POSSIBLE MECHANISM FOR CAVITATIONAL EROSION.

Instability of the free surface of a viscous incompressible fluid in the field of a plane sound wave is considered as a model of cavitational breakdown. The problem is solved by Laplace-transforming in time and by series expansion with respect to a small viscosity coefficient. A second-order integrodifferential equation with periodic coefficients is thus obtained for the displacement of the free surface from its equilibrium position. Surface breakdown (instability) is shown to be characterized by a threshold. The existence of a threshold derives from the requirement that the sound energy transmitted to the metal must exceed the energy dissipated in the metal. In order to increase the resistance of metals to cavitational erosion, therefore, it is necessary to increase their dissipative capacity. Conclusions based on this model agree qualitatively with existing data on the cavitation resistance of metals.