Comparison of optical fibre Bragg grating strain sensors with shearography and resistance foil strain gauge measurements

Abstract

ABSTRACT Optical fibre Bragg grating (FBG) strain sensor measurements were compared with theoretical strain calculations and measurements from two competing techniques: shearography and resistance foil strain gauges (RFSG). Axial and hoop strains in an ABS pipe, loaded by ch anging the internal pressure were investigated. Six wavelength-multiplexed FBG sensors were used to measure the axial and the hoop strains. RFGSs located on the surface adjacent to the FBGs were used for comparison. A multi-component shearography instrument was also used to perform full-field surface strain measurements on the pipe. Measurements were made using two shear directions, yielding six displacement gradient components in total. The measured Gu/Gx and Gv/Gy components were compared with theoretical hoop and axial strains respectively. Good agreement was found between the three techniques and the theory. Keywords: optical fibre Bragg gratings, shearography, strain measurement 1. INTRODUCTION Modern manufacturing techniques increasingly require advanced techniques for the characterisation of surface strain, for example in materials with anisiotropic properties, such as composites, for the investigation of objects with complex shape, and for strain measurement in components lightened to improve efficiency. This paper addresses the calibration of two such advanced optical techniques: optical fibre Bragg gratings (FBGs) and shearography. FBG sensors have been demonstrated previously for a range of strain measurement applications