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The cyclic R-curve describes the resistance of a material to fatigue crack propagation fromthe short to the long crack regimes and it is therefore an essential ingredient in any fracturemechanics-based fatigue assessment procedure. This work presents different testing proceduresemployed in the experimental determination of the cyclic R-curve, especially focusing onthe comparison with long fatigue crack propagation thresholds obtained by means of thecompression precracking load reduction (CPLR) procedure. The tests were performed on theEA4T steel considering different stress ratios. The results show a good reproducibility of thecyclic R-curves at every stress ratio and for any testing procedure. In addition, the cyclicR-curves were used in a fracture mechanics-based assessment to predict the fatigue limits ofspecimens containing micro-notches.
This paper presents the application of short crack propagation models based on the cyclic R-curve for assessing the fatigue strength of additively manufactured (AM) materials containing fabrication defects. Chapetti’s and IBESS models were implemented in combination with Murakami’s √area parameter, considering recently published data on laser powder bed fusion processed AISI 316L stainless steels. Estimated S-N curves and Kitagawa-Takahashi diagrams predict fairly well the experimental data, especially the origin of the failure from internal or surface defects. These results provide an indication that the methods based on the cyclic R-curve constitute suitable tools for fatigue behavior assessment of AM materials.