Monitoring and verification of micro-strain generated inside the laminate subjected to thermal loading through fiber bragg grating sensors and classical laminate theory

Abstract

Fiber Bragg Grating (FBG) sensors possess enormous potential for the cure monitoring and integrity assessment of Carbon Fiber Reinforced Polymer (CFRP) composites. These sensors can be embedded inside the structure to monitor the strain in the desired region of interest. The strain on an FBG sensor can be calculated by measuring the change in the center wavelength of the sensor. This change in center wavelength is a function of temperature and mechanical strain. Therefore, temperature compensation is necessary for a precise mechanical strain measurement with an FBG sensor. In this study, FBG sensors are embedded in different layers of the CFRP laminate to record the mechanical strain caused by the thermal expansion, which happens under the influence of temperature. Classical laminate theory (CLT) is implemented to assess the accuracy of FBG sensor measurements and the strain data acquired from both FBG sensor and CLT correlates. Furthermore, a resistive strain gauge is deployed to measure the strain under the influence of temperature. It is depicted that strain values recorded by the strain gauge under the influence of the temperature do not agree with the strain measured by CLT, and an error of 150% occurs among their values.