Necessary conditions for cavitation

While the surface modification is not effective to suppress cavitation, Yee and coworkers performed an experiment to suppress the cavitation mechanically in a rubber-modified epoxy network. They applied hydrostatic pressure during mechanical testing of rubber toughened epoxies [160]. At pressures above BOSS MPa the rubber particles are unable to cavitate and consequently no massive shear yielding is observed, resulting in poor mechanical properties just like with the unmodified matrix. These experiments proved that cavitation is a necessary condition for effective toughening. 

According to studies reported in Ref. 738, a multimolecular layer of the product is formed on the metal surface. Since for its formation the presence of metal atoms or ions on the border between liquid and solid phases is needed, a diffusion of metal atoms through the compound layer is a necessary condition for such layer formation. The cavitation processes on the surface contribute to this. Since an energetic barrier should be mastered in the reaction route, a cavitation ultrasonic action has the same importance as triboplasma formed by metal friction [756]. 

As discussed in the previous section, cavitation of rubber particles is practically necessary for toughening. In this section, some conditions important for cavitation to occur will be discussed. 

For the quantitative relationship of the effects, the work of Gogate and Pandit (2000a) is recommended. They have given a correlation for the estimation of collapse pressure as a function of different operating conditions, which clearly gives a quantitative idea about the optimum parameters. It is necessary that both the frequency and intensity of irradiation should not be increased beyond an optimum value, which is also a function of the type of application and the equipment under consideration. The liquid-phase physicochemical properties should be adjusted in such a way that generation of cavitation events is eased and also large number of smaller-size cavities are formed in the system. 

The limits of the cavitation area are marked by the points of angular locations a and P where (16) goes through zero. In the usual theory, this represents the Gumbel s condition. As it is already noted in Tichy and Bou-Said s paper [15], for inertia case, P does not necessary equal a + n. 

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