Research and Development: Applications

Context: Guided waves (GW) based monitoring is seen as one of the most promising structural health monitoring (SHM) techniques for damage detection in plate like structures. Most GW based SHM techniques quantify difference between the healthy and damaged condition of the structure. The healthy baseline is not always available or corrupted with noise or ambient condition changes. The reference-free SHM techniques allow to overcome this. Very little work in this area has been carried out thus far. During the investigations in the ongoing Opus 17 project some properties of fiber Bragg grating (FBG) sensors for GW measurements were revealed which open up the possibility of the use of FBG sensors for reference-free SHM and is the main motivation of the project. The project proposes a three level intervention strategy to achieve GW based reference-free SHM using FBG sensors. The project also aims at integrating the three level interventions into a single methodology and improving the performance of the method through sensor placement optimization.
Objectives:
O1. Study the use of polarization maintaining (PM)-FBG for separating the Symmetric (S) and Antisymmetric (A) waves and reference-free damage detection
O2. Development of novel signal processing techniques for instantaneous baseline based techniques
O3. Study of the use of self-referencing feature of remote bonded FBG sensors for damage localization
O4. Study different configurations of bonds and sensors in order to expand the methodology in spatial domain
O5. Study the robustness of the methodology under changing ambient temperature conditions
O6. Combine the three intervention strategies for optimal performance for reference-free damage detection
O7. Development of optimization of placement for FBG sensors for improved damage assessment
Methodology: This project aims at developing GW based reference-free SHM strategies using FBG sensors. The project proposes a three stage intervention to achieve the reference-free SHM. The interventions will be at hardware level, advanced signal processing level and configuration level. The hardware level intervention is, through the use of PM-FBG sensors which allow separation of A and S modes which can then in turn be used to detect the mode conversion which may be used for reference-free SHM. The advanced signal processing intervention is through development of instantaneous baseline approach for use with FBG sensors. Different factors specific to the use of FBG sensors will be studied and then used to compensate for the differences. The configuration level intervention will be through the use of self-referencing feature which is offered by the FBG sensors. The self-referencing feature has been shown to detect damage but needs to be extended for reference-free SHM and also for damage localization. In addition to the three level intervention, a key task will be to integrate the three approaches and improve their performance through the optimization of the SHM system including placement of the sensors. The scope of the studies includes numerical, analytical and experimental study on both composite and metallic plate-like structures.
Innovation:
I1. Use of PM-FBG sensors for A and S mode separation and their use for reference-free damage detection.
I2. Customize the instantaneous baseline techniques for FBG sensors
I3. Develop methodology for damage localization using self-referencing GW based SHM
I4. Development of sensor and bond configuration for extension of self-referencing and instantaneous baseline based techniques in the spatial domain
I5. Integration of the three promising reference-free damage detection approaches for a robust SHM system
I6. Optimization of sensor placement for GW based SHM using FBG sensors taking into consideration the constraints and advantages of the FBG, and demands of reference -free damage detection methods
Impact
* Development of reference-free SHM method which allows wider applicability
* Use of mode separation to simplify the signal processing
* Development of instantaneous baseline methodology which gives robustness to the SHM in changing ambient conditions
* An optimization methodology tailored for reference-free SHM as well as based on the functional constraints of the FBG sensors.