Limiting strain of metals subjected to high-intensity ultrasound

摘要

An experimental investigation of nonlinear acoustic internal losses in metallic materials used in the construction of high power ultrasonic transducers is reported. A method is proposed for the study of the attenuation at high strain level and for the determination of the limiting strain. The method is based on the measurement of the vibration velocity of a rod sample for different excitation levels keeping the temperature of the sample constant. The sample is driven at resonance by means of a piezoelectric transducer. The vibration velocities and temperatures are measured by a laser vibrometer and an infrared thermometer, respectively. Cylindrical stepped rod samples are used to achieve an increased strain amplitude in their central part. A simple linear model of the assembly constituted by the transducer and the sample is developed to relate the internal losses with the measured parameters. The results show the strain dependent behavior of attenuation under high-intensity ultrasonic stresses and determine the value of the limiting strain beyond which fatigue failure can be produced.