Lamb Wave–Based Structural Health Monitoring for Aluminum Bolted Joints with Multiple-Site Fatigue Damage

Abstract

In this paper, the Lamb wave based structural health monitoring for aluminum bolted joints with multiple-site fatigue damages was investigated experimentally. In the experiments, the Lamb waves were generated and received by piezoelectric transducers. Three specimens were prepared for fatigue testing and monitored by the Lamb wave signals. Due to the complex geometry of the specimen, multiple fatigue cracks were observed at different bolt holes during the fatigue testing. The signals before and after the initiation of the fatigue cracks were compared to calculate the damage index (DI). In general cases, DI can serve an indicator to map the fatigue crack size. In the experiments, it was found that the phase shifts between the baseline signal before fatigue crack initiates, Sb(t), and the signal with fatigue cracks, S(t), can result in an overestimated DI. To solve this problem, the envelope damage index (EDI) was introduced to monitor the fatigue cracks. The envelope curves of Sb and S are considered in the calculation of EDI. In the experiments, three specimens were prepared for fatigue testing. Crack-size observations of the specimens indicated that the EDI is a better parameter than DI for monitoring the fatigue crack size and location.