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

Abstract

The interest on fatigue assessment of steel and other alloys at high temperature has increased continuously in the last years. However, high cycle fatigue of notched components at high temperature has not been deeply investigated experimentally and theoretically. The present paper investigates the accuracy of Strain Energy Density (SED) averaged over a control volume approach when applied to high-temperature fatigue data from notched components. In the present work, a large bulk of high-temperature fatigue data, taken from the literature and regarding notched components made of different advanced materials, is reanalyzed. In detail: C45 carbon steel at 250°C, Inconel 718 at 500°C, and directionally solidified superalloy DZ125 at 850°C are considered. The main advantage of SED averaged over a control volume is that different geometries can be summarized in a single narrow scatter band. From an industrial viewpoint, the use of a geometry-independent parameter (and fatigue curve) leads to a considerable advantage in terms of time and cost

Creep behavior of V-notched components

“…The evaluation of stress and strain at some points ahead of the notch tip may be a possible way to address the problem. Different methods are available in literature dealing with this matter, for example based on energy local approaches such as Strain Energy Density [23][24][25]. This parameter could be useful also to characterize creeping conditions if combined with the present model, giving the possibility to include in the analysis also cracks and sharp V-notches.…”

A Review of the Fatigue Strength of Load Carrying Shear Welded Joints

“…The approach has subsequently been formalized for loading axis spider diagrams (Lazzarin et al, 2008b), as well as for the u-and blunt nicks V- (Lazzarin and Berto, 2005;, by means of the expressions obtained by Filippi et al (2002) for the fields of stress before the blunt notches and has been successfully applied on a wide range of materials and the conditions of loading (Berto and Lazzarin, 2014;. Recently, the EDI approach has been extended to the evaluation of the fatigue of specimens cut from Ti-6Of-4V under load axis spider diagrams and fatigue at high temperature alloy of copper-cobalt-beryllium , 4013.9 CrMoV steel (Gallo and Berto, 2015a; and level 2 (titanium Gallo et al, 2015).…”

Evaluation of the strain energy density control volume for a nanoscale singular stress field

“…Other important advantages can be achieved by using the SED approach. The most relevant are the following: The scale effect is considered in the SED formulation; It can be applied and defined for mode II, III and mixed mode condition; It overcomes the problem tied to the different NSIF units of measure in the case of different notch opening angles; In case of very thin structures, T‐stress is taken into account in the method; It directly includes three‐dimensional effect and out‐of‐plane singularities; It has been recently employed to assess high temperature fatigue of notched components, showing enormous potentialities also when non‐linear effects are taking place …”

“…• It can be applied and defined for mode II, III and mixed mode condition; • It overcomes the problem tied to the different NSIF units of measure in the case of different notch opening angles; • In case of very thin structures, T-stress is taken into account in the method; • It directly includes three-dimensional effect and outof-plane singularities; • It has been recently employed to assess high temperature fatigue of notched components, showing enormous potentialities also when non-linear effects are taking place. [36][37][38][39][40][41][42][43][44][45] Under the hypothesis that all the material inhomogeneities can be averaged, the SED approach showed to be a powerful tool both for static and fatigue strength assessment of notched and welded structures.…”