Experimental Study on the Fatigue Life of Low-Carbon Steel DD11: Combination of Pre-Strain and Notch Effect

This paper is intended to study the fatigue behaviour of low-carbon steel DD11 with the combined effect of pre-strain and notch geometry, which are important in components working under cyclic loading in service. To this end, experimental fatigue tests were performed on specimens with different configurations: (i) specimens pre-strained to 24% (beyond the tensile strength point), (ii) specimens combining pre-strain and notch effects, and (iii) double-notched specimens, which feature a higher stress concentration factor. The experiments were complemented by numerical simulations and analytical formulations, and fracture surfaces were examined to support the interpretation of the results. The main results show that the applied pre-strain (24%) reduces the fatigue limit by 8.5% when compared to the un-notched case. However, when pre-strain and notch effects are combined, no significant additional influence on the fatigue limit is observed. In the double-notched configuration, a higher stress concentration factor is found compared to previous studies by the authors, leading to a reduction in the fatigue limit, with localised plasticisation similar to that observed in the compared scenario.