Investigating the effect of cold expansion on frictional force evolution during fretting fatigue tests of AL2024-T3 plates

In this paper, fretting fatigue experiments are conducted on cold expanded holed plates using fretting test configuration which is designed to simulate fretting fatigue condition around the holes. Two values of normal contact force and longitudinal cyclic load are applied on the specimens, and the evolution of friction force is measured during the tests. Finite element simulation is performed for better understanding of the cold expansion process and its effect on the contact configuration. The obtained results show that a high degree of cold expansion does not increase fretting fatigue life. Moreover, the value of frictional force is low at the early cycles of tests and increases to reach a stabilized value. The stabilized value of frictional force on the entrance and exit planes of low degree cold expanded specimens is almost the same, while it is lower on the exit plane of high degree cold expanded specimens in comparison to the entrance plane of the same specimen. It is revealed that the geometrical change that occurs on the plate during the high degree cold expansion process is the main cause of this phenomenon, while the increased hardness around the hole is the subsidiary factor.