Smart sensing skin for detection and localization of fatigue cracks

Abstract

Fatigue cracks on steel components may have strong consequences on the structure's serviceability and strength. Their detection and localization is a difficult task. Existing technologies enabling structural health monitoring have a complex link signal-to-damage or have economic barriers impeding large-scale deployment. A solution is to develop sensing methods that are inexpensive, scalable, with signals that can directly relate to damage. The authors have recently proposed a smart sensing skin for structural health monitoring applications to mesosystems. The sensor is a thin film soft elastomeric capacitor (SEC) that transduces strain into a measurable change in capacitance. Arranged in a network configuration, the SEC would have the capacity to detect and localize damage by detecting local deformation over a global surface, analogous to biological skin. In this paper, the performance of the SEC at detecting and localizing fatigue cracks in steel structures is investigated. Fatigue cracks are induced in steel specimens equipped with SECs, and data measured continuously. Test results show that the fatigue crack can be detected at an early stage. The smallest detectable crack length and width are 27.2 and 0.254 mm, respectively, and the average detectable crack length and width are 29.8 and 0.432 mm, respectively. Results also show that, when used in a network configuration, only the sensor located over the formed fatigue crack detect the damage, thus validating the capacity of the SEC at damage localization. Fatigue cracks on steel components may have strong consequences on the structure's serviceability and strength. Their detection and localization is a dicult task. Existing technologies enabling structural health monitoring have a complex link signalto-damage or have economic barriers impeding large-scale deployment. A solution is to develop sensing methods that are inexpensive, scalable, with signals that can directly relate to damage. The authors have recently proposed a smart sensing skin for structural health monitoring applications to mesosystems. The sensor is a thin lm soft elastomeric capacitor (SEC) that transduces strain into a measurable change in capacitance. Arranged in a network conguration, the SEC would have the capacity to detect and localize damage by detecting local deformation over a global surface, analogous to biological skin. In this paper, the performance of the SEC at detecting and localizing fatigue cracks in steel structures is investigated. Fatigue cracks are induced in steel specimens equipped with SECs, and data measured continuously. Test results show that the fatigue crack can be detected at an early stage. The smallest detectable crack length and width are 27.2 mm and 0.254 mm, respectively, and the average detectable crack length and width are 29.8 mm and 0.432 mm, respectively. Results also show that, when used in a network conguration, only the sensor located over the formed fatigue crack detect the damage, thus validating the capacity of the SEC at damage localizat...

Numerical simulation and experimental validation of a large-area capacitive strain sensor for fatigue crack monitoring

“…Crack simulation through the element deletion method: (a) damage evolution model; and (b) simulation of crack growth by deleting elements where each numbered square is an element [18] and Eq. (3) [20] describe the relationships between capacitance change and strain change for uniaxial and biaxial strain fields, respectively, where C0 is the initial capacitance, εx and εy are the two principle strains, ν is the Poisson's ratio of the sensing material with a typical value of 0.49. However, both equations are still difficult to be implemented in the FE analysis, because the strain result in FE analysis is commonly reported as the average strain of the element, while the true strain is difficult to obtain.…”

“…The authors have reported on the capability of the SEC to detect fatigue crack on small scale steel compact tension (CT) specimens, and also to localize such cracks leveraging a network configuration [20,21,22] .…”

Dielectric Elastomer Sensors

“…The robust and static characterization of the sensors was demonstrated through testing [47]. Static characterization, dynamic monitoring, localization of fatigue cracks and the distribution of thin film sensor arrays on structures were studied using the referenced SECs [80][81][82][83]. The electrodes of these sensors were composed of SEBS containing carbon black particles, and the sensors were not transparent.…”

Model calibration for a soft elastomeric capacitor sensor considering slippage under fatigue cracks

“…A number of studies [15][16][17] indicated that the SEC sensor could accurately measure strain variation of the detected surface by measuring the capacitance change. To investigate the SEC sensor's performance on fatigue crack monitoring, several fatigue tests haven been conducted with compact tension C(T) specimens [18,19]. Test results have shown that the SEC sensor successfully detected crack growth induced by fatigue loading under a constant load range.…”