A system to study the influence of ultrasound on mechanical behavior



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A system was assembled to study the effects of high- power ultrasonic vibrations on the mechanical properties of materials. A special holder was fabricated to allow for the simultaneous application of the static and the dynamic stresses. Also, the specimen used in the test was specially designed for the study of high ductility materials and for use at variable temperature environment. The displacement amplitude of the ultrasonic vibrations was measured by means of a fotonic sensor in order to calibrate the dynamic stress imposed on the specimen during the tensile test. This amplitude was also calculated using a wave equation for propagation in a continuous media and assuming noninteraction between the dynamic and the static stresses. The agreement between measured and calculated amplitude made it possible to evaluate the ultrasonic stresses in the specimen at positions where measurements were not possible. The stress-strain behavior of Aluminum 6061-T6 was examined while the ultrasonic vibrations were applied continuously and interruptedly. From these tests, it was found that both the flow stress and the strain to fracture were decreased due to the application of the ultrasound. The decrease in the flow stress was interpreted in terms of dislocations breakaway from pinning points when the ultrasound was applied. The decrease in the ductility, however, was believed to be due to the multiplication of the dislocations in the specimen.