Composite materials are becoming increasingly more valuable due to their high specific strength and stiffness. Currently, most components are operated for a number of service cycles and then replaced regardless of their actual condition. Embedded fiber Bragg gratings are under investigation for monitoring these components in real time and estimating their remaining life. This article presents research conducted on a novel technique for prediction of the remaining life of composites under fatigue loading using embedded fiber Bragg grating sensors. A prediction is made of the remaining life at every cycle based on data collected from the sensors and the previous loading history.

A structural health monitoring (SHM) study of biaxial glass fibre-reinforced epoxy matrix composites under a constant, high strain uniaxial fatigue loading is performed using fibre Bragg grating (FBG) optical sensors embedded in composites at various locations to monitor the evolution of local strains, thereby understanding the damage mechanisms. Concurrently, the temperature changes of the samples during the fatigue test have also been monitored at the same locations. Close to fracture, significant variations in local temperatures and strains are observed, and it is shown that the variations in temperature and strain can be used to predict imminent fracture. It is noted that the latter information cannot be obtained using external strain gages, which underlines the importance of the tracking of local strains internally.

The significance of strain measurement is obvious for the analysis of Fiber-Reinforced Polymer (FRP) composites. Conventional strain measurement methods are sufficient for static testing in general. Nevertheless, if the requirements exceed the capabilities of these conventional methods, more sophisticated techniques are necessary to obtain strain data. Fiber Bragg Grating (FBG) sensors have many advantages for strain measurement over conventional ones. Thus, the present paper suggests a novel method for biaxial strain measurement using embedded FBG sensors during the fatigue testing of FRP composites. Poisson’s ratio and its reduction were monitored for each cyclic loading by using embedded FBG sensors for a given specimen and correlated with the fatigue stages determined based on the variations of the applied fatigue loading and temperature due to the autogenous heating to predict an oncoming failure of the continuous fiber-reinforced epoxy matrix composite specimens under fatigue loading. The results show that FBG sensor technology has a remarkable potential for monitoring the evolution of Poisson’s ratio on a cycle-by-cycle basis, which can reliably be used towards tracking the fatigue stages of composite for structural health monitoring purposes.

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In this study, failure modes of foam core sandwich composites are investigated by using embedded Fiber Bragg Grating sensors. Sandwich specimens with Fiber Bragg Grating sensors, embedded inside the face sheet, are manufactured using vacuum infusion process and then subjected to a static and a cyclic loading under the three-point bending mode. Different failure modes are monitored utilizing the wavelength shift and the spectrum of Fiber Bragg Grating sensors. It is shown that the responses of the Fiber Bragg Grating sensor differ depending on damage modes thereby making structural health monitoring of sandwich structures possible.