In this study, a structural health monitoring (SHM) fastener consisting of a conformable eddy current sensor film that is integrated with a metallic sleeve that goes around the fastener shank was developed for in situ monitoring of fatigue cracks at hole locations in layered metallic joints. Integration of sensors with the fastener shank is an optimal methodology for embedding sensors to detect cracks, which most commonly initiate at bolt-hole boundaries in metallic airframe components. The sensors are located in proximity to the bolt-hole boundary through the entire joint stack up, enabling detection of cracks on inner joint layers, which are otherwise inaccessible and cannot be detected with traditional surface-mounted SHM technologies. An additive, interleaved, multilayered, electromagnetic (AIME) sensor was designed for this application. The sensor's salient qualities are an enhanced capability to inspect adjacent joint layers with high degrees of liftoff, or separation between sensor and joint layer, and a capability to track cracks out to great depth as they propagate from a through-hole boundary. The analysis and design of the sensor film and sensor/fastener system are presented herein followed by an experimental validation of the complete SHM system.

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This paper presents a novel Fiber-Bragg Grating interrogation system and its validation for detection of Lambwaves and acoustic emission events on both aluminum and composite substrates. The system utilizes a robust laser demodulation technique for FBG interrogation, based upon a simple laser wavelength tracking scheme. This technique enables detection of much higher frequency strains than previous FBG interrogation techniques, enabling the use of FBG sensors in acousto-ultrasonic structural health monitoring schemes such as Lamb-wave pitch-catch and acoustic emission detection in the presence of a quasistatic strain background. The principles of the FBG interrogation system are presented, including validation of the system for detection of ultrasonic Lamb waves, and results from a 4-point bending test of a braided composite tube wherein the FBG system was used to detect crack-growth induced AE events on the braided tube. The AE data agreed well with damage index values measured by a commercial acousto-ultrasonic system.

This paper presents a case study of a root cause failure analysis of a 373 MW (nominal) steam turbine generator that exhibited both “reversible” and “irreversible” thermal sensitivity vibratory behavior, as well as reduced output, resulting from a unique rotor winding insulation failure mode. An analysis of the historical vibration behavior of the generator is presented along with the techniques applied to diagnose the source of vibration, which included flux-probe testing, full-speed varied-load vibration diagnostics, and an inspection of the rotor field winding followed by a full-field rewind. These techniques allowed for an in-situ root cause analysis, which proved effective in reducing the generating unit’s disassembly, repair and reassembly time, and assuring the steam turbine’s availability for the peak seasonal electric period.