Crack monitoring of short carbon fiber reinforced polymer-matrix composites based on the double-layer capacitance effect

Structural health monitoring (SHM) based on electrical resistance is a promising technology for ensuring the integrity of engineering structures. While electrical resistance measurement is effective for monitoring damage, extracting information related to the target damage from resistance signals typically requires additional signal decoupling techniques. To circumvent this limitation, this article proposes a crack monitoring method that provides a distinct damage signature based on the electrical double-layer capacitance effect. The core concept is that the ingress of an electrolyte into a crack alters the monitoring circuit from a purely ohmic to a capacitive system. This transformation generates a unique charge–discharge signature monitorable using a polarity-reversing voltage. The method was validated through theoretical modeling and experiments on short carbon fiber-reinforced polymer-matrix composites. Results confirm that this charge–discharge signature serves as a reliable qualitative indicator of crack presence. Furthermore, the method demonstrates excellent robustness across a wide range of applied voltages (0.5–5 V) and electrolyte concentrations (0–25/100 g water NaCl solution), showing high tolerance to crack orientation and location on nonplanar structures. By shifting the focus from interpreting quantitative resistance variations to recognizing a physically grounded capacitive signature, this study provides a novel perspective for crack monitoring, enabling more definitive damage identification in complex environments.