Investigation of Embedded FBG Response in Polymer Composites: Strain Transfer Mechanism and Interfacial Damage Under Multiaxial Loading

Fiber Bragg gratings (FBGs) embedded in polymer composite materials is a promising method for structural health monitoring (SHM). Conventionally, FBGs are treated as axial strain sensors with a constant sensitivity coefficient, which can lead to significant measurement errors for the multi-axial stress states. This study developed a general framework to calculate the axial strain sensitivity coefficient considering the local multiaxial strain state of the host composite materials, where the analytical strain transfer principle (STP) was integrated with the Opto-mechanical model of FBGs. The responses of embedded FBGs under hydrostatic pressure, biaxial compression, and biaxial tension conditions were validated by the experimental tests. The results further reveal the strong influence of the interfacial bonding state between the FBG and host composite material on the FBG response. This study advances the embedded FBG technology in SHM for composites.