Abstract
Guided wave detection using different fiber optic sensors and their applications in damage detection for composite laminates were systematically investigated and compared in this paper. Two types of fiber optic sensors, namely fiber Bragg gratings (FBG) and Doppler effect-based fiber optic (FOD) sensors, were addressed and guided wave detection systems were constructed for both types. Guided waves generated by a piezoelectric transducer were propagated through a quasi-isotropic carbon fiber reinforced plastic (CFRP) laminate and acquired by these fiber optic sensors. Characteristics of these fiber optic sensors in ultrasonic guided wave detection were systematically compared. Results demonstrated that both the FBG and FOD sensors can be applied in guided wave and damage detection for the CFRP laminates. The signal-to-noise ratio (SNR) of guided wave signal captured by an FOD sensor is relatively high in comparison with that of the FBG sensor because of their different physical principles in ultrasonic detection. Further, the FOD sensor is sensitive to the damage-induced fundamental shear horizontal (SH0) guided wave that, however, cannot be detected by using the FBG sensor, because the FOD sensor is omnidirectional in ultrasound detection and, in contrast, the FBG sensor is severely direction dependent.
Highlights
Conventional ultrasonic inspection of large structures is very time-consuming because the transducer needs to be scanned over each point of the structure to be tested
Setup of the ultrasonic detection system using laser Doppler velocimeter (LDV) and the spiral FOD sensor is schematically shown in Figure 4, in which the light source is He-Ne laser and heterodyne interference technique is applied to the measurement
To ensure that the guided wave signals are acquired under the same excitation circumstance for the same specimen, experiments for one specimen were done under three procedures: 1) acquiring guided wave signal using FOD sensor; 2) removing the FOD sensor from the specimen and bonding fiber Bragg grating (FBG) sensor at the same position as the FOD sensor; 3) acquiring guided wave signal using the FBG sensor
Summary
Conventional ultrasonic inspection of large structures is very time-consuming because the transducer needs to be scanned over each point of the structure to be tested. An ultrasonic wave can be detected through an optical filter processing of the light reflected from FBG sensor. The other is a system has a tunable laser source in which the intensity of the light reflected from FBG sensor corresponds directly to the ultrasonic response [20,21]. Two ultrasonic detection systems for the purpose of guided wave and damage detection are presented, which are based on the FBG and FOD sensors, respectively. The extracted signal features were compared to systematically disclose the characteristics of the FBG and FOD sensors in guided wave and damage detection for CFRP laminates.
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