Influence of Stacking Sequence on the Ballistic Response of Raffia/Carbon Fiber-Reinforced Epoxy Hybrid Composites Subjected to 9 mm Projectile Impact

Hybrid composites combining natural and synthetic fibers have emerged as promising materials for lightweight ballistic protection systems due to their ability to balance mechanical performance, energy absorption, and sustainability. This study investigates the influence of stacking sequence on the ballistic response of epoxy hybrid composites reinforced with raffia and carbon woven fabrics subjected to 9 mm projectile impact. Four stacking-sequence configurations were investigated: alternating laminates (R2C2)3 and (C2R2)3, and block laminates R6C6 and C6R6, all containing identical reinforcement contents. Ballistic response was evaluated through impact and residual velocities, velocity reduction, absorbed energy, energy absorption efficiency, momentum reduction, and Doppler radar velocity profiles. All laminates were completely perforated but maintained their structural integrity after impact, without catastrophic fragmentation. The results showed that architectures with carbon fiber layers positioned at the impact face, namely (C2R2)3 and C6R6, exhibited the lowest residual velocities and the highest absorbed energies, reaching 136.8 J and 135.4 J, respectively. Energy absorption efficiencies ranged from 16.6% to 19.1%, indicating similar ballistic responses among all configurations. Statistical analysis revealed no significant differences among the investigated architectures (p > 0.05). Overall, the results indicate that the impact-face reinforcement exerts a secondary influence on ballistic response, whereas the total reinforcement content governs energy dissipation during projectile penetration.