Method and Apparatus for Manufacturing Structures with Improved Fatigue Life

Author:  Eric T. Easterbrook and Nils Juhlin
Source:  US Patent 6,742,376
Doc ID:  2004059
Year of Publication:  2004
Abstract:  
A compound indenter for metal coldwork, and a method of employing such tooling. The compound indenter tool is used to produce deformation in a workpiece structure, 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 a compound indenter causes deformation of the workpiece, causing dimples in the workpiece. 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, compound indenter tool profile shape is described, having a first, elongate indenter with a shaped indenter surface portion, and a second shaped indenter surrounding the first indenter and forming an annular shoulder recessed from the surface portion of the first indenter. Additionally, a foot having a bottom portion can be used to confiningly surround the second indenter during application of force to the surface of a workpiece, to prevent surface deformation.