D. Sokol, A. Clauer, D. Lahrman, LSP Technologies Incorporated, Dublin, OH; D. See, USAF Air Force Research Lab, Wright Patterson AFB, OH; L. Bernadel, Navair, Patuxent River, MD
Laser peening has been a commercial surface enhancement process for over six years, and the number of applications has been gradually expanding. A new use for laser peening involves increasing the fretting fatigue resistance of Ti-6Al-4V and other titanium alloys. Fretting fatigue is a problem associated with many mechanical systems where there is metal-to-metal contact under vibrating load conditions. This is a particular concern in some aircraft engine components such as the contact surfaces between the dovetail attachments of the engine airfoils or blades and the disk slots in which they are seated in the rotating disks. Laser peening has the potential to enhance the resistance of these components to failure by fretting fatigue.
Fretting fatigue tests were performed at Purdue University to evaluate the effect of laser peening with large (greater than 5 mm diameter) and small spots (1 mm diameter and smaller) on fretting fatigue. In the tests, laser peened fretting fatigue bars fabricated from Ti-6Al-4V forged plate were subjected to fretting fatigue conditions consisting of fretting concurrent with fatigue cycling. The specimen design simulated the fretting contact occurring between the blades and dovetail slots during operation of an aircraft engine. The results showed that laser peening with either large or small spots dramatically increased the fretting fatigue life under applicable loading conditions by at least 25 times.
Small spot laser peening enables the processing of the inside of small, generally inaccessible areas such as the insides of holes and dovetail disk slots. A review of the of the process equipment and fatigue results will be presented.
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