The linear‐elastic Theory of Critical Distances to estimate high‐cycle fatigue strength of notched metallic materials at elevated temperatures

Abstract

This paper investigates the accuracy of the linear‐elastic Theory of Critical Distances (TCD) in estimating high‐cycle fatigue strength of notched metallic materials experiencing elevated temperatures during in‐service operations. The TCD postulates that the fatigue damage extent can be estimated by directly post‐processing the entire linear‐elastic stress field acting on the material in the vicinity of the crack initiation locations. The key feature of this theory is that the high‐cycle fatigue assessment is based on a scale length parameter that is assumed to be a material property. The accuracy of this design method was checked against a number of experimental results generated, under axial loading, by testing, at 250 °C, notched specimens of carbon steel C45. To further investigate the reliability of the TCD, its accuracy was also checked via several data taken from the literature, these experimental results being generated by testing notched samples of Inconel 718 at 500 °C as well as notched specimens of directionally solidified superalloy DZ125 at 850 °C. This validation exercise allowed us to prove that the linear‐elastic TCD is successful in estimating high‐cycle fatigue strength of notched metallic materials exposed to elevated temperature, resulting in estimates falling within an error interval of ±20%. Such a high level of accuracy suggests that, in situations of practical interest, reliable high‐cycle fatigue assessment can be performed without the need for taking into account those non‐linearities characterising the mechanical behaviour of metallic materials at high temperature, the used critical distance being still a material property whose value does not depend on the sharpness of the notch being designed.

Fracture Behavior of Nanoscale Notched Silicon Beams Investigated by the Theory of Critical Distances

“…In other words, failure may occur when on the net section the stress is close to σ UTS , as happens when plane specimens are considered. It is worth noting that, similar to the procedure summarized here, TCD has also been applied successfully under fatigue, [37,38] mixed-mode loading, [39] elevated temperature, [40] and elastic-plastic conditions. [41] The evaluation of the fracture toughness by the TCD in the form of the point method is based on stress analysis ahead of the notch root, as described earlier.…”

Advanced Materials for Applications at High Temperature: Fatigue Assessment by Means of Local Strain Energy Density

“…Recently, Louks and Susmel [22] presented some results from high-temperature fatigue tests conducted on C45notched specimens. The aim was to check the accuracy of linear-elastic TCD in estimating high-cycle fatigue strength of notches metals, when experiencing in service high temperature.…”

“…Recently, Louks and Susmel [22] investigated the accuracy of Theory of Critical Distances (TCD) in estimating high-cycle fatigue strength of notched metallic materials experiencing elevated temperatures during in-service operations. They checked the accuracy of TCD against a number of experimental results generated, under uniaxial loading, by testing at 250 C notched specimens made of carbon steel C45, as well as considering many data taken from the literature.…”

“…In detail, C45 carbon steel tested at 250 C, [22] Inconel 718 tested at 500 C, [19,20] and directionally solidified superalloy DZ125 at 850 C [21] have been considered. Different data taken from the literature have been considered and reanalyzed by means of the strain energy density averaged over a control volume.…”

Low Cycle Fatigue Behaviors of Alloy 617 (INCONEL 617) Weldments for High Temperature Applications

“…Plastic deformation is expected to play a major role in this process. Several researchers, e.g., Lazzarin, et al and Susmel, et al [17,18], have primarily considered a very high-temperature fatigue problem with the high cycle fatigue regime. This was initiated from the pioneering Coffin-Manson relationship as a definition of strain elements at LCF regime.…”