Abstract
The paper is concerned with localized fatigue performance improvement by means of a hole expansion technique. In order to explain this effect a theoretical model is proposed containing potentially important factors such as a residual stress σ r (strain ε r) induced by an uneven plastic deformation, stress-strain curve origin transformation σ t′ microstructural changes evoked by plastic deformation ΔSand secondary (technological) factors Δ tech. Based on Haigh's diagram and the material stress-strain curve it is concluded that the expanding process has an optimum that can be characterized by the optimal residual strain ε r,opt in the hole root material volume. A method is proposed for estimating its value, yielding the maximum fatigue life enhancement.
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