Cold-working is one of the important techniques for improvement of material quality and strengthening. The effect of cold-working on fatigue life of notched specimen in carbon steel was investigated. The purpose of present study is to propose a new technical method for enhancement of fatigue life in a notched specimen, Also, effect of local plastic deformation by cold work on fatigue crack growth behavior was examined. This paper presents a new experimental kinematic cold expansion method based on insert and remove, and insert circular and elliptical pin through the specimen hole. Cold-working is a simplex process where mechanical and thermal fatigue combines with impact, abrasion, adhesion and corrosion, which all depend on system interactions rather than material characteristics only. It was shown that the fatigue life of the specimen with the cold-worked hole was longer than that of the specimen with non-cold-worked hole for the case of same stress level in a 0.45% Carbon Steel. Also, the fatigue strength was higher in the case of the cold expansion hole. The reason for the prolonged life of the steel with cold-worked hole is related to retarding the initiation life of fatigue cracks. In this study, a methodology of lengthening of fatigue life of holed specimen is shown. In this paper a series of fatigue life measurements and fatigue crack growth tests have been carried out using 0.45% Carbon Steel specimens containing cold expanded and non cold expanded holes. As well as fatigue crack initiation life, fatigue crack growth rates in specimens containing cold expanded holes were improved. Also, the improvement conditions were significantly affected by the shape of pin. Three different batches of specimen were produced for fatigue testing. The first samples had the non-cold-worked holes center in the drilled state, the second and third batches had their drilled holes cold expanded by insert and remove circular and elliptical pin directly force an oversized pin through the hole. In addition, the third batch with cold expanded holes was then subjected to insert but not removed. The fatigue life improvement of the damaged structures has been studied. Since, such damage can be origin of fatigue crack initiation; the removing the damaged section by drilling hole and applying cold expansion are considered to be effective method for improvement of damaged components in some cases.
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