Effects of pressure on measurement of strains in EFPI optical fiber sensors embedded in FRP laminates

In the authors' previous study, the internal strain measurement of GFRP laminates by using EFPI optical fiber sensors showed unreliable outputs in a cooling process of an autoclave molding. Its cause seems to be the discrepancy of the optical fiber axis in the optical fiber sensor caused by the molding pressure. In the present paper, compression and shear tests of epoxy specimens where the optical fiber sensor was embedded were conducted to investigate effects of the pressure on the internal strain output. In the experiment, the strain output was monitored under the compressive and the shear load. The stress distributions were calculated by the FEM method to know the pressure applied to the sensor. The relation between the strain output and the calculated pressure on the sensor was obtained. From the results, it was found that the load equivalent to the autoclave molding pressure almost does not affect the strain output.