An experimental study on the effect of fatigue loading on electrical impedance in open-hole carbon nanofiber-modified glass fiber/epoxy composites

Fiber-reinforced composites (FRCs) are valued for their high specific properties. However, FRCs are vulnerable to difficult-to-predict damage growth and complex failure modes thereby motivating the need for robust structural health monitoring (SHM). Self-sensing via nanofiller-induced piezoresistivity has much potential for this. Research in piezoresistivity to date has overwhelmingly focused on the direct current (DC) response. This is important because alternating current (AC) has important benefits such as improved data density, potential for greater sensitivity, and reduced power requirements. In light of the potential of AC-based methods, this work explores AC transport responsiveness to high-cycle fatigue loading in carbon nanofiber (CNF)-modified glass fiber/epoxy laminates via equivalent circuit analyses. These results show that equivalent circuit behavior is significantly affected by fatigue-induced damage accumulation suggesting a mechanism for monitoring fatigue. However, clear circuit parameter evolution-load cycle trends were not observed suggesting further work is needed to fully realize the potential of AC-based monitoring.