Session: 03-12-01: Structural Bonding and Surface Modifications

Paper Number: 190413

190413 - Engineered Interleaves for Robust and Repairable Co-Cured Cfrp Joints: Nanofiber Toughening and Reweldable Vitrimer Films 

Lightweight structures rely on bonded composite joints, yet two persistent limitations restrict reliability and lifecycle sustainability: (i) interface variability driven by reinforcing textile architectures (e.g., yarn crimp and effective 0°|90° mismatch at the bondline) and (ii) the irreversibility of thermoset bondlines. This presentation introduces an “engineered interleaf” strategy that addresses both challenges using multiscale interleaving methods compatible with co-curing of woven carbon/epoxy prepregs.  

First, we demonstrate that electrospun nanofibrous veils placed at the bondline can mitigate mismatch-driven strength loss in co-cured single-lap joints manufactured from 8-harness satin (8HS) laminates. When the dominant yarn orientations at the interface are mismatched (0|90), lap-shear failure load is 25–27% lower than matched (0|0) and (90|90) configurations. Nanofiber interleaving restores this loss, bringing the (0|90) joint back to strength levels comparable to the matched cases. Across configurations, nanofibers increase failure load by ~12% for (0|0) and ~25% for (0|90). Two-way ANOVA and analysis of means confirm that both interface orientation and nanofiber interleaving significantly influence joint strength, with a strong interaction effect (p < 0.001). Fractography indicates that nanofibers enhance delamination resistance by stabilizing crack paths and suppressing crack jumps at crimping and yarn-intersection sites.

Second, we extend the interleaf concept from “toughening” to “programmable bonding” by integrating a commercial epoxy vitrimer (Vitrimax™ T100) as a supported film adhesive reinforced with a nickel-coated carbon-fiber (Ni-CF) nonwoven during co-curing. Relative to epoxy-only references (~12 MPa), vitrimer-film joints achieve higher pristine single-strap lap-shear strength and reach ≈23 MPa after a brief post-heat activation step (180 °C, 1 MPa, 5 min). Most importantly, an optimized processing route enables re-welding from as-fractured surfaces without adding new adhesive or performing surface preparation, recovering ≈75% of post-heated pristine strength after the first re-weld and ≈55% after three re-weld cycles. Differential scanning calorimetry shows a nearly invariant Tg (~50–56 °C) with thermal history, while enthalpy-relaxation trends correlate with re-weld retention, motivating a practical “activation window” that links film pre-state and thermal schedule to strength and re-weldability.

Together, these results position multiscale interleaves—nanofiber veils for mismatch tolerance and vitrimer/Ni-CF films for re-activatable interfaces—as scalable routes to robust, repairable, and potentially multifunctional composite assemblies (with a clear pathway to localized Joule heating and resistance-based self-sensing at the bondline).

Presenting Author: Melih Papila California State University Northridge

Presenting Author Biography: Dr. Melih Papila is an Assistant Professor in the Mechanical Engineering Department at California State University, Northridge. He earned his Ph.D. in Aerospace Engineering from the University of Florida and previously served on the faculty of Sabancı University, with visiting researcher appointments at Stanford University. His research advances sustainable, multi-scale, multifunctional composites and structures, with emphasis on experimental mechanics and simulation-coupled predictive modeling. Current efforts include vitrimer-based, reworkable adhesive films and co-cured composite joints enabled by embedded Joule heating and electrical self-sensing for field-ready repair and reuse.