Relation between impact load and the damage produced by cavitation bubble collapse

Abstract

In order to study the relation between impact load by collapsing cavitation bubbles and erosion damage, a new pressure detector which can measure impact loads and erosion damage (size of indents or pits and volume loss) simultaneously was developed. The detector consisting of a test specimen with a diameter of 3 mm and a piezoelectric ceramic disk was used for venturi tests and vibratory tests. Impact loads by collapsing bubbles were observed directly in a venturi tunnel and as piled-up pulses on an alternate wave of hydrodynamic pressure produced by a vibrating disk in a vibratory device. Peaks of waves were held and measured before arrival of the reset pulses with an interval of 100 μ. The distribution of impact loads was computed after A/D conversion of the peak hold waves. Impact load occurring in an early stage in the venturi facility and vibratory device were compared with indent size which were observed with a microscope on the surfaces of pure aluminum, pure copper and austenitic stainless steel (SUS304). A linear relation was obtained between impact load and the area of indents in both the venturi and vibratory tests. There exists a linear relation between the dynamic hardness under impact loads due to cavitation bubble collapse and critical impact loads for fcc metals, but bcc metals deviate from this relation. The plastic energy required to form a pit of aluminum and copper under impact load is about one order larger than that under static load. The energy based on impact loads was compared with the volume loss of the specimen. It is concluded that a linear relation was obtained between the accumulated impact energy and the volume loss irrespective of test conditions such as type of apparatus, flow velocity for venturi test and the distance between a vibrating disk and specimen for vibratory test.