Uniaxial thermal and/or mechanical deformation-measuring device system and method employing a Bragg grating optical fibre

Uniaxial deformation-measuring device comprising a first section of optical fiber equipped with at least one Bragg grating aligned with the direction of the measurement axis, and a test body subjected to the deformations to be measured, the device being configured to be placed into operating conditions under which the optical fiber is excited by a light wave comprising the Bragg wavelength or Bragg wavelengths with which the at least one Bragg grating is inscribed wherein the first section of the optical fiber is connected to means for reading the Bragg wavelength of each of the at least one grating and comprising demultiplexing means, if the at least one grating includes a plurality of Bragg gratings, the device further comprising:

• a plurality of fixing points, for attaching the first section of the optical fiber to the test body to subject the first section of the optical fiber to a negative, positive or zero preload and of transmitting the elongations of the test body thereto, the fixing points being separated by a distance (Lfib) having a variation (ΔLfib) when the test body is stressed by the deformation to be measured,
• a second section of the optical fiber including a further Bragg grating, the further grating being uncoupled from external mechanical loads to be measured and being subjected to temperatures identical to temperatures to which the at least one Bragg grating of the first section of the optical fiber are subjected, the second section of the optical fiber being configured for the measurement of the mechanical loads causing the deformation of the test body, in order to bring about a compensation of any thermal effects on the measurement,
• wherein:
• the test body has an effective length (Lce) with an elongation (ΔLce) when the test body is stressed by the deformation to be measured, and
• the first section of the optical fiber has a length (Lfib) and a variation in length ΔLfib and the measurement body has an effective length (Lce) such that a longitudinal deformation (ΔLfib/Lfib) of the first section of the optical fiber is strictly greater than an originating deformation (ΔLce/Lce) of the test body, thus defining an amplification factor K that is strictly greater than 1 and is equal to (ΔLfib/Lfib)/(ΔLce/Lce) in a first order.