11 



An example of damage to a marine propeller subjected to cavitation 

 for a few days of service is shown in Figure 10. In this case there is actu- 

 ally erosion of the metal. Figure 11 shows cavitation on several concrete 

 specimens tested by the Bureau of Reclamation. The form of the damage will, 

 however, depend upon the material; lead, for example, exhibits deformations of 

 the surface without appreciable loss of material. This point will be dis- 

 cussed further in connection with the mechanism of damage. 



SOME IDEAS ON THE INCEPTION OF CAVITATION 



PRELIMINARY REMARKS 



As mentioned in the foregoing, for most engineering applications, in- 

 ception of cavitation may be expected when the local pressure drops to the 

 vapor pressure corresponding to the temperature of the liquid. However, this 

 is only an approximation which, while useful for design purposes, requires 

 careful qualification. Depending upon the condition of the liquid (air or 

 solid matter content, etc.), cavitation may begin above or below the vapor 

 pressure. It is well known that clean, degassed liquids can withstand large 

 tensions or may be superheated considerably without formation of cavities or 

 inception of boiling. It is now gen- 

 erally accepted that the inception of 

 cavitation in a flowing liquid or 

 boiling in a heated liquid originates 

 with the formation of gas or vapor 

 nuclei. Consequently, it is of inter- 

 est to examine the kinetics of forma- 

 tion of such nuclei in connection 

 with cavitation resulting from pres- 

 sure reduction. For discussions of 

 inception of boiling in heated liquids, 

 reference may be made to References 21 

 and 22 , for example . 



TENSILE STRENGTH OF LIQUIDS - RESULTS 

 OF RECENT ATTEMPTS TO FORMULATE A 

 KINETIC THEORY OF CONDENSED SYSTEMS 



Since the concepts which are 

 of interest to the present discussion 

 are an outgrowth of attempts to deter- 

 mine the tensile strength of liquids 



Figure 10 - Cavitation Damage 

 on a Marine Propeller 



