J.F. Patrick, J.S. Turicek, Z.J. Phillips
North Carolina State University,
United States
Keywords: self-healing, damage-sensing, multifunctional, bioinspired
Summary:
Natural composites (e.g., bone, wood) have evolved sophisticated mechanisms for damage detection and self-repair, which help preserve structural function throughout their lifespan. Akin to their natural counterparts, synthetic fiber-reinforced polymer (FRP) composites inherit superior mechanical properties (high specific strength / stiffness) from a hierarchical arrangement of constituent materials. However, FRP composites do not yet mimic synergistic sensing/healing functionality. One damage mode of particular interest, interlaminar delamination, whereby fiber reinforcement debonds from the polymer matrix, has plagued FRP composites since their introduction nearly a century ago. This subsurface damage is difficult to detect and often requires costly and labor-intensive manual intervention to repair. While self-healing and damage sensing strategies have been separately developed over the years, coupling such functions for reliable and repeatable in-service performance in structural FRP composites has remained elusive. Here we present an approach for synergistic and sustained self-sensing/healing of delamination damage in FRP composites via electrical monitoring of conductive polymer fibers (cPFs), which signal and autonomously regulate thermal remending of 3D-printed thermoplastic interlayers. By synchronizing the in situ damage sensing and self-healing processes, 100 fracture/repair cycles are achieved. Self-healing efficiency, quantified by the ratio of mode-I critical strain energy release rate (i.e., GIC), sustains 80% of the virgin fracture resistance for all cycles. Remarkably the electrical conductance of the cPF slowly increases with increased cycling demonstrating sensor improvement rather than deterioration. Thus, this newfound self-sensing and self-healing strategy creates competitive advantage for FRP composites, particularly those in erratic and inaccessible environments (e.g., space) where remote structural interrogation and autonomous self-repair is mission critical.