Abstract :
Cold expansion is an e ective technique of inducing favorable compressive
residual stresses around fastener holes which are essentially vital for improving fatigue
performances of aircrafts. The bene t is derived through the magnitude and distribution
of the compressive stress eld. Stress gradients are entirely contingent on the type of the
cold expansion, local geometry of the hole, and characteristics of the metallic structure.
During cyclic loading, however, initial residual stresses do not remain stable. In the present
work, specimens with 4% split-sleeve cold expanded and reamed holes were cycled at the
fatigue limit for short periods. A recent method of Combined Step Drilling-Fourier Series
Solution ʹAT Ozdemir Methodʹ was employed to appraise the continual redistributions of
residual hoop stresses on the side of the hole subjected to cyclic load. Some results were
compared with those of di raction methods and Arti cial Neural Network (ANN) modeling,
where close similarities in stress distributions were con rmed. It is clear that the material
nearby the hole is dynamically hardening during early fatigue; in response, compressive
residual stresses along the bore are gradually increasing until the onset of cracking. Short
fatigue cracks are mostly initiated from the mandrel entrance side, where, subsequently,
residual hoop stresses begin to relax considerably.
