Progress in the measurement of the cyclic R-curve and its application to fatigue assessment

The cyclic R-curve describes the resistance of a material to fatigue crack propagation from the short to the long crack regimes and it is therefore an essential ingredient in any fracture mechanics-based fatigue assessment procedure. This work presents different testing procedures employed in the experimental determination of the cyclic R-curve, especially focusing on the comparison with long fatigue crack propagation thresholds obtained by means of the compression precracking load reduction (CPLR) procedure. The tests were performed on the EA4T steel considering different stress ratios. The results show a good reproducibility of the cyclic R-curves at every stress ratio and for any testing procedure. In addition, the cyclic R-curves were used in a fracture mechanics-based assessment to predict the fatigue limits of specimens containing micro-notches.