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.