Application of a fracture mechanics based life prediction method for contact fatigue

Fretting fatigue, or contact fatigue, is defined as damage resulting from small magnitude (0.5–50 microns) displacement between contacting bodies where at least one of the bodies has an applied bulk stress. Of particular importance at the present time is the occurrence of contact fatigue in the blade to disk attachments in aero-engines. Appraisal of the various fretting fatigue life prediction methods currently available suggests that those based on computation of “stress at a point” or a function of stress at a point are not always sufficiently accurate. Further, stresses averaged over a critical volume have problems associated with that approach. Thus, the applicability and limits of a fracture mechanics-based life prediction methodology are explored in the present paper. Results from this modeling approach are compared to experimentally determined fretting fatigue life on various contact geometries, including sphere/flat, cylinder/flat, flat-on-flat and the more realistic dovetail configuration relating to blade-disk attachments.