Functionally Graded Hybrid Composite Engineering Using GFRP, Bamboo, and Banana Fibres for Sustainable Structural Systems

A functionally graded hybrid composite (FGHC) was developed using bamboo and banana natural fibres within a Glass Fibre Reinforced Polymer (GFRP) framework to address limitations inherent in conventional hybrid composite design. The laminate was fabricated via hand lay-up followed by compression moulding, with a symmetric six-layer stacking sequence [Banana/Glass/Bamboo/Bamboo/Glass/Banana]. Natural fibres were subjected to 5 wt% NaOH alkaline treatment to improve fibre–matrix interfacial bonding. Tensile testing (ASTM D638-14) yielded a mean strength of 107.0 ± 1.9 MPa with a Young's modulus of 5.65 ± 0.04 GPa. Flexural evaluation (ASTM D790-17) recorded a peak load of 1.616 ± 0.012 kN and a flexural strength of 79.3 ± 0.6 MPa. Izod impact testing (ASTM D256-10) produced a mean impact strength of 12.0 ± 0.2 kJ m−2. All specimens exhibited progressive failure rather than catastrophic fracture, indicating effective energy dissipation. The graded architecture, in which GFRP bears primary loads, bamboo deflects cracks, and banana fibres absorb peripheral energy, yields mechanical performance superior to binary natural fibre systems. This study establishes a mechanistically justified design strategy for sustainable lightweight structural composites applicable to automotive, panel, and civil construction sectors.