Self-Healing Efficiency of a Multidirectional CFRP Laminate After Low-Velocity Impact

The widespread use of carbon fiber-reinforced polymers (CFRPs) in unmanned aerial vehicle (UAV) structures increases the importance of understanding low-velocity impact damage, which is often barely visible yet can significantly reduce residual strength and lead to structural failure during service. This study investigates the impact behavior and healing capability of a multidirectional CFRP laminate with a thermally activated self-healing matrix (CompPair HealTech®). Laminates with a thickness of 1.45 mm were subjected to drop-weight impacts at 5 J and 10 J. After impact, specimens were thermally activated at 150 °C for 30 min and re-impacted under identical conditions. Impact response was evaluated from force, energy, and displacement histories, while residual properties were assessed by compression after impact (CAI) testing and X-ray phase-contrast imaging (XPCI). At 5 J, the re-impact response was nearly identical to the initial impact, with a peak force of approximately 2.1 kN, indicating largely reversible damage. At 10 J, the peak force decreased from ~3.0 kN to ~2.6 kN and displacement increased, reflecting incomplete stiffness recovery caused by more severe damage. Nevertheless, residual compressive strength recovered to ~99% and ~91% of the virgin level for the 5 J and 10 J conditions, respectively. The corresponding healing efficiencies were 86% and 49%. X-ray observations revealed a transition from localized matrix cracking and interfacial damage at 5 J to more extensive internal damage at 10 J. The combined analysis of impact response, residual strength, and damage morphology establishes a direct relationship between damage severity and healing efficiency, demonstrating the potential of thermally activated self-healing composites for rapid recovery of lightweight aerospace structures and UAV components.