Variational Method and CZM-Based FEM Mechanical Strength Assessment of Adhesively Bonded Hybrid Sisal-Glass Reinforced HDPE Composite For Automobile Side Body Panel Application

This study investigates the mechanical strength and interfacial behavior of adhesively bonded single-side strap joints (ABSSSJ) consisting of steel and hybrid sisal-glass reinforced high-density polyethylene (HDPE) composite for automotive body panel applications.The objective of the study to investigate the mechanical strength and failure behavior of adhesively bonded steel-to-hybrid sisal-glass reinforced HDPE composite joints using a combined variational and CZM-based FEM approach. A hybrid computational framework is developed that integrates variational methods with cohesive zone modeling (CZM)-based finite element analysis (FEA) to predict stress distributions, failure initiation, and propagation across the adhesive layer. The model is validated against experimental results under varying adhesive thicknesses, overlap lengths, and fracture toughness values. Parametric studies reveal the influence of geometric and material parameters on the joint’s ultimate load-carrying capacity, peel and shear stress concentrations, and energy absorption capabilities. The results confirm that appropriate tailoring of adhesive parameters and hybrid composite layups significantly enhances bonding performance and failure resistance. The proposed approach provides a robust design methodology for hybrid fiber-reinforced polymer–metal joints in lightweight vehicle structures, ensuring both structural integrity and material sustainability.