SURFACE-LAYER ACTIVATION FOR MEASURING FRETTING WEAR

Oscillations that cause fretting typically have sufficiently small amplitude to insure continuous contact so that debris cannot escape. The presence of debris aggravates the process and can lead to fatigue cracking. Surface layer activation (SLA), which utilizes radionuclide surface markers, is developed to measure wear associated with fretting. Gamma rays from the marker are measured by an externally mounted scintillation detector. Decreases in gamma ray signal due to debris removal (after correction for natural decay half-life) result in a direct on-line measure of wear. Test results are reported for titanium alloys, but the technique is equally applicable to detecting surface damage in other materials. SLA is most useful for wear characterization of parts which are inaccessible or in hazardous environments. For fretting evaluation, gamma analysis was used on components of the dismantled system both to measure loss from the activated part and to detect material transferred to the mating surface and in the collected debris. On-line monitoring of fretting wear is possible if debris is reliably removed from the wear site.