Quasi-static and Thermoviscoelastic Response of Carbon/Epoxy–Aluminum FMLs: Effects of Stacking Sequence and Graphene–TiO2 Nano-modification

Carbon/epoxy–aluminum fiber metal laminates (FMLs) offer high specific performance and damage tolerance, yet their response is strongly governed by the stacking sequence and interfacial load transfer. In this study, we investigate the how stacking sequence and graphene–TiO2 nano-modification of the epoxy matrix influence the quasi-static and thermoviscoelastic behavior of carbon/epoxy–Al FMLs. Three architectures were considered: a CFRP reference, a two-aluminum-ply laminate, and an interface-rich alternating configuration. Neat and nano-modified epoxy matrices were compared, and selected specimens were tested in reverse orientation to investigate face placement during bending. Tensile and three-point bending tests were complemented by dynamic mechanical analysis (DMA) to track storage modulus and damping. Nano-modification increased tensile strength from 750 to 928 MPa for the CFRP reference and from 384 to 599 MPa for the interface-rich laminate, while modulus gains remained moderate. In bending, flexural strength increased by about 27 to 34% in the CFRP-rich and two-aluminum-ply laminates and by about 47 to 51% in the alternating architecture. Reverse loading further stabilized the bending response through favorable face placement. DMA showed higher storage modulus in the glassy region and an upward shift in Tg of approximately 5 to 7 ℃. Across all laminates, flexural modulus tracked DMA storage modulus, indicating that thermoviscoelastic stiffness captures architecture and interface-driven stiffness changes consistently.