Shear-Dominated Bending Response of CFRP/Al Sandwich Joints: Influence of Stacking Sequence, Hybrid Bonding and PAN Nanofiber Interleaves

Fiber–metal laminates (FMLs) that pair aluminum with CFRP offer an appealing balance of low weight and damage tolerance, yet their structural efficiency often depends on how well the composite–metal joints are designed. Here, we examine the shear-dominated flexural response of Al/CFRP sandwich joints and quantify how (i) stacking sequence and (ii) PAN nanofiber-interleaved toughening influence strength, energy absorption, and failure mode. Two laminate architectures were studied: Al–CFRP–Al (A–C–A) and CFRP–Al–CFRP (C–A–C). For each architecture, five joint concepts were produced using a structural epoxy: bolt-only (reference), neat bonded, PAN nanofiber-interleaved bonded, neat bonded/bolted hybrid, and nanofiber-bonded/bolted hybrid. Short-span three-point bending was selected to emphasize interlaminar and bondline shear, and load–displacement curves were used to extract maximum load, apparent interlaminar shear strength, total failure energy, and energy to maximum load, supported by post-failure observations.Nanofiber interleaves did not push bonded joints beyond the bolt-only peak-load level, but they markedly increased energy absorption and shifted failure from mainly adhesive debonding to mixed adhesive/cohesive fracture. Hybrid joints consistently outperformed both bonded and bolted configurations; with PAN toughening, nano-hybrid joints showed the highest loads and the most progressive, non-catastrophic response. Switching from A–C–A to C–A–C further enhanced strength and energy, especially for hybrids. The best-performing nanofiber-interleaved hybrid reached 6789 N (A–C–A) and 8406 N (C–A–C), about 52% and 90% above bolt-only, respectively, highlighting a robust route to simultaneous gains in strength, energy absorption, and damage tolerance.