Guided wave mode selection for health monitoring of sub-surface hidden defects on fuel weep holes

Abstract

The in situ health monitoring of defects on the blind side of open holes using ultrasonic plate waves is a challenging problem. Scattering phenomena in this hard-to-inspect region can be used indicate the presence of the defect. This is especially advantageous if these phenomena give rise to the scattering of a wave mode that is unique to the interaction between the incident wave mode and defect. When the defect in question is located within an inaccessible structure, an understanding of how the incident ultrasonic elastic wave field can be scattered from this hidden defect propagates to the accessible surface is important. This paper presents a series of computational investigations to highlight the essential physics that explains the scattering phenomena by a defect located on the blind side of an open hole. The work presented is relevant to the monitoring of defects located in hard-to-inspect regions of future unitized metallic and composite structures. The outcomes advance the knowledge base of inspection of hard-to-access regions with actuators and sensors placed in easily accessible locations.