Effect of laser peening on fatigue performance in 300M steel

Abstract

This study investigated and quantified the ability of laser peening to extend fatigue life and mitigate common fatigue crack nucleation mechanisms including foreign object damage and stress corrosion cracking in high strength, 300M steel. Residual stress was measured and fatigue tests were completed for as-machined, shot peened and laser peened coupons tested under a variety of conditions including in a corrosive environment and with simulated foreign object damage. The results are compared to available reference data studying the application of another emerging surface treatment, low plasticity burnishing, to the same material (300M steel) and in similar coupons. Laser peening resulted in large stress-life improvements in each condition, with a 54% increase in fatigue strength in an air environment for laser peened coupons at a lifetime of one million cycles. Additional fatigue testing in the 300M program showed that laser peening mitigated fatigue strength losses and improved the lifetimes (relative to as-machined, air environment) for coupons subject to either a corrosive environment or simulated FOD. Performance of laser peened coupons under all conditions proved to be better than reference data for coupons treated with shot peening or low plasticity burnishing.