PRELOADING TECHNIQUE IN DYNAMIC FATIGUE TESTING OF CLASS AND CERAMICSWITH AN INDENTATION FLAW SYSTEM

The solution of fatigue strength as a function of preloading in dynami c fatigue testing was obtained numerically for an indentation flaw sys tem. The dynamic fatigue strength is dependent on preloading and fatig ue parameter (n). The effect of preloading on dynamic fatigue strength decreases with increasing fatigue parameter: for n greater than or eq ual to 20 the effect is negligible up to a preloading of 90%. The solu tion was verified by dynamic fatigue experiments conducted with soda-l ime glass and alumina specimens with as-indented flaws in room-tempera ture distilled water. The result indicates that one can apply a preloa ding corresponding up to 90% of fatigue strength for most glass and ce ramic materials with no change in fatigue strength, resulting in a dra matic saving of testing time.