Early detection of fatigue damage through ultrasonic non-destructive evaluation - Part II: Experimental

Ultrasonic wave velocities (longitudinal and transverse waves) and the attenuation coefficient were used to investigate damage of aluminum 7075-T651 before and after progressive stages of fatigue. Repeated observations under controlled conditions allied to digital signal acquisition, autocorrelation, and regression were used to estimate small velocity and attenuation changes. Although comparatively small uncertainties were observed, the feasibility of utilizing the velocity of ultrasonic waves as a fatigue monitor was not substantiated under actual research conditions. However, careful measurements of the ultrasonic attenuation parameter demonstrated its potential to provide an early assessment of damage during fatigue. Part I of this work discussed the theoretical approach and described the fatigue testing procedures adopted in this investigation. This is a presentation and discussion of the experimental results.