Quasi-static and fatigue properties of a balsa cored sandwich structure with thermoplastic skins reinforced by flax fibres

This paper presents the results of several experimental analyses performed on a bio-based sandwich structure. The material studied is made up of thermoplastic skins reinforced by flax fibres and applied to a balsa core. It is produced by a single-step liquid resin infusion process. First, the skin-core interfacial properties were measured and compared with those of the existing materials. Then, several quasi-static and dynamic analyses were performed to study the flexural behaviour of sandwich beams. The elastic and ultimate properties of the skins and core were deduced from these flexural tests. In addition, a failure mode map was developed based on the existing theories to explain the failure modes observed under different boundary conditions. The influence of the statistical spread of the core's mechanical properties on the failure of sandwich beams was considered. Moreover, fatigue analyses were conducted to determine the fatigue resistance of this bio-based structure. Its behaviour was compared with that of the previously tested non-bio-based sandwich beams. Finally, the fatigue loss factor evolution of this structure under several loading ratios was measured and discussed. This study aims to determine some of the main mechanical properties of this material to see whether or not it might be suitable for industrial applications currently using glass fibre reinforced polymer/foam cored sandwich structures.