Fatigue crack monitoring in OSDs using Lamb wave longitudinal transmission

Orthotropic steel bridge decks (OSDs) find extensive use in bridge engineering worldwide but suffer from fatigue cracking due to vehicle loads. The technology of Lamb wave longitudinal transmission has potential to monitor fatigue cracks. Experimental and numerical investigations were conducted to examine the impact of wave longitudinal transmission on fatigue crack monitoring, utilizing the lightweight arrangements of Lamb wave sensors. Three full scale specimens of OSDs were manufactured and subjected to testing. The sensors utilizing Lamb waves were continuously monitored two types of cracks that were initiated in tests. Standardized wave features were extracted by a wavelet transform algorithm from the received waves in order to evaluate crack growth. Finite element models was also established and verified by the experimental results. Parametric studies were conducted to investigate the effects of crack types, wave transmission distances, and excitation frequencies on wave features. The experimental results show that the wave features exhibit clear variation trends as both the fatigue life and the fatigue crack lengths increase. The findings of the parametric study reveal the proposed sensor arrangements are proved to be suitable for general application. Meanwhile, the different variations in wave features can be observed in the various crack types and lengths, but they are less noticeable when considering different wave transmission distances, as long as the excitation frequencies remain constant. The approach to improve the signal-to-noise ratio in engineering applications arises from the fact that the monitoring frequency of wave features should be chosen as the same as the excitation frequency.