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Fastened joints are an integral part of aircraft design. Due to their complexity and function, they are also the primary source of structural fatigue problems. The incorporation of residual compressive stresses around a fastener hole greatly enhances the fatigue resistance and integrity of a fastened joint. This paper describes the split-sleeve cold expansion method to create residual compressive stresses which extend the fatigue life of holes in both new structure and field repairs. Data from test programs highlight process benefits and crack retardation effects for various specimen configurations. Other process features such as cold expansion to size are explained, along with the status of process automation.

Damaged or discrepant holes in metal and composites aircraft are time consuming and expensive to repair. Bushing the hole back to nominal size using press or shrink fit bushings; often in conjunction with doublers or local riveted patches, are not very effective and can change the local stiffness of the structure. Using a cold expanded high interference ForceMate repair bushing is a more cost effective alternative that has the advantage of not altering the local stiffness or dynamic response of the repair location while locally cold working the surrounding material to enhance the life and damage tolerance of the repair. A ForceMate2 panel repair method has been adapted to repair elongated or oversized holes in thin panel structures or removable access panels. This paper describes the methods and discusses testing and evaluation done to qualify the repairs in structural or panel repair applications.

This paper discusses an advanced design rivetless nut plate system which overcomes the inherent problems associated with typical riveted and rivetless nut plate configuration used in blind assembly of aerospace structures. The ForceTec™ (FtCx™) rivetless nut plate system presented utilizes hole cold expansion technology to radially expand a nut retainer into the fastener hole. Torque and push-out resistance are achieved by the resultant high interference fit of the retainer. Residual compressive stresses induced in the metal surrounding the hole during cold expansion and the reduction in applied cyclic stress range, caused by the high interference fitted retainer, significantly improve resistance to fatigue cracking. This system significantly reduces the high stress concentration associated with other methods and has demonstrated superior nut plate qualities with fast, consistent and reliable installation.