Low-Velocity Impact Response and Damage Mechanisms of Hybrid Skin-Grid Natural Fiber Composite Structures: Effect of Impact Position

Abstract

This paper presents a novel all-natural “skin-grid” hybrid architecture, utilizing flax fabric skins and a sisal orthogonal grid to significantly enhance the impact resistance of green composites. A combined experimental and numerical approach (Low-Velocity Impact, Quasi-Static Indentation, Micro-CT, and Macro-Scale FEA) was employed to elucidate the synergistic load-bearing mechanisms under a critical threshold energy of 25 J. The results demonstrate that, compared to a pure flax composite baseline, the integration of the grid architecture increased the peak impact load at the Intersection by 255.34% and absorbed an additional 16.94 J of energy. Among different impact locations, the Intersection position exhibited optimal performance, achieving a peak load 35.82% higher than the unsupported Center position. Mechanistically, while the Center suffered catastrophic perforation, the Intersection and Rib positions maintained structural integrity through a progressive “tension–debonding–relaxation” damage cycle (secondary hardening phenomenon) driven by the grid’s crack arrest and synergistic load redistribution effects. The FEA model accurately predicted the global dynamic responses and damage sequences. This study validates the skin-grid concept as a highly tailorable, eco-friendly alternative for lightweight, impact-resistant applications, offering substantial practical implications for the green transition in engineering materials.