Development of Laser Peening for Hidden Surfaces

In most gas turbine engines, the blades are held in rotating disks by a dovetail attachment that fits into a matching slot in the rim of the disk. The contact area between the blade dovetail and the dovetail slot is subjected to vibration and high stresses, leading to fretting conditions. Eventually, fretting fatigue cracks initiate in the fretting area and propagate into the disk and/or dovetail slot. Consequently, the disks are retired at a very conservative point in their service lives because of concerns about catastrophic fatigue failures. The application of a soft metallic coating to the blade dovetails helps to decrease this problem, but recoating and eventual retirement disks for fretting damage remains a significant problem and incurs a high cost. This program will build on a previous program to further develop the method to process inside hidden surfaces such as dovetail disk slots. Two issues will be addressed. The magnitude of the beneficial effect of laser peening with the laser system developed in this program to increase the fretting fatigue life associated with dovetail fretting will be evaluated. Also, the method for laser peening the inside fretting surfaces of dovetail slots will be matured. Lower equipment cost, ease-of-use reliability, and maintainability of hardware will be primary drivers.