Experimental mechanical performance and optimized micromechanical modeling of almond and pistachio bio-waste-reinforcement glass-epoxy composites

Abstract

The increasing need for sustainable and economical composite materials is driving interest in replacing traditional synthetic fillers with eco-friendly, bio-based reinforcements. The cumulative effects of agricultural waste microparticles, particle size, post-curing processes, manufacturing imperfections, and tensile testing conditions on the mechanical properties and predictive modeling of glass–epoxy composites are not yet well understood. This work experimentally examines the tensile properties and dependability of glass–epoxy composites reinforced with microparticles derived from almond and pistachio bio-waste. Composite laminates are produced via the vacuum infusion process (VIP), with or without post-curing, and are evaluated through tensile testing. The impacts of reinforcement type, microparticle size, curing conditions, void formation, tab material, and adhesive type are assessed. The experimental data are subsequently compared with the Voigt–Kran, Reuss–Kran, Voigt–Reuss–Hill, Bowyer–Bader, Cox, and Cox–Krenchel micromechanical models to determine which model most accurately predicts the observed behavior. The findings indicate that the inclusion of 1 wt% almond and pistachio microparticles enhances Young's modulus, ultimate tensile strength, and fracture energy by up to 14.5%, 23.4%, and 22.52%, respectively. Smaller microparticles enhance the efficiency of reinforcement by facilitating more effective stress transfer between the reinforcement and the matrix. Post-curing enhances the mechanical properties of the laminates, augmenting Young's modulus, ultimate tensile strength, and fracture energy by up to 9.8%, 18%, and 15.5%, respectively. In contrast, void defects diminish fracture energy by roughly 39.2%. Composite tabs yield more reliable tensile measurements than aluminum tabs; however, epoxy adhesive enhances bonding effectiveness by facilitating cohesive failure within the composite. Of the assessed analytical models, the modified Voigt–Reuss–Hill model demonstrates the most accurate correlation with the experimental findings. The findings indicate that microparticles derived from recycled almond and pistachio bio-waste serve as an effective and sustainable reinforcement method for high-performance glass-epoxy composites in lightweight engineering applications. The findings indicated that the presence of bubbles and aluminum tab resulted in a decrease of 4.82 and 9.3 % in Young's modulus, respectively. Almond shell at 38 μm, almond shell at 120 μm, and pistachio shell at 120 μm increased Young's modulus by 14.66%, 3.7%, and 9.68%, respectively.