Mechanical performance and failure analysis of functionally graded Nanoclay-GFRP composites under flexural and shear loading

This study provides a novel gradation-based design for tailoring flexural and shear performances, offering a thorough experimental and statistical examination of the mechanical behavior of functionally graded nanoclay-reinforced glass fiber composites. Instead of traditional uniform composites, the proposed laminates adopt stepwise and continuous nanoclay gradation through the thickness to improve stress distribution and interfacial bonding. Five different laminates were produced utilizing a hand lay-up method accompanied by vacuum-bagging. The fabricated laminates include Control (neat composite), Homogeneous-Graded (HG), Stepwise-Graded (SG and CG), and Functionally-Graded (FG). The mechanical examination included three-point flexural, interlaminar shear (ILS), and in-plane shear testing. The results indicated that nanoclay addition improved interfacial interaction, limited crack growth, and facilitated entire load transfer. The FG laminate had the maximum flexural strength and stiffness, whereas the CG laminate produced 20.7% increased toughness and failure strain. The SG laminate produced the highest in-plane shear and load, achieving 71.56% and 93.8%, respectively. Fractographic analysis revealed a transition from brittle, delamination-dominated fracture in the control to tough, gradual modes in graded laminates. A multi-objective (TOPSIS) determined that the SG laminate was the best design for global performance. This study indicates functional gradation's practical value in producing multipurpose effective, robust composite structures for modern structural and engineering applications.