Disbond detection in a composite honeycomb structure of an aircraft vertical stabilizer by fiber Bragg gratings detecting guided ultrasound waves

Abstract

Efficient and accurate nondestructive inspection systems that save time can benefit scheduled maintenance of aircraft structures. Portable nondestructive inspection techniques capable of scanning larger area structures could find great utility and save considerable time and labor. Contemporary fixed location nondestructive inspection systems, such as the gold standard water-coupled ultrasound imaging by the “squirter” require structural disassembly of the part to be inspected and transportation to/from dedicated location. For large aircraft structures, such as vertical or horizontal stabilizers, this adds weeks to the off-site nondestructive inspection process. An on-site ultrasound detecting method for larger areas, comprising a flexible transducer panel of embedded fiber optic Bragg gratings that is lightweight and portable, and reusable over different structures, is described here. It is shown that this fiber Bragg grating embedded ultrasound transducer panel and readout hardware–software system can map tiny surface displacements of guided wave ultrasound, onsite, over an area of approximately 2 square feet in just over 10 min. The test sample is a sandwich structure with composite skins on both sides of an aluminum metal honeycomb section of an aircraft vertical stabilizer with an artificial engineered disbond. The ultrasound propagation data acquired at 612 positions over the large area, enables in situ nondestructive inspection of defects/ damage by comparing post-damage data with baseline data, and is independent of the material information.

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A Three-Dimensional Vibration Theory for Ultralight Cellular Sandwich Plates Subjected to Linearly Varying In-Plane Distributed Loads

“…It has been demonstrated that gravity has noticeable effects on the precision of positioning systems, inertial navigators, and guided systems as well as the mechanical performance of thin structural elements applicated in aerospace vehicles [4][5][6]. Typically, such thin structural elements include large-scale covering shells/plates of aerospace protection structures, vertical stabilizers of accelerated aircraft or missiles, and structural components of specific systems strongly influenced by varying gravity [7,8]. These structures, relatively thin, are subjected to hyper gravity as the flight vehicle accelerates.…”

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