The performance of two complementary optical strain measurement techniques, speckle shearing interferometry (shearography) and fibre Bragg grating (FBG) sensors, is compared with that of resistance foil strain gauges (RFSGs) and with theoretical predictions. The test object used for the surface strain measurements was a hydrostatically loaded ABS pipe. A multi-component shearography instrument, capable of full surface strain measurement, was used to determine the displacement gradient components, from which the surface strain components were calculated. Six surface mounted wavelength division multiplexed FBG sensors were used to measure the axial and the hoop strains. RFSGs located on the surface of the pipe, adjacent to the FBGs, were used for comparison. Reasonable agreement between theory and the axial and hoop strains determined by the different techniques was found. Issues associated with deploying and comparing the techniques are discussed.

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Both sensing techniques, FBG wavelength shift and FCG intensity change, were applied in a train axle counting system. They turned the dynamic strain of rail track into accurate axle numbers of passing trains.

A displacement monitor with deforming ring is developed to ensure the FBG suspended and to avoid it to be chirped by covering glue. The mechanical analysis provides ring size to ensure suitable BFG wavelength shift extent within detected range. Two pieces of FBG are crosswise fixed on the ring and pre-drawn properly. Rail creep force of high speed railway makes one tense, the other compress. To add these two wavelength shifts, the sensitivity is doubled, and environmental temperature interference is eliminated. Its general error is ±0.25% FS; repeatability is 0.2% FS; resolution is 0.1mm; the temperature error, from -20 to 60Cº, is ±0.45mm in 50mm range.

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