Surface enhancement processes are extensively used to introduce compressive residual stresses (CRS) and enhance the fatigue performance in titanium and nickel alloy rotating components for Navy propulsion systems. CRS can relax in rotating components as a result of thermal exposure and cyclic stresses, adversely impacting the fatigue life and strength. Relaxation can occur rapidly depending upon the relative component temperatures and cyclic stresses. Inspection of the components is performed on a routine basis to characterize damage levels in accordance with Technical Manuals (TM). However, the CRS are currently not monitored and tracked during routine inspection. As part of the inspection cycle, components are re-shot peened to overcome any residual stress relaxation that may have occurred. Intervals at which the components are re-peened may or may not be appropriate for the rate of compressive relaxation. A portable XRD measurement device capable of quickly quantifying the CRS would allow the Navy to track the surface residual stress in support of condition based maintenance of critical components. The measurement device would allow for field measurement of critical features of blades and disk components. The device would be capable of not only measuring the surface residual stress but also the cold working which has a significant impact on the rate of relaxation.
Benefit: Successful completion of Phase I and II will provide a production-ready portable x-ray diffraction device capable of measuring the residual stress and cold working on critical rotating propulsion components. It is anticipated that the potential market for this measurement device in the maintenance and repair industry is significant. In addition to rotating component applications other fatigue critical components could be measured as well. All components taking advantage of compressive residual stresses to enhance fatigue properties could be monitored using the proposed measurement device. Furthermore, in most applications where high cycle fatigue or SCC is life limiting, the measurement and tracking of compressive residual stress by use of the portable device can save dramatic amounts of unnecessary reprocessing time.
Keywords: X-ray Diffraction, X-ray Diffraction, Condition Based Maintenance, Residual Stress, Nondestructive inspection, low cycle fatigue, tracking
