Three-dimensional finite element modelling of ultrasonic-guided wave scattering from fuel weep holes

Abstract

A three-dimensional finite element model for analysis of ultrasonic-guided wave scattering from a hidden notch on a through-thickness circular hole is presented in this article. The structure is representative of an aircraft wing spar with a fuel weep hole. In contrast to the high-frequency bulk-wave wedge transducer methodology traditionally used for weep hole inspection, the length scales of the in situ technique are such that the wavelength of the incident guided waves are comparable with the hole diameter and larger than the defect length. The ability to accurately model acousto-ultrasonic elastic wave dynamics is crucial for future developments in this research field. Three-dimensional laser vibrometry is used to measure the deformation of a low-profile surface-bonded piezoelectric disc. The measurements provide the input conditions for a force-actuated computational model. The computational scattered wave field from a notch on the blind side of the hole is compared with experimental data for model validation. It is concluded that the boundary conditions for wave scattering from the hidden notch are a complex combination of the incident wave field and the dispersive edge-guided Rayleigh-type flexural wave that is formed on the free surface of the hole.