Acoustic, Electron and Optical Microscopy Visualization of Surface and Sub-Surface Cracks
The purpose of the present study was to carefully document the early stages of fatigue damage in flush head riveted Alclad 2024-T3 aluminum alloy panel specimens. The fatigue cracks originate and initially propagate below the surfaces that are observable by optical and electron microscopy. Acoustic microscopy images such cracks and was employed to follow the observable sub-surface growth of fatigue cracks. In addition the cracks were monitored on the observable surface by optical and electron microscopy both in-situ and ex-situ during and after the test was completed. Careful fractographic analysis of the fracture surfaces was also done and correlated with the microscopic observations. The specimens used in this study were fabricated according to the specifications for the fuselage of an aircraft, and these specimens were not precracked or notched.