Influence of ultrasound on the strain hardening behaviour of metallic materials
Final Report Abstract
The introduction of ultrasonic vibrations (UV) into manufacturing processes such as cutting, forming and joining is used to reduce process forces and thus save energy and resources. The first known investigations into the materials science basis of this force reduction through ultrasonic vibrations in the plastic flow of metals were first described in 1955 by Blaha and Langenecker. They observed that the superposition of an ultrasonic vibration during plastic flow in the quasi-static tensile test leads to a reduction in the yield stress and to a change in the hardening behaviour during UV compared to a curve without UV. These effects and the factors influencing them are not yet fully understood; mechanical stress superposition, absorption of UV energy in dislocations, temperature input and friction reduction are being discussed. In the project, a ferritic-pearlitic steel (C15E) and an austenitic stainless steel (X6CrNiMoTi12-12-2) were used to evaluate the effects of UV on different lattice structures and thus different deformation behaviour. Reversible and irreversible effects on the deformation behaviour were observed by varying the UV amplitude and UV duration: The mean stress reduction of the flow stress due to UV (acoustic softening) is quadratically proportional to the UV-amplitude for both materials analysed. A volume influence is observed, which mainly depends on the diameter of the samples. The strain hardening and thus the dislocation density when the UV is applied show no significant influence on the acoustic temporary softening. The materials show an increase in temperature during UV, which is dependent on the UV amplitude. Ring crush tests indicate an increase in friction during UV. The UV-induced temperature rise and the increase in friction influence each other. The ferritic-pearlitic steel shows a reversible softening behaviour after UV for all tested UV amplitudes. The austenitic stainless steel tends to undergo irreversible softening over longer UV durations depending on the amplitude. The hardening behaviour of austenitic steel in particular changes during UV. The microstructural results indicate a concentrated plastic deformation in the centre of the sample. This is also confirmed by the grain size analysis and hardness measurements. In contrast, the end faces of the samples show a decrease in hardness and thus also a low degree of deformation under UV.
Publications
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Einfluss von Ultraschall im Zylinderstauchversuch. In: Werkstoffe und Bauteile auf dem Prüfstand, Tagungsband Werkstoffprüfung 2019, Herausgeber: H.-J. Christ, S. 373 - 378, 2019, ISBN 978-3-88355-418-1
M. Burmeister & E. Kerscher
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Investigation of the stress reduction and temperature increase due to ultrasonic vibrations with different amplitudes during compression tests of steels with varying specimen sizes. Ultrasonics, 134, 107053.
Burmeister, Markus & Kerscher, Eberhard
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Ultrasonic Vibration Influences on the Flow Stress Behavior of a Ferrite-Perlite and Austenite Stainless Steel. Lecture Notes in Mechanical Engineering, 751-758. Springer Nature Switzerland.
Burmeister, Markus & Kerscher, Eberhard
