Abstract
Lamb wave (LW) is well suited for structural health monitoring (SHM) in advanced composites. However, characteristic differences between the symmetric modes and the anti-symmetric modes often add complexity to SHM systems. The anisotropic nature of composite materials, on the other hand, necessitates direction-sensitive sensing. In this paper we report the experimental demonstration of bidirectional (0° and 90°), bimodal (S0 and A0) LW measurement within the frequency range of 20–140 kHz using a polarization-maintaining fiber Bragg grating (PM-FBG) sensor attached to a composite laminated plate. By selectively interrogating the fast and/or the slow axis of the PM-FBG, we show that not only can the sensor respond to LWs propagating along both directions, but the response can also be used to differentiate the two directions. Moreover, the fast axis of the sensor is able to respond to both the S0 and the A0 modes when the sensor is aligned with the wave propagation direction, whereas single S0 mode response can be achieved with the slow axis operating perpendicularly to the wave propagation direction. Such diverse responses indicate the potential of PM-FBGs as versatile multi-parameter SHM detectors, which can effectively address the challenges posed by material anisotropicity and LW mode diversity.
Highlights
Lamb waves (LWs) have been widely studied in the field of structural health monitoring (SHM)for damage detection in various structures such as pipes, rails, containers, and vessels [1,2,3,4,5]
Composite materials post a different challenge to SHM
In the work reported here, we extended the concept of multi-parameter sensing (MPS) into LW sensing and explored the potential of polarization-maintaining fiber Bragg grating (PM-fiber Bragg grating (FBG)) as bidirectional, mode-selective LW sensors
Summary
Lamb waves (LWs) have been widely studied in the field of structural health monitoring (SHM)for damage detection in various structures such as pipes, rails, containers, and vessels [1,2,3,4,5]. Lamb waves (LWs) have been widely studied in the field of structural health monitoring (SHM). LWs can travel over long distances and are highly sensitive to structural damage [3]. The two modes exhibit drastically different characteristics and are suitable for different types of damage inspections [5,11]. Composite materials post a different challenge to SHM. Since hybrid laminates such as carbon fiber reinforced polymer (CFRP) are usually highly anisotropic, the propagation characteristics of LWs, including velocity, dispersion, mode coupling and attenuation, display a strong directional dependency in such materials [11,19,20]. A large number of actuators and sensors are usually required to form a distributed array for accurate
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