Monitoring Fatigue Cracks in Riveted Aerospace Plates Using Nonlinear Ultrasonic Techniques

Abstract

Aluminum structures are commonly used in aircraft due to their lightweight and corrosion resistance compared to other metals. Often multi-layered aluminum plates are joined by rivets which are prone to fatigue crack formation in aircrafts. Therefore, the detection and monitoring of fatigue cracks at rivet joints in aluminum structures are crucial for ensuring flight safety. In this study, piezoelectric sensors are used to generate and detect Lamb waves on aluminum plates with rivet joints. The feasibility of a newly developed nonlinear ultrasonic technique called Sideband Peak Count (SPC) technique is investigated for detecting fatigue cracks near these joints. To overcome some limitations of existing SPC-I and SPI ((a modified version of SPC-I) techniques in capturing harmonic and modulating wave frequencies due to material nonlinearity, another index called the Sideband Intensity Index (SII) is introduced. Comparative analysis of SII with existing SPC-I and SPI techniques show some advantages of the SII technique. Research findings demonstrate that the SII technique can reliably detect fatigue cracks around rivet joints on aluminum plates. This study offers a more efficient method for detecting critical fatigue cracks in rivet joints.