subjected to a convenient kinematics thanks to multiaxial tests. This ensures a suitable accordance between FEM results and the structural response experimentally studied by means of MITE. The MITE approach demonstrates that reliable and consistent stress analysis of packaging LUs subjected to compression is possible despite the inherent multi-scale variability of bamboo-reinforced skins of sandwich panels.