Correlating Inertial Acoustic Cavitation Emissions with Material Erosion Resistance

Abstract

The standard ASTM G32-10 concerns the hydrodynamic cavitation erosion resistance of materials by subjecting them to acoustic cavitation generated by a sonotrode. The work reported extends this technique by detecting and monitoring the ultrasonic cavitation, considered responsible for the erosion process, specifically for coupons of aluminium-bronze alloy. The study uses a 65mm diameter variant of NPL's cavitation sensor, which detects broadband acoustic emissions, and logs acoustic signals generated in the MHz frequency range, using NPL's Cavimeter. Cavitation readings were made throughout the exposure duration, which was carried out at discrete intervals (900 to 3600 s), allowing periodic mass measurements to be made to assess erosion loss under a strict protocol.Cavitation measurements and erosion were compared for different separations of the sonotrode tip from the material under test. The maximum variation associated with measurement of cavitation level was between 2.2% and 3.3% when the separation (λ) between the transducer horn and the specimen increased from 0.5 to 1.0mm, for a transducer (sonotrode) displacement amplitude of 43.5μm. Experiments conducted at the same transducer displacement amplitude show that the mass loss of the specimen —a measure of erosion— was 67.0mg (λ = 0.5mm) and 66.0mg (λ = 1.0mm).