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

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 changing 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 delta u/delta x and delta v/delta y components were compared with theoretical hoop and axial strains respectively. Good agreement was found between the three techniques and the theory.