Adaptive Mode Filter for Lamb Wavefield in the Wavenumber-Time Domain Based on Wavenumber Response Function

Abstract

Aerospace thin-walled structures are susceptible to various forms of damage and they can be effectively inspected using Lamb wavefields. However, Lamb wavefields contain at least two dispersive modes which interfere with the generation of a clear image for damage visualization. Conventional mode filters produce inconsistent results due to the need for the ad hoc or manual adjustment of the processing parameters by experienced users. An automatic, adaptive mode filter is proposed to remove human subjectivity, thereby improving the consistency of the results and making it more practical to utilize. It converts the wavefield from the space-time domain to the wavenumber-time domain and then consolidates the data in the time and angular axes into a wavenumber response function (WRF) where the modes can be automatically isolated. The single-mode data were converted back into space-time domain for result visualization. Its effectiveness was experimentally proven by keeping 78.2-122.0% of energy for a wanted mode and suppressing the energy of an unwanted mode to 0.1-4.5%. Its automatic adaptability was demonstrated through the improved visibility of a blind hole, corrosion, water-ingress in honeycomb panel, and impact damage in a complex composite wing. Consistent results can be generated in a highly efficient manner while significantly reducing the computational workload and hardware requirements.