Abstract
Piezoelectric wafer active sensors (PWAS) are commonly used for detecting Lamb waves for structural health monitoring application. However, in most applications of active sensing, the signals are of high-amplitude and easy to detect. In this article, we have shown a new avenue of using the PWAS transducer for detecting the low-amplitude fatigue-crack related acoustic emission (AE) signals. Multiphysics finite element (FE) simulations were performed with two PWAS transducers bonded to the structure. Various configurations of the sensors were studied by using the simulations. One PWAS was placed near to the fatigue-crack and the other one was placed at a certain distance from the crack. The simulated AE event was generated at the crack tip. The simulation results showed that both PWAS transducers were capable of sensing the AE signals. To validate the multiphysics simulation results, an in-situ AE-fatigue experiment was performed. Two PWAS transducers were bonded to the thin aerospace test coupon. The fatigue crack was generated in the test coupon which had produced low-amplitude acoustic waves. The low-amplitude fatigue-crack related AE signals were successfully captured by the PWAS transducers. The distance effect on the captured AE signals was also studied. It has been shown that some high-frequency contents of the AE signal have developed as they travel away from the crack.
Highlights
We found that the acoustic emission (AE) signals are much weaker than the active structural health monitoring (SHM) signals; the AE
The AE events happen at every cycle as the fatigue crack grows
The advancement of the fatigue crack generates the AE signals at every loading cycle. This indicates the dynamics of near-field Piezoelectric wafer active sensors (PWAS) had a minimal effect on the far-field PWAS with the prescribed that the AE events happen at every cycle as the fatigue crack grows
Summary
Monitoring of the acoustic emission (AE) from the progressive fatigue damage is categorized as the passive online monitoring [5,6,7]. Lee et al experimentally showed that the AE waves from fatigue crack growth propagate as guided waves [8]. They used the commercially available resonant type (250 kHz) and wideband (100 kHz–600 kHz) AE sensors to capture the AE signals. These sensors were designed to effectively measure the out-of-plane wave motion. The AE signals from the fatigue crack are usually low-amplitude signals and challenging to detect using the conventional AE sensors [12,13]
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