Optimizing mechanical and ballistic properties in hybrid sisal/aramid fabrics reinforced epoxy composites through stacking sequence design

Hybrid composites combining natural and synthetic fibers or fabrics are promising alternatives for improving mechanical performance while reducing both costs and environmental impact. However, the influence of stacking sequence on the ballistic and mechanical behavior of these materials remains unclear. This study investigates how different configurations of aramid (A) and sisal (S) fabric layers influence the flexural and ballistic performance of epoxy matrix hybrid composites. In three-point bending tests, the block-stacked 6S/6A hybrid composite exhibited competitive flexural strength (116 MPa) compared to the 12A composite (143 MPa), which is reinforced solely with aramid. The interleaved stacking sequence [1A/1S] 6 also stood out in terms of elastic modulus (4 GPa) and flexural toughness (7×10 6 J/m 3 ). For 7.62 mm caliber bullets, statistical analysis (ANOVA) revealed that the different stacking sequences proposed had no significant effect on energy absorption. Ballistics tests with 9 mm ammunition showed that the 6S/6A composite performed best, absorbing 244 J/cm while reducing costs by 23% and synthetic fiber usage by 50% compared to the fully aramid-reinforced 12A composite. Fractographic analysis identified various fracture mechanisms, such as partial and complete delamination at the aramid interfaces, suggesting weak adhesion. Therefore, the results indicate that hybrid 6S/6A composites provide a cost-effective solution with improved mechanical performance and reduced use of synthetic material, making them attractive for structural and ballistic armor applications.