A health management technology for multisite cracks in an in-service aircraft fuselage based on multi-time-frame laser ultrasonic energy mapping and serially connected PZTs

Abstract

The problems of multisite fatigue crack growth and multiple interacting cracks in aircraft fuselage structures may incur catastrophic failure. This article proposes a structural health management (SHM) strategy for multisite cracks in the skin and the vicinity of fastener holes in lap joints and demonstrates that the strategy is effective in an in-service metallic aircraft fuselage. To this end, the present article uses a conductive fabric tape-equipped serially connected piezoelectric sensor array combined with an ultrasonic propagation imaging (UPI) system. The serially connected piezoelectric sensor array is defined as a single sensor that has multiple sensor nodes with one electrical output. It was connected with conductive fabric tape instead of lead wire due to its comparatively low attenuation, light weight, and compact and easy installation on the internal structures of the complex fuselage. This technology does not require multi-cabling and multi-channeling because of its ultrasonic propagation imaging capability from multiple sources of the UPI system. The fuselage side skin of a Cessna-150 with various crack locations and orientations was tested using the proposed SHM technology. The ultrasonic wave propagation imaging video showed multisource wave propagation, and all of the crack-induced scattering wavefields appeared at different times because of the large inspection area. Therefore, we have developed a multi-time-frame ultrasonic energy mapping algorithm, which was processed in the wavenumber domain to visualize the cracks. Consequently, the lightweight, easy, and compact installation of the serially connected PZTs and their combination with the UPI system were shown, demonstrating that the SHM strategy for multisite cracks in an in-service aircraft fuselage is effective.