Laser Peening for Army Vehicle Life Extension

Laser peening significantly increases the fatigue life of components by the introduction of deep compressive residual stresses. The U.S. Army utilizes numerous fatigue-critical components, which potentially could take advantage of the improvements offeredby laser peening. Such parts include gears, which are used in a variety of aircraft, vehicles, and support equipment. Helicopter gears are of particular interest because these gears are prone to fatigue failures, which lead to high inspection andmaintenance costs.Limited attempts to match the demonstrated fatigue life benefits achieved with laser peening for titanium-alloy engine parts in hardened steel gears have fallen short of expectations. This result is believed to be related to the presence of a hardenedsurface layer and the rather complex gear geometry. A program is proposed to characterize the interaction of the shock wave with the microstructural features and gear tooth geometry. This information is needed to develop improved laser peening methodsfor fatigue-resistant, steel gears.The need within the military and private sectors for increased gear life is important and urgent. The development of affordable laser peening processing for gears will have a tremendous economic impact through enabling more reliable, fuel efficientvehicles along with reduced maintenance, repair and gear replacement costs. The benefit of this program will be to provide a laser peen processing method that increases the fatigue life of gear components for the Army. The new processing methods can beapplied to all components beyond the Army needs. These applications include, for example, the lift fan gears that are to be used in the Joint Strike Fighter for the Navy/Marines. Other low cost parts, such as gears and shafts for automotive applications,will be able to take advantage of the LaserPeenT process developed in this program.