Fracture and post-repair mechanical behaviors of natural fiber reinforced PLA composite sandwich structures

The use and application of natural fibers and their composites have garnered increasing attention due to their sustainability and environmental friendliness. This study investigates the after-impact and after-repair compressive and flexural behaviors of flax and cotton fiber reinforced polylactic acid (PLA) laminates (FFRP and CoFRP), along with their sandwich structures incorporating balsa wood cores. For comparison, glass fiber reinforced PLA (GFRP) and its sandwich structures were also evaluated. All composites used thermoplastic PLA as the matrix and were repaired through a heat-press method. Most FRP laminates and their sandwich counterparts exhibited good repair effectiveness, with compressive and flexural strengths largely restored to over 80% after repair. While GFRP and its sandwich structures maintained the highest overall performance, FFRP and CoFRP demonstrated comparable after-impact and after-repair behaviors. Notably, CoFRP exhibits lower modulus and strength but higher fracture energy than FFRP (1.18 kJ/m 2 vs 0.49 kJ/m 2 ), contributing to its improved toughness. Given their reasonable repairability and sustainable material base, natural fiber-reinforced PLA composites are considered viable for secondary structural applications where moderate impact resistance and environmental considerations are primary concerns.