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Early attempts to produce cavitation erosion on a stationary specimen close to a vibrating probe showed promise as a means of testing weak materials and coatings. However, the geometry affected the damage rate, the condition of the cavitating liquid was not accurately known, and the temperature in the cavitation zone rose appreciably. An improved version of this test has been devised at the University of Strathclyde, Glasgow, and subsequently further developed at the National Engineering Laboratory, East Kilbride.
The specimen is mounted a small distance from the vibrating probe, and liquid is fed continuously through a central hole in the stationary specimen. With water the temperature rise could be kept easily below 2 C. In oil, although the temperature rise was considerably higher (10 C) it was under complete control and depended mainly on the flow rate and specimen separation.
The erosion pattern obtained on the stationary specimen was well distributed and fairly uniform. The rate of erosion reach an early maximum value and then decreased with time. It decreased as the separation was increased. Optimum test conditions were obtained with 0.5 mm (0.020 in.) separation from a 20 kHz vibrator having a peak-to-peak amplitude of 50μm (0.002 in.). The specimen and vibrating probe were both 16 mm (5/8 in.) diameter. Effects of probe amplitude, test liquid flow rate, temperature, and static pressure were examined.
This technique has been used with considerable success for the evaluation of white-metal layers in lubricating oils, fiber-reinforced epoxy resins in water, and a range of typical engineering alloys.
cavitation, erosion, liquids, metals, physical properties, testing, vibration, wear, evaluation, tests
Principal scientific officer, Fluids Group, National Engineering Laboratory, Glasgow,
Senior lecturer, University of Strathclyde, Glasgow,