Diverse Applications of High Power Ultrasonics in Materials Engineering: From Manufacturing to Mechanical Testing (pp. 1-74)
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Authors: (M.R. Sriraman, Materials Science & Eng., The Ohio State University, USA)
Abstract: High power ultrasonics pertains to that realm of ultrasound carrying high vibratory
energy of intensities ranging from 104 to 1010 W/m2, which can cause permanent changes
to the material (unlike in ultrasonic non-destructive evaluation) to which it is imparted or
alter the nature of the process to which it is applied. Damping of energy due to internal
friction is said to be responsible for such phenomena.
In addition to some well-known processes that are currently used in engineering
industry, high power ultrasonics at ~20 kHz can also be applied to other processes such
as additive manufacturing, peening (through cavitation), and fatigue testing. Ultrasonic
additive manufacturing (UAM) is a layered manufacturing process (based on high-energy
ultrasonic welding) that is capable of fabricating intricate parts directly from a 3D CAD
drawing, using thin metal foils as ―building blocks‖. With no melting of materials
involved, the technology has a distinct advantage over other additive manufacturing
processes. In ultrasonic cavitation peening (UCP), the strong cavitation phenomenon
occurring in water from intense ultrasonic agitation is utilized in inducing residual
compressive stresses by work hardening of the metal surface exposed to it. Since the
process involves only water bubbles impinging on the surface, the technology is better
suited (than traditional shot peening) for small parts and hardening of selective/
inaccessible areas. Ultrasonic fatigue testing (UFT) involves testing the material to failure
by large cyclic strains internally generated through the imposition of high amplitude
ultrasonic vibrations under resonant conditions. While on the one hand the technology is
more meaningful to materials used in aerospace structures (and other components) that
are likely to experience intense high frequency vibrations during service, the speed of the
process (generating a million stress cycles in less than a minute) is also best exploited for
endurance/ fatigue limit investigations as well as in alloy development/ rapid screening of
materials.
