Thesis
An investigation into the reliability of thermosonics for aero engine turbine blade inspection
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2013
- Thesis identifier
- T13473
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- Turbine blades in gas turbine engines are liable to fatigue cracking due to the harsh conditions in which they operate. The current non-destructive testing (NDT) method for inspecting these blades for cracks is Fluorescent Penetrant Inspection (FPI). However, extensive chemical cleaning of the blades is required for FPI to be effective. This pre-inspection cleaning process is expensive and time-consuming. A reliable and rapid NDT screening method that could detect cracked blades prior to cleaning would reduce the number of blades going through the mandatory cleaning and FPI inspection, thus saving cleaning and inspection costs. Thermosonics has been proposed as a suitable candidate for this NDT screening. In thermosonics, an ultrasonic horn is used to vibrate a component, and if a crack is present, the vibrating crack generates heat which is detected by an observing infra-red (IR) camera. Although thermosonics is capable of detecting defects in several types of components, its reliability remains uncertain due to lack of repeatability of the excitation and the non-uniform nature of the vibration field excited in the component. This Thesis investigates the reliability of thermosonics as a rapid screening technique on Rolls-Royce turbine blades. First, an empirical study was conducted to optimise the thermosonic technique developed for this project, after which the reliability of the technique was assessed on a large set of turbine blades with known cracks. The developed technique was shown to be robust and capable of detecting cracks in the blades. However, the non-repeatability of the excitation was evident in the empirical study. Researchers at Imperial College have proposed a vibration monitoring tool called the Heating Index (HI) to mitigate the non-repeatability issue with the excitation. The HI was assessed in this Thesis to determine its reliability on turbine blade thermosonic inspection. The HI was found to be useful for cases where a crack was known to be present, but not for a realistic case where the presence of a crack is unknown. An alternative vibration monitoring parameter (A2) was proposed and found to compare favourably with the HI parameter. Importantly, the A2 parameter can be used without prior knowledge of the presence of a defect. Finally, a methodology was proposed to simulate the full-field vibrational response of a turbine blade under thermosonic excitation. The results from this work demonstrated the non-uniformity and complex vibrational energy field excited in a typical thermosonic test. In addition, the vibrational energy distribution across a blade for a typical thermosonic test is presented.
- Resource Type
- Note
- Strathclyde theses - ask staff. Thesis no. : T13473
- DOI
- Date Created
- 2013
- Former identifier
- 991203
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