Nawasra, Jawad (2009) Novel techniques for high-speed time-resolved photoelestic stress analysis and its application to compressor blade design. PhD thesis, University of Warwick.

Abstract

This thesis investigates the application of quantitative, optical non-contact techniques to time varying stress fields to obtain time-resolved full-field measurements of stress and strain. Available optical techniques are reviewed and a specific case developed for the use of Photoelastic stress analysis (PSA). As a result of this research two novel developments in PSA are presented, including an industrially robust coating material technology and methods for high-speed acquisition of transient stress fields. These developments extend the potential applications of PSA and simplify the procedures involved. A novel birefringent electrolytic coating is presented and calibrated to demonstrate its potential as a practical photoelastic coating. The 20 m thickness coating is characterised and shown to behave linearly with strain. The coating also shows potential for application in plastic and non-linear photoelastic measurements. Several types of anodising and sealing treatments are compared, focusing on their relative sensitivity. The strain-optical coefficient (K) is derived for four thicknesses of decorative sulphuric acid anodising allowing qualitative and quantitative data to be extracted. Two time-resolved photoelastic techniques capable of measuring high(kHz) and low(Hz) frequency transient stress fields are described and demonstrated. Both techniques are based on a concept of a `Multiple View Polariscope', where the phase steps are captured simultaneously from multiple views. The configurations include a planar multi-camera method and a single camera with a modified `Quadrant' lens. As part of a collaborative study, compressor blade geometries were generated based on an existing Rolls-Royce component. The potential of the high-speed Multiple View Polariscope is demonstrated by the application to the compressor blades, which are subjected to a dynamic impact load to simulate domestic object damage. The resulting quantitative time-resolved stress fields allowed the performance of each blade to be compared against the original component. This investigation has shown the potential for general robust optical tools for industrial quantitative applications of residual, static and dynamic stress measurement.

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