Effects of high-amplitude low-frequency structural vibrations and machinery sound waves on ultrasonic guided wave propagation for health monitoring of composite aircraft primary structures

• Published in: Journal of sound and vibration 2020-06, Vol.475, p.115289, Article 115289
• Main Authors: Ochôa, Pedro A., Groves, Roger M., Benedictus, Rinze
• Format: Article
• Language: English
• Subjects: Aircraft primary structure; Amplitudes; Composite materials; Diagnostic systems; Impact analysis; Impact damage; Low-frequency vibration; Noise propagation; Propagation; Sound propagation; Sound waves; Structural damage; Structural health monitoring; Time domain analysis; Ultrasonic guided wave; Vibration; Wave dispersion; Wave groups; Wave propagation
• ISSN: 0022-460X; 1095-8568
• DOI: 10.1016/j.jsv.2020.115289

A reliable damage diagnostic by ultrasonic guided wave (GW) based structural health monitoring (SHM) can only be achieved if the physical interactions between wave propagation, the SHM system and environmental factors are fully understood. The purpose of this research was to gain knowledge about the effects of high-amplitude low-frequency structural vibrations (HA-LFV) and audible sound waves (SW) on ultrasonic GW propagation. Measurements were performed on a stiffened panel of a full-scale composite torsion box containing barely visible impact damage. Time-domain analysis of the filtered GW signals revealed that the main effect of HA-LFV was the presence of coherent noise. This was interpreted as the consequence of superposition of multiple dispersive wave groups produced by mode conversion at the moment of reflection on the corrugated panel surfaces during propagation. It was also observed that the coherent noise amplitude depends on the amplitude of the HA-LFV, and on the ratio between the HA-LFV frequency and the ultrasonic excitation frequency. These relationships can potentially be explored for the development of a HA-LFV compensation mechanism to enable in-service GW based damage diagnostics. In contrast, GW signals in the cases with audible SW present were almost unaffected. It was concluded that there is strong evidence supporting the hypothesis that ultrasonic GW propagation with HA-LFV effects can be analysed under the assumption of a permanently corrugated structure. •First research to understand HA-LFV effects on ultrasonic GW propagation.•Coherent noise appears in filtered ultrasonic GW signals affected by HA-LFV.•Coherent noise amplitude depends on LFV amplitude and on LFV-GW frequency ratio.•No coherent noise appears if SW and GW amplitudes have similar order of magnitude.•HA-LFV effects on GW seem equivalent to those of permanently corrugated shape.