Structural Health Monitoring in Composite Structures by Fiber-Optic Sensors

Abstract

Fiber-optic sensors cannot measure damage; to get information about damage from strain measurements, additional strategies are needed, and several alternatives are available in the existing literature. This paper discusses two independent procedures. The first is based on detecting new strains appearing around a damage spot. The structure does not need to be under loads, the technique is very robust, and damage detectability is high, but it requires sensors to be located very close to the damage, so it is a local technique. The second approach offers wider coverage of the structure; it is based on identifying the changes caused by damage on the strain field in the whole structure for similar external loads. Damage location does not need to be known a priori, and detectability is dependent upon the sensor’s network density, the damage size, and the external loads. Examples of application to real structures are given.

Optimal Preventive Maintenance of Wind Turbine Components with Imperfect Continuous Condition Monitoring

“…According to the authors of [38], ultrasonic methods allow for the identification of cracks, several mm in size. Nowadays, optical fiber sensors are widely used in different structural health monitoring systems [46][47][48][49][50][51]. The use of an online monitoring system based on Brillouin optical time-domain analysis allows for detecting a crack as small as 1.5 cm, when monitoring a wind turbine blade [52].…”

Damage Detection of CFRP Stiffened Panels by Using Cross-Correlated Spatially Shifted Distributed Strain Sensors

“…In this case, differently from the test executed on PNL1, the panel PNL2 is now solicited, just after the impact, by a 3-p (three point) bending load up to 80 N. The quasi-static time history is logged during the solicitation at a fixed sample rate of 10 Hz. The DI is again evaluated according to Equation (3). The DI distribution is reported in Figure 14 where the TL is also provided.…”

Distributed modular temperature-strain sensor based on optical fiber embedded in laminated composites

“…This technology actually allows monitoring some given physical variables (e.g. strain) using a single optical fiber over tens of kilometers, thus enabling continuous distributed monitoring of large composite structures [14][15][16]. However, embedding a very small and brittle optical fiber inside CFRP structures is a time-consuming process [17,18], and, moreover, it typically results in very low survival rates.…”