a method for cold working metal structures . a compound indenter is used to produce deformation in a workpiece , to provide a selected beneficial residual stress profile , to provide improved fatigue life structures with minimal manufacturing steps . a compound indenter deforms a workpiece , resulting in dimples therein . a relatively uniform beneficial residual stress profile is provided at the surface and at the midplane of apertures in a workpiece , so as to improve overall fatigue life . a compound indenter tool 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 , is used . optionally , a foot having a bottom portion is used to confiningly surround an indenter during application of deforming force to the surface of a workpiece , to prevent deformation of adjacent workpiece surface .