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Can the spectrum-fullness be considered within a fatigue life assessment?
: Sonsino, C.M.; Oppermann, H.

Konstruktion (2011), No.7-8, pp.75-82
ISSN: 0373-3300
ISSN: 0720-5953
Journal Article
Fraunhofer LBF ()

Designing against service spectrum loading aims always at lightweight components. In this context the spectrum fullness plays a major rote with regard to the position of the Gassner-line, i.e. the fatigue life under variable amplitude loading. For this, fatigue life estimations are carried out mostly by the Palmgren-Miner rule with the modification of the Woehler-line because of its simpleness. Allowable damage sums suggested are significantly smaller than the theoretical damage sum D th = 1.0, which results definitely only by the fullest spectrum, namly under constant amplitude loading. However, since some years there are attempts to increase the allowable damage sums D al = 0.3 respectively 0.1 by considering the fullness of the applied spectrum. In the present paper the relation between the real damage sum and the fullness index is investigated. For this, fatigue tests under constant and variable amplitude loadings with Gaussian and straight-line amplitude distributions are evaluated. These tests were carried out under bending loading in multispecimen test rigs with fillet notched round bars made of the forged, quenched and tempered steels Ck 45 V (SAE 1045) and 42 CrMo 4 V (SAE 1042). However, a reliable consideration of a fullness index for correcting allowable damage sums is within the big scattering of the real damage sums not recommendable.