The Study of the Directional Sensitivity of Fiber Bragg Gratings for Acoustic Emission Measurements

Structural health monitoring (SHM) of engineering structures plays a crucial role in ensuring their safety and integrity. Acoustic emissions (AE) can be one of the several ways to monitor the structural health. Fiber Bragg grating (FBG)-based AE measurement technique is emerging as a solution to assess cracks in structures remotely and has advantages of being less bulky and having low noise, high bandwidth and ease of implementation. This paper presents a study on the impact of AE signals on FBGs attached to a substrate, focusing on the directional sensitivity using different configurations. For ease of installation, the FBG sensors are metallically packaged similar to lead zirconium titanate (PZT) sensors in which they can withstand temperatures of up to 250 degrees C. The directional AE sensitivity of the packaged FRG sensor device is studied and compared with that of a surface attached FBG. Experimentally, the AE signals are generated by a metal ball drop impact on aluminum plate and are measured using an FBG AE interrogation system. A numerical simulation of the design was carried out using ANSYS explicit dynamics and the AE wave propagation in structure was analyzed and experimentally verified.