Modeling capability for realizing engineered residual stress due to mechanical surface treatment Navy SBIR FY2005.1 Sol No.: Navy SBIR FY2005.1 Topic No.: N05-026 Topic Title: Modeling capability for realizing engineered residual stress due to mechanical surface treatment Proposal No.: N051-026-1099 Firm: Hill Engineering, LLC 822 Linden Lane Davis, California 95616-1713 Contact: Michael Hill Phone: (530) 304-7296 Abstract: Laser Peening (LP) and Low Plasticity Burnishing (LPB) are two recently emerging surface treatment technologies capable of introducing deep, near-surface residual stress. While judicious use of these treatments is often of significant benefit to structural component fatigue lives, no prediction model currently exists to help reduce the significant empirical burden generally associated with their implementation. This proposal outlines a methodology for developing a computational design tool for the implementation of LP and LPB. The introduction of residual stress is based on eigenstrain, embodied in a finite element context. Through superposition, the residual stress field and the reactionary stress field due to applied loading can be combined, offering valuable insight into the resultant stress field. Most importantly, the resultant stress field can be evaluated for detrimental tensile stress regions sometimes generated inadvertently in these deep surface treatments. Although the methodology is of a general nature, turbine engine blades are selected for a component-specific design in this study proposal. LP is applied to the leading edge of these blades to suppress crack growth due to Foreign Object Damage (FOD). The effect of LP on FOD-nucleated crack growth and the fatigue life of compensatory tensile stress regions are to be assessed and verified. Benefits: Due to their ability to significantly alter stress fields within a body, misapplication of LP and LPB can sometimes degrade component fatigue lifetimes through compensatory tensile regions. Carefully implemented empirical approaches are needed, therefore, to effectively introduce these treatments. Even so, there can be a disconnect between successful laboratory treatments and successful in-field component results, where slight changes in geometry, loading, and surface treatment application can interact to wreak havoc. A design tool for analysis prior to actual component treatment could eliminate much of the costly empirical burden imposed by such difficulties. Fatigue problems are found throughout industry. Surface treatments like LP and LPB have the potential to beneficially affect a significant number of these fatigue problems. A design tool as proposed is expected to significantly reduce the financial and time costs associated with applying LP or LPB treatments in every one of these design problems. Return