The purpose of this paper is to discuss several metal treatment approaches, based on deep residual stress (DRS) treatments, that can transform mechanical system members with little or no damage tolerance into members capable of satisfying the damage tolerance requirements of FAR 29.571. These approaches include: (1) Cold-working with an oversized mandrel, (2) ForceMate® cold-expanded bushings, and (3) Laser shock peening. The differences between the DRS approaches and the relative advantages of each are discussed, as are the challenges which must be overcome in successfully implementing each approach. The need for a holistic approach which combines simulations of the manufacturing treatment processes used to induce the residual stresses with the traditional DTA analyses is emphasized, due to the large plastic strains induced and the risk of premature failure during the application of the DRS treatment. Engineering models for predicting the strains during the cold-working or laser shock peening treatment process and the resulting residual stresses are discussed, along with a weight function-based approach for determining the stress intensity factors for a crack growth analysis. Examples are presented comparing the crack growth lives of typical mechanical system members with and without the DRS fatigue life enhancement treatment to illustrate the relative advantage of each method, and to illustrate the potential of these methods in imparting damage tolerance to mechanical and dynamic system components.
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