Abstract
When negative pressure occures at some part of water flow, water is separated. and cavities are formed there, because water cannot resist tensile stress. Wherever the absolute pressure falls to (or close to) the vapor pressure of water, cavities are also formed. They will be carried along with water flow and collapse at the place of high pressure. This phenomenon is called cavitation.
The magnitude of the pressure created by the cavity collapse is enough to erode and destroy the surface of a hydraulic structure. The accumulative erosion and destruction may endanger the hydraulic structure. Although the damaging or “pitting” of structural materials by cavitation has been variously attributed to chemical action, electrochemical action (corrosion), high tension in water, etc., present evidence indicates conclusively that the destructive action is essentially a mechanical one, being caused by the impact of water mass on the surface of the material.
This paper describes what material is applicable to cavitation experiment, and how is the process from occurrence to erosion and destruction. This experiment has been done with various conditions and shapes of the solid surface.
It is found from the result of the experiment that, in order to prepare the most adequate test-piece (made of “plaster of Paris”) for surface erosion experiment of cavition, the water content must be five to six times as much as that of the standard mix ratio and the stirring time must be two times as long as that of standard mixture. By using this material, it becomes comparatively easy to obtain the erosion of cavitation on the test-piece surface within a short test period.
