No abstract

Diaphragm-type couplings are high misalignment torque and speed transfer components used in aircrafts. Crack development in such couplings, or in the drive train in general, can lead to component failure that can bring down an aircraft. Real time detection of crack formation and growth is important to prevent such catastrophic failures. However, there is no single Nondestructive Monitoring method available that is capable of assessing the early stages of crack growth in such components. While vibration based damage identification techniques are used, they cannot detect cracks until they reach a considerable size, which makes detection of the onset of cracking extremely difficult. Acoustic Emission (AE) can detect and monitor early stage crack growth, however excessive background noise can mask acoustic emissions produced by crack initiation. Fusion of the two mentioned techniques can increase the accuracy of measurement and minimize false alarms. However, a monitoring system combining both techniques could prove too large and heavy for the already restricted space available in aircrafts.In the present work, we will present a newly developed integrated Acoustic Emission/Vibration (AE/VIB) combined sensor which can operate in the temperature range of -55°F to 257°F and in high EMI environment. This robust AE/VIB sensor has a frequency range of 5 Hz-2 kHz for the vibration component and a range of 200-400 kHz for the acoustic emission component. The sensor weight is comparable to accelerometers currently used in flying aircraft. Traditional signal processing approaches are not effective due to high signal attenuation and strong background noise conditions, commonly found in aircraft drive train systems. As an alternative, we will introduce a new Supervised Pattern Recognition (SPR) methodology that allows for simultaneous processing of the signals detected by the AE/VIB sensor and their classification in near-real time, even in these adverse conditions. Finally, we will discuss the architecture developed to produce a fully autonomous monitoring tool based on the fusion of the AE and Vibration techniques.

Acoustic Emission (AE) monitoring was performed during Pseudo-Dynamic Testing of a torsionally unbalanced, two-storey, one-by-one bay reinforced concrete frame structure. The structure represented a 0.7-scale model of a real-size frame structure designed and detailed according to the standards prevailing in Greece in 60's, without engineered earthquake resistance. Real time monitoring of AE activity versus the complex applied load resulted in semi quantitative damage characterization as well as comparative evaluation of the damage evolution of the different size columns. Evolution of the AE energy rate per channel, as revealed from zonal location, and the energy rate of linearly located sources enabled the identification of damage areas and the forecast of crack locations before cracks were visible with naked eye. In addition to that, the results of post processing evaluation allowed for the verification of the witnessed damaged areas and formed the basis for quantitative assessment of damage criticality.