Split Sleeve Coldworking

Split Sleeve Cold Working stops the occurrence of fatigue cracks around fastener holes in metal structures. The system consists of pulling a tapered mandrel lined with a lubricated split sleeve through a hole in metal. The split sleeve ensures correct radial expansion whilst protecting the hole. The plastic flow of material caused by drawing the mandrel through the start hole creates an annular zone of residual compressive stresses which reaches approximately one diameter from the edge of the hole. The magnitude of this compressive stress is approximately equal to or more than 2/3 of the yield strength of the material.

The zone of residual compressive stresses decreases the effect of the tensile stresses caused by cyclical loading and has proven to prolong fatigue life by at least 3 times. A one sided operation which adds no weight to the metal structure, Split Sleeve Cold Working is an excellent method of prolonging fatigue life in fastener holes.

Cycles to failure

Split Sleeve Cold Expansion

Under cyclical loading conditions fatigue cracks may occur around fastener holes causing fatigue cracks and subsequent failure of the structural component. In order to solve this problem the Split Sleeve Cold Expansion system was developed by the engineers at the Boeing Company in the late 1960's. Most airframe manufacturers, both comercial and military have since then incorporated the system into their designs. But there are also other applications such as space, railroad and energy.

The method consists of pulling an oversized tapered mandrel through a hole in metal which is fitted with an internally pre-lubricated split sleeve.

The disposable split sleeve prevents seizure and minimizes surface upset of the material at the same time as it ensures correct radial expansion whilst protecting the hole. The required final hole diameter is obtained by post reaming the hole thereby eliminating the axial ridge left by the split in the sleeve.

The plastic flow of material caused by drawing the oversized mandrel back through the hole with the Split Sleeve creates an annular zone of residual compressive stresses which reaches approximately one diameter from the edge of the hole. A balancing zone of tensile stresses lies beyond the residual compressive stress zone.

Considerations

Disposable split sleeve

Axial Ridge

Compressive stresses

The zone of residual compressive stresses form a barrier and stops the tensile stresses caused by cyclical loading from reaching the hole where they could propagate a scratch or crack. As a result the risk of crack growth and fatigue failure decreases significantly improving fatigue life of by approximately 3:1.

A one sided operation which adds no weight to the metal structure, Split Sleeve Cold Expansion is a cost efficient method of improving fatigue life in fastener holes used both in production and repair. Although primarily used in the aviation industry, turbine engines, railroad track and other metal structures also have applications.