SHM (Structural Health Monitoring) is not a technique but a set of techniques that are dedicated to monitoring the health of structures during its life time. Such monitoring consists on detecting changes in the material or geometric conditions of the system that may negatively affect its properties.
This process is divided into four levels:
- (1) Determination of the presence of damage in the structure.
- (2) Location of the damage.
- (3) Quantification of its severity.
- (4) Prediction of remaining life of the component or structure.
In order to perform all these actions, it is required having a network of sensors distributed over the test structure and connected to a central system to provide real time information on the status of the component.
Fiber Bragg Grating:
FBG sensors are included in fiber optic lines having a Bragg pattern. The marking of the fiber is performed using a high power UV laser together with a phase mask or interference techniques that establish the desired fringe pattern. The behavior of Bragg sensor is analogous to a filter, e.g., it reflects a specific wavelength of light. The change in the wavelength reflected by the sensor can determine the state of deformation of the structure. The variation in the reflected wavelength can be caused by thermal effects as well; in order to isolate both effects, it is needed the use of a network of sensors instead of a single one.