Method and apparatus for producing beneficial stresses around apertures, and improved fatigue life products made by the method

This invention is related to novel methods and tools for use in manufacturing parts with improved fatigue life, particularly for parts having fastener apertures therein, or cutouts therein, and which parts are subject to repeated or prolonged stress. More specifically, this invention relates to novel manufacturing techniques for providing improved fatigue life in parts, to utilizing the stress wave method for working parts, to improved tools for utilizing the stress wave method for working parts, and to finished parts made thereby, which parts have improved stress fatigue resistance characteristics. Metal coldworking tooling and a method of employing such tooling. The tooling is used to produce deformation in a workpiece, preferably via use of stress waves, to provide a selected beneficial residual stress profile in the workpiece, in order to provide high fatigue life structures in a minimum number of manufacturing steps. Preferably, action of an indenter causes propagation of stress waves to coldwork a workpiece, causing dimples in the workpiece. Preferably, the dimples are provided with a shape formed by application of a uniform pressure profile to the workpiece surface. By optimized use of the method, a relatively uniform beneficial residual stress profile is provided at both the surface and at the midplane apertures in a workpiece, so as to improve overall fatigue life. An improved indenter tool profile shape is described, having a smoothly curved indenter surface portion. Also, the use of a consumable lamina wafer technique provides the benefit of easy application of uniform stress profile to a workpiece.