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Highlights • Incremental Lamb wave scattering from a notch emanating from a through-hole is analyzed. • Multiple frequencies and hole diameters are considered as well as a notch with no hole. • Numerical results are validated with experimentally measured scattering patterns. • The presence of even a small hole significantly affects notch incremental scattering. • Incremental scattering from off-angle incident waves is a strong function of frequency. Abstract Lamb wave scattering from a crack originating at a through-hole is of practical importance because of the abundance of fastener holes used in engineering structures. Notches are often used to simulate cracks so that Lamb wave methods can be more conveniently investigated in the laboratory. A linear, three-dimensional finite element model is employed in this paper to study incremental scattering of the fundamental anti-symmetric (A 0 ) Lamb wave mode from notches emanating from through-holes. The term “incremental scattering” refers to the change in scattering caused by introduction of the notch and is motivated by structural health monitoring for which transducers are fixed and signal changes are interpreted to detect damage. Far-field angular scattering patterns are generated for multiple incident angles and frequencies, and such patterns are experimentally validated at one frequency by laser vibrometry measurements. Comparisons are made between a vertical notch alone (no hole) and notches located above and below the through-hole. Additionally, holes of different sizes are considered to investigate the effect of hole diameter on incremental scattering patterns. Results show that the presence, location and size of the through-hole affect both the shape and strength of notch incremental scattering patterns. [ABSTRACT FROM AUTHOR]

The scattering of high frequency guided ultrasonic waves by a fatigue crack at the side of a fastener hole has been studied. The guided wave pulse consists of the superposition of the two fundamental Lamb modes A 0 and S 0 above the cut-off frequencies of the higher modes. The scattered field was simulated using a three-dimensional finite difference algorithm with a staggered, Cartesian grid for the limited area of interest around the hole and an analytical phase angle correction for the additional, variable propagation distance. Experimentally, the modes were selectively excited using a standard ultrasonic wedge transducer and measured using a laser interferometer, resulting in good spatial resolution. The scattered field was measured and simulated for an undamaged hole, a small, part-thickness quarter-elliptical fatigue crack, and a through-thickness fatigue crack. Good agreement was found and a significant influence of the fatigue cracks on the scattered field was observed. The complex difference of the scattered field due to additional scattered waves at the fatigue cracks of variable depth and length was evaluated. This allows for the prediction of high frequency guided wave sensitivity for fatigue crack detection at fastener holes, a significant maintenance problem for ageing aircraft. [ABSTRACT FROM AUTHOR]