Theoretical Studies of Temperature Compensation of Results of Diagnostics of Polymer Composites Using the Method of Two Optical Fibers

The paper considers the advantages and disadvantages of existing methods for temperature compensation of data from fiber-optic sensors based on fiber Bragg gratings as part of an embedded system for simultaneous testing of deformation and temperature of polymer composite materials. It is shown that when external temperature testing is impossible, it is most expedient to implement the method of two optical fibers with different sensitivity to at least one of these parameters due to different dopants. Technological issues related to the formation of a spatial topology and the provision of an effective survey of the embedded optical system for monitoring polymer composite materials by the two-fiber method are considered. The results of theoretical research of a linear model of temperature compensation, a model that takes into account the influence of cross sensitivity, as well as a quadratic model of temperature compensation of optical testing data are presented. It has been established that the linear model is the simplest, however, when using it, one should take into account the error associated with the inaccuracy of the approximation of optical inspection data by a linear function. At the same time, it is shown that in order to improve the quality and reliability of the results of optical testing, it is advisable to use a quadratic model of temperature compensation, which provides an error level comparable to the error of the fiber-optic sensor survey device. The results obtained can be used to develop methods for the simultaneous testing of samples, as well as monolithic and three-layer structures from structural layered polymer composite materials with limiting molding conditions (temperature less than 180°C, specific pressure lower than 0.7 MPa), as in the process of bench and other tests, and, in the future, in real operating conditions.