Investigation of the stress reduction and temperature increase due to ultrasonic vibrations with different amplitudes during compression tests of steels with varying specimen sizes.

High-frequency vibrations in the ultrasonic range influence the plasticity of metals during metal forming: there is stress and force reduction during ultrasonic treatment compared to metal forming without ultrasound. Different reasons for this behavior are discussed: a combination of stress superposition, energy absorption in dislocations, temperature increase, and frictional changes. This investigation shows the influence of partially superimposed ultrasonic vibrations with amplitudes in the range of ∼ 1.7to12 µm on the mean true stress reduction during compression test of the steels C15E and X6CrNiMoTi17-12-2 with diameters from 2 mm to 5 mm at a height/diameter ratio of one. Results show that the overall stress reduction is linearly proportional to acoustic energy or intensity for both investigated steels. The best-founded approximation of the size influence of the stress reduction is by the true diameter. In addition, an infrared camera and thermocouples were used to investigate and prove the temperature increase of the sample, which can occur at a magnitude of over 175 °C. The temperature increase due to the heating of ultrasound shows a sample size effect, too.