Fiber optic distributed strain sensing for open-holes specimen axial tests

We have applied a commercial optical frequency domain reflectometer with high spatial resolution to measure the strain exerted on an aluminum specimen under tensile strength (open hole) test. The strain profile has been measured until failure by means of an optical fiber and by ten standard electric strain gauges. The matching between the measurement data provided by the two techniques at the strain gauges positions is excellent, except in the proximity of the hole, where the strain gradient is maximum. Due to that, a precise correspondence between optical fiber and strain gauges position near the hole is mandatory in order to measure the same strain value. The resolution attainable by the optical system, that has not counterpart in any electrical systems, enables an unprecedented spatial sampling, thus allowing a much better characterization of the strain profile along the sample.