Abstract
Adhesive and its aging can have influence on the Piezoelectric (PZT) elements in structural health monitoring (SHM) systems. However, the current research pays little attention to the effect of adhesives in SHM systems, and the mechanism of adhesive aging on monitoring signals is still unclear. In the present study, the relationship between types of adhesives, adhesive thickness, accelerated aging, and monitoring signal was analyzed in detail. The study was carried out with three kinds of epoxy resin AB adhesive (AW106, E-30CL, and E-120HP) and bonding thicknesses (0.01, 0.05, and 0.12 mm), and the elevated temperature was 100 °C for 45 days. The signal-based monitoring method was used to extract the characteristic parameters. The experimental results indicated that the standard shear strength and thickness of the adhesive may have a combined effect on the monitoring signal. Increasing the thickness may enhance the shear strength between PZT and the matrix. For the effectiveness of monitoring the signal propagation, however, increase in thickness may have a negative influence. Moreover, the elevated temperature will bring the signal amplitude to a peak in the first period of aging, and the highest point appears in 10 to 15 days. Nevertheless, with the increase of aging time, the adhesive will finally be degraded, resulting in the decrease of the signal amplitude. The experimental results may provide useful information for practical monitoring in the SHM field.
Highlights
There has been growing interest in structural health monitoring (SHM) technology for online structural health monitoring and damage control, which is widely used in aerospace and civil engineering, machinery, transportation, and other fields [1,2]
Based on the previous research works [15,28,29], we find that the type of adhesive used has an influence on the monitoring signal in the SHM system
As can be seen from the figure, the influence of adhesive type on the monitoring signal varies according to the thickness
Summary
There has been growing interest in structural health monitoring (SHM) technology for online structural health monitoring and damage control, which is widely used in aerospace and civil engineering, machinery, transportation, and other fields [1,2]. The influence of sensor/structure bonding defects was studied by Lamb wave propagations and impedance methods, and the results showed a significant change of the phase and amplitude of the propagated waves and impedance spectrum. Few studies have comprehensively considered the influence of shear strength, thickness, and aging of adhesives between piezoelectric discs and aluminum substrate on the signal; as such, the change trend of different thickness and type of adhesive in the aging progress is not certain. We performed a system experimental study to investigate the effects of adhesive and bonding thickness on the monitoring signal of the SHM system. This work considered the signal-based damage monitoring approach to extract the characteristic parameters of the Lamb wave, which are the normalized amplitude and phase difference of A0 mode. The influence of adhesive and its aging on receiving signal was analyzed
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