Enhanced cellulose paper interfaces with MWCNT/Graphene for improved structural health monitoring and mechanical performance in CARALL

Carbon fiber reinforced aluminum laminates (CARALL) suffer from weak metal–composite interfaces and the lack of built-in damage sensing. Here, cellulose paper interleaves loaded with hybrid multi-walled carbon nanotubes (CNTs) and graphene (5–9 wt% at 160 or 210 g/m2) are fabricated by conventional papermaking and inserted at the Al/CFRP interface. CARALL panels were produced via hand lay-up and vacuum bagging and evaluated under tensile, three-point flexural, and Mode-I fracture tests, with damage events monitored in situ through piezoresistive electrical resistance measurements (?R/R). The 210 g/m2 paper with 9 wt% hybrid nanofiller maintains baseline tensile strength and yields up to ? 20 % higher flexural strength versus unreinforced CARALL, while interlaminar fracture toughness increases during both initiation and propagation. Microscopic observations reveal fiber bridging/pull-out and crack deflection within the paper interlayer, while the formation of a percolated CNT/graphene network enables clear piezoresistive responses. Abrupt ?R/R jumps were observed at final failure under tensile loading (approximately twofold), whereas event-correlated ?R/R fluctuations were recorded during flexural and Mode-I fracture tests (typically in the range of ? 0.25–2 during flexure and ? 0.5 to + 0.5 during double cantilever beam tests). The results demonstrate that lightweight, low-cost cellulose-nanocarbon interleaves simultaneously toughen CARALL and provide integrated structural health monitoring capability. © 2026 Elsevier Ltd.