Enhancing the performance of honeycomb core sandwich panels through friction stir spot welding strategies and fracture of lap shear specimen

Abstract

The manufacturing of honeycomb core sandwich structures using friction stir spot welding (FSSW) methods as alternatives for adhesive bonded (AB) structures is examined. AB, FSSW with disk insert (FSSW_D), FSSW_D with AB (FSSW_D_AB) are adopted for the purpose. The performance during the lap shear test and the cohesive zone modeling (CZM) in the finite element (FE) simulation served as the foundation for the comparison. A homogenized core and equivalent cohesive layer were used during the numerical simulations of lap-shearing of all joints. Maximum load-carrying capacity improved significantly when the FSSW_D and FSSW_D_AB were used; the improvement ranged from 592% to 878% over AB joints. Peak load was shown to be around 24% higher in FSSW_D_AB in comparison to FSSW_D joints. The peak load-to-weight ratio of the FSSW_D_AB joints was remarkable (542% to 747%). Stiffness measurements were approximately 0.43 kN/mm for FSSW_D and 0.63 kN/mm for FSSW_D_AB joints. Microstructural analysis revealed finer grains with increased rotation speed and distinct fracture modes, with SEM showing improved ductility. The good agreement between the numerical predictions and the experimental results for all types of joints showed the usefulness of the proposed numerical model. Moreover, FE simulations-based stress analyses of the three joints provided crucial results on normal and shear stress distributions enabling the sandwich structures to be tailor-made for their intended applications.