Energy Absorption of Natural-Fiber-Reinforced Composites: Influencing Factors, Mechanisms, and Sustainability Perspectives

Natural-fiber-reinforced composites (NFRCs) have been shown to be an alternative material for use in impact protection and crashworthiness because of their low density, favorable specific properties, renewable resources, and potential environmental benefits. This paper will cover the mechanisms and key parameters governing the energy-absorption behavior of natural-fiber-reinforced composites, with emphasis on fiber and matrix types, fiber–matrix interfaces, particulate modification, reinforcement architecture, fiber orientation, stacking sequence, fiber volume fraction, environmental conditions, and structural geometry. The available evidence shows that energy is dissipated through matrix cracking and plastic deformation, interfacial debonding and sliding, fiber bridging, pull-out and fracture, crack deflection, delamination, and progressive crushing. Maximizing fiber strength, interfacial adhesion, fiber content, or laminate thickness does not necessarily maximize energy absorption. Instead, optimal performance requires a balance between effective load transfer and stable progressive damage. Moisture can further produce competing effects through short-term plasticization and long-term interfacial degradation. Current research is limited by inconsistent testing protocols, insufficient normalization of energy absorption metrics, incomplete understanding of multiscale damage evolution, and limited long-term and component-scale validation. Future studies should integrate multiscale characterization, validated numerical modeling, standardized testing, and multi-objective optimization to develop lightweight, damage-tolerant, and sustainable energy-absorbing structures.