Abstract
The effects of strain range on the ultrasound fatigue lifetime in brass and aluminum was investigated. The tests were performed on resonant dumbbell specimens predicted to fail over a range of 10,000 and a billion cycles, using a piezoelectrically driven exponential horn vibrations at 20 KHz and a displacement amplitude ranging between 10 to the -4th and -6th meters. The specimens consisted of a gauge length with an arc of circular profile, flanked by a constant cross-sectional area shoulder. The stress distribution along the gauge length was calculated using a hyperbolic cosine function to represent the arc of the circle. Tensile tests were also conducted to examine the effects of strain hardening on crack growth. The number of cycles to failure reasonably agreed with Manson's fatigue life predictions in the elastic strain range, and indicated that failure in ultrasound fatigue is mainly due to stage II crack growth.