Crack Paths 2009

Specimens taken from the transition zone (specimens number”…-4” and “…-5” in

Fig. 3) contain a mixture martensite, bainite and ferrite. The fatigue behavior of the

hourglass specimens will depend strongly on the relative location of the notch root and

the various kinds of microstructure. This is part of an ongoing research.

C O N C L U S I O N

The fatigue behaviour of a shaft with local varying microstructure is studied. It is found

that the lifetime of specimens taken from the base material (ferrite/pearlite)

is well

approximated by a classical fracture mechanics analysis, even though multitudinous

microcracks are initiated. This implies that the damage accumulation process is growth

dominated. On the other hand, regions containing martensite have no visible surface

damage during fatigue loading, but fail as soon a crack of some hundred microns is

initiated.

A C K N O W L E D G E M E N T

This paper is based on studies carried out by the transregional collaborative research

centre SFB/TRT R R30, which is kindly supported by the GermanResearch Foundation

(DFG).

R E F E R E N C E S

1. Weidig U., Huebner K., Steinhoff K. Bulk steel products with functionally graded

properties produced by differential thermo-mechanical processing, Steel research

int 2008; 79 (1): 59-65.

2. Besel M., Brueckner-Foit A. Surface damage evolution of engineering steel,

Fatigue Fract Engng Mater Struct; accepted for publication 2008.

3. Fulland M., Steigemann M., Richard H.A., Specovius-Neugebauer M.

Numerische Bestimmung des Ermüdungsrisswachstums in inhomogenen

Materialien, DVM-Bericht 240, Zuverlässigkeit

von Bauteilen durch

bruchmechanische Bewertung: Regelwerke, Anwendungenund Trends, Deutscher

Verband für Materialforschung und -prüfung e. V., Berlin, 2008, pp.83-92.

4. Besel M., Brueckner-Foit A., Motoyashiki Y., Schäfer O. Lifetime distribution of

notched components containingvoid defects, Arch Appl Mech (2006) 76: 645–653

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