EFFECTS of Laser Peening ON Fatigue LIFE IN AN Arrestment Hook Shank Application for Naval Aircraft

Laser peening is evaluated relative to and in combination with other means of improving fatigue resistance in a particularly severe arrestment hook shank application for a carrier-based Naval aircraft.  A large-scale test specimen was designed and manufactured from Hy-Tuf steel to geometrically simulate conditions in the arrestment hook shank, and fatigue tests were conducted on peened specimens under conditions of spectrum loading that simulate aircraft arrestments.  Laser peening substantially increases the resistance to crack initiation relative to conventional shot peening.  A change to a higher-strength steel, Ferrium S53, significantly increases the crack initiation life of both conventionally shot peened and laser peened specimens, with the latter exhibiting the highest levels of crack initiation life for all conditions evaluated in this test program.  Proof loading at levels above the design limit load, conducted before the peening operation, substantially increases the crack initiation life of conventionally shot peened specimens.  In contrast, proof loading does not provide additional improvements in the fatigue life of laser peened specimens since the depth of plasticity due to proof loading is similar in magnitude to the depth or residual compressive stress introduced by laser peening.  Finally, limited test results suggest that repeated laser peening over the life of a component may maximize or even extend crack initiation life; however, a significant amount of testing would be required to determine the processing parameters that maximize the efficacy of this approach to extending fatigue life.