Load-Differential Features for Automated Detection of Fatigue Cracks Using Guided Waves (Preprint)

摘要

Guided wave structural health monitoring (SHM) is being used to assess the integrity of plate-like structures for aerospace, civil and mechanical applications. Prior research has investigated how guided wave propagation is affected by applied loads, which induce anisotropic changes in both dimensions and phase velocity. In addition, it is well-known that applied tensile loads open fatigue cracks and thus enhance their detectability using ultrasonic methods. Here we introduce a class of load-differential methods in which signals recorded from different loads at the same damage state are compared without using previously obtained damage-free data. Changes in delay- and-sum images are considered as a function of differential loads. Load- differential features are extracted from these images that capture the effects of loading as fatigue cracks are opened. Damage detection thresholds are adaptively set based upon the load-differential behavior of the various features, which enables implementation of an automated fatigue crack detection process.