Nondestructive positron-lifetime measurements during fatigue of austeniticstainless steel using a mobile positron beam

Nondestructive positron-lifetime measurements have been performed during st ress-controlled symmetric fatigue of austenitic stainless steel up to failu re for different applied stress amplitudes between 230 and 300 MPa. For thi s purpose a fatigue machine has been equipped with a mobile positron beam e mitted from a 22 mu Ci (0.8 MBq) Se-72/As-72 generator. A pronounced increa se of the mean positron lifetime has been found within the first 10% of fat igue life. Saturation has been reached after 40% of fatigue life. The mean positron lifetime at failure depends strongly on the applied stress amplitu de. (C) 2000 American Institute of Physics. [S0003-6951(00)02838-2].