Fatigue strength degradation by pitting damage

Naoe, Takashi   ; Futakawa, Masatoshi  ; Oi, Toshiyuki; Wakui, Takashi  ; Motohashi, Yoshinobu*

Mercury target will be installed at the material and life facility in J-PARC. Pressure waves will be generated in mercury by thermally shocked heat deposition when the high intense proton beams bombard the mercury target. Cavitation will be induced through the pressure wave propagation in the mercury and eroded the vessel inner surface contacting with the mercury. The eroded vessel wall is damaged by cyclic fatigue because pulsed proton beams strike the target repeatedly. It is, therefore, important to investigate the fatigue strength of the eroded vessel wall. In order to precisely investigate the effects of damages, at the first, the pitting damage by erosion was evaluated against the number of pulses, and then the fatigue test was carried out using the specimen with a certain pitting damage. As a result, the fitigue limit with pitting damage is degraded to less than half of that without pitting damage, after 2500 hrs operation at 1MW.