Computational and Experimental Investigation of Peel and Shear Stress Distribution in Adhesive bonded Hybrid Sisal-Glass Reinforced HDPE Composite for Automobile Side Body Panel

Abstract

This study presents an integrated computational and experimental study of peel and shear stress distributions in adhesively bonded single-side strap joints (ABSSSJ). These joints comprise a hybrid sisal-glass reinforced HDPE lower adherend and a steel upper adherend for au- tomobile side body panel applications. The study combined fabrication and mechanical (tensile and lap-shear) testing of hybrid composites with different fiber ratios and stacking sequences; parametric Cohesive Zone Model (CZM) based finite-element simulations in ANSYS; and an analytical variational-method (VM) solution for interfacial stress functions to cross-validate nu- merical predictions. Adhesive properties (modulus 1.85–6.0 GPa), adhesive thickness (0.2–1.0 mm) and cohesive fracture toughness (G_IC  = 25–1.0 kJ·m⁻²) were varied.  Environmental conditioning (moisture exposure 2–10 hr and Temperature 25–45^◦C) was included to assess durability effects. Key quantitative findings include that peak peel stress consistently occurs at the free edge of the overlap, while shear stress concentrates at the overlap ends. Increasing adhesive thickness from 0.2 to 1.0 mm reduced the peak peel stress (∼12.3 → 8.7 MPa, ≈ 29% reduction) while producing modest increases in shear strain.  The optimal joint performance occurred at an adhesive thickness ≈ 0.5 mm and G_IC  ≈ 0.75 kJ·m⁻².  The experimentally measured maximum shear strength of ABSSSJ reached 18.4 MPa (for 0.5 mm adhesive), and the tensile strength for the best stacking sequence (G–S–G) was 62.3 MPa. The CZM–FEM and VM predictions agreed closely with experimental results (deviation ≤ 8%), demonstrating the predictive capability of the combined approach. Moisture and elevated temperature degraded cohesive stiffness and increased the peel stress by 8–15%, underscoring the importance of accounting for environmental effects in design. These results advance both the mechanistic understanding and engineering readiness of recyclable, natural–synthetic hybrid composites for lightweight automotive structures.