Fatigue behaviour prediction of steel reinforcement bars using an adapted Navarro and De Los Rios model

• Surface martensite contributes to the scatter reduction in rebars compared to ferrite–pearlite.
• The fatigue life of HR–CW and QST rebars is largely occupied by the growth of short cracks.
• The influence of microstructure and roughness on the scatter of rebars is about 50%, separately.

Fatigue cracks tend to initiate on the rebar surface and therefore, the surface conditions may control their fatigue behaviour. This study investigates the influence of surface microstructure and roughness dispersion on the scatter and fatigue life of hot rolled (HR)–cold worked (CW) and quenched and self-tempered (QST) rebars. The stochastic nature of the fatigue life is mainly affected by the scatter of short cracks in the crack initiation phase. A model adapted from Navarro and De Los Rios (N–R) was developed to predict the crack initiation, including short crack growth, and long crack propagation phases. The crack initiation phase includes the dispersion inherent to the grain size, grain orientation ratio and multiple phases i.e., ferrite–pearlite and martensite as well as the roughness dispersion determined on the rebar surface and the influence of the rib geometry. The stress concentration factor due to the rib geometry was considered as a constant parameter. In the long crack propagation phase, all microstructural features are considered as constants. The model results were compared to experimental data from the literature.