High Frequency Quantitative Photoelasticity Applied to Jet Engine Components

Abstract

For sometime, reflection photoelasticity has been used in a qualitative manner as an aid to the placement of strain gauges in vibration tests on turbine and compressor blades. Often, the motivation for such tests is the validation of numerical models used in life-time predictions. Strain gauges supply data at a small number of discrete points, whereas the photoelastic fringe patterns provide information over the whole field of view. Digital photoelasticity based on phase-shifting allows these fringe patterns to be processed into maps of surface strain data that can be used to verify the computational results. Digital photoelasticity has been developed over the last two decades utilising spectral or phase approaches sometimes combined with Fourier analysis; and in most reported applications only idealised case studies are considered. Recently, the application of digital photoelasticity in high frequency blade tests has been developed as a robust methodology that can be applied using standard equipment or using solid-state polariscopes. The paper includes descriptions of the methodology and exemplar results to demonstrate the efficacy of this advanced application of photoelasticity for full-field validations of numerical modelling.