Acoustic Characteristics of Fatigued Aluminum Alloy Using Ultrasonic Shear Waves

Cyclic-tension fatigue of aluminum alloy, Al-4Cu-1Mg, was determined by an analysis of diffracted SH and SV waves, passing through the surface and reflecting the bottom of the specimen, respectively. The internal friction of SV waves begins to increase from fatigue damage ratio(=N/Nf) of 0.5. This suggests increase of movable dislocation. From the analysis of SH waves, the logarithmic damping ratio and the propagation time decreases with increasing of the degree of fatigue. Assumed from SH wave flux model, the residual stress field applied by cyclic-tension makes the damping ratio and the propagation time decrease. The experimental result correlates well with this theory. These results show that ultrasonic method is useful probe for evaluation of fatigue in aluminum alloy. KEYWORDS; fatigue, aluminum alloy, cyclic tension, nondestructive inspection, acoustic characteristic