Discussion of models for LCF small crack growth

Abstract

The life assessment for a component subjected to high strain concentration in critical regions can be treated as a crack growth estimation starting from the first cycle of the component life. This approach assumes that the presence of same small surface defects or slip bands causes a quickly crack nucleation in critical regions where Low Cycle Fatigue (LCF) design is adopted. The work is focused on the analysis of LCF tests carried out by the aim of smooth cylindrical specimens and specimens with semi-circular notches made of a quenched and tempered steel. The crack growth has been monitored using a thin acetate-foil based replica technique. Two different approaches have been analyzed in order to define a model able to predict the crack growth rate for high constant strain amplitudes. Such a tool is useful to assess the residual life of a component in presence of a crack in critical regions where high stress concentrations cause cyclic yielding of the material. Finally a new analytical model able to predict the crack growth rates is presented.