Ultra-tough architected adhesive joints for integrated composite processing and bonding

Deployment of advanced polymer-based composites in critical structures requires, among others, breakthroughs in adhesive bonding solutions. Indeed, available methods still suffer from limited fracture toughness of adhesives and from time-consuming bonding processes. Here, we demonstrate a novel concept of architected thermoplastic joints with exceptional fracture resistance up to 5000 J/m, fully integrated with the composite resin transfer molding process, hence simultaneously targeting both limitations. This extreme toughness is activated through controlled 3D printed hollow pattern within a Nylon bondline. A synergetic combination of plastic dissipation, crack deflection, branching and arrest is tuned by changing the pattern characteristics. Three failure regimes are unraveled through fractographic analyses and finite element models. A stress-at-a-distance fracture criterion, identified for each constituent, quantitatively predicts the toughness variations along the crack path. This approach, amenable to dissimilar bonding between metals and composites, paves the road towards novel and higher performance structures and manufacturing approaches.