The investigation considers the geomctrical size effect for hcat-treated 37Cr 4 stecl specimens in the case of one-level and multi-level fatigue tests. It was shown that the ratio Notch FactoriSCF of geometrically similar specimens increases asymptotically with the notch radius, tending to a value less than 1. Thc formula of Srieler for the ratio SCFi Notch Factor do not describe correctly the decrease of the fatigue limit with specimen diameter. A more exact description o f the size effect is obtained with the aid of a two-parameter formula, which takes into account the support effect of the cyclic strain hardening and of the stress gradient.An effcct of spccimen size on fatiguc life was also investigatcd in the case of multi-level tests. It seems that this effect is associated with a smaller diameter interval than the effect of size on the Fatigue limit. This is conncctcd with the higher plastification of the notclicd arca in programme tests with maximum stress much higher than the fatigue limit. The programme fatigue life and the damage sum were considerably larger for the smaller (d = 8.9 mm) than fur the larger (d = 22.26 mni) specimens. but further increase of thc specimen diameter see~ns to have a slight effect.
Rein geometrischer GroReneinfluR im
An drei warmfesten Stahlen wird das Kriecherinudungsverhalten erstmals rnit systematisch durchgeflihrten, dreistufigen betriebsahnlichen Dehnwechselversuchen bis 8000 h untersucht. Zur Ermittlung der rechnerischen Kriechermudungrtschadigung wird von der verallgemeinerten Schadensakkumulationshypothese ausgegangen. Die Schadensakkumulation erfolgt nach unterschiedlichen Zykluszahlverfahren.
Multi-stage service-type strain cycling of heat resistant steelsThe creep-fatigue behaviour of three heat resistant steels is investigated by service-type three-stage creep-fatigue tests up to 8000 h duration. Creep-fatigue damage is calculated on the basis of the generalized damage accumulation rule. Different cycle counting methods are taken into consideration.
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