Mechanical Damage Behavior and Self-Healing Mechanism of PU-PDA/EP Composites

Epoxy resin (EP), widely used in composites, exhibits brittleness and high internal stress due to its high cross-linking density after curing, driving extensive modification studies. This work integrates polyurethane (PU) via interpenetrating networks and polydopamine (PDA) nanoparticles to fabricate PU-PDA/EP composites, investigating their mechanical and self-healing properties. Tensile/hardness tests reveal improved mechanical strength, while infrared spectroscopy and scanning electron microscopy clarify the self-healing mechanism: PDA forms hydrogen bonds with epoxy groups, enabling autonomous repair within the matrix. Digital scattering correlation method analysis tracks deformation behavior, showing stress–strain, gray coefficient (Stc), and X-direction strain (Sts) evolution under load before/after repair in diverse environments. Optimal self-healing occurs at 0.6% PDA: specimens regain 104.45% of initial strength (28.57 MPa postrepair vs. 28.16 MPa initial) after 3-day ambient healing, surpassing original performance. The study confirms PDA's dual role in enhancing toughness and triggering reversible hydrogen-bond-driven repair, offering a facile strategy to overcome EP's brittleness.