Fracture mechanics based assessment of the fatigue strength: approach for the determination of the initial crack size

Abstract

In a number of previous papers, the authors have proposed a model for fracture mechanics based prediction of the S‐N characteristics of metallic components with large microstructural defects. Here, an extension to materials that do not show large defects onto the fracture surfaces is provided. In such cases, an approach based on a so‐called cyclic R‐curve analysis is proposed for the determination of the initial flaw size, which has to be used in the calculation of fatigue crack propagation. The principle is explained and demonstrated by a first application to a welded joint.

Fatigue damage criteria classification, modelling developments and trends for welded joints in marine structures

“…Lassen 1990;Verreman and Nie 1996;Darcis et al 2006;Zhang and Maddox 2009;Hobbacher 2010;Chattopadhyay et al 2011;Zerbst and Madia 2015) and (calculation) values decreased from 1.00 [mm] down to 0.05 [mm], meaning even for welded joints, although the life time is often assumed to be growth dominated, the crack initiation contribution to the total life time increases, in particular in the HCF region.…”

Application of the cyclic R-curve method to notch fatigue analysis

“…The potential drop is known to be a very reliable method, but it is questioned by some researcher to provide poor or even not reliable values during test conducted at negative stress ratios. The author of this paper provided in a previous work [14] some comparison between single-specimen tests, in which the potential drop technique has been used, and the multi-specimen technique for SENB specimen tested at R = À1. No evidence of a strong dependence of the experimental values on the test methodology has been found.…”

“…The authors of this paper took advantage of this property of the R-curve analysis to propose a methodology for the determination of the initial crack length a i and the subsequent prediction of the fatigue limit in case of weld joints [14].…”

“…To this purpose, a procedure previously developed by the authors has been employed [14] and modified in order to deal with notches. The calculations are based on the cyclic R-curve method, in which the crack driving force has been calculated according to elasticplastic fracture mechanics in order to deal with mechanically short cracks.…”

Prozessmodell zum Einbringen von Eigenspannungen durch Festwalzen

“…Ein kürzlich erschienener Überblick über Betriebsfestigkeit und Schadenstoleranz von Radsatzwellen weist unter anderem auf die Bildung von Ermüdungsrissen an Korrosionsgrübchen, Steinschlägen (welche auf Hochgeschwindigkeitsstrecken erhöht auftreten) und an nichtmetallischen Einschlüssen hin . An Gegenmaßnahmen wird neben Beschichtungen zur Vermeidung von Korrosion und Steinschlag auf eine Erhöhung der metallurgischen Reinheit wie Elektroschlacke‐Umschmelzen sowie auf Wärmebehandlungen und Festwalzen zum Einbringen von Druckeigenspannungen verwiesen.…”