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Towards a temperature dependent and probabilistic lifetime concept for nodular ductile cast iron materials undergoing isothermal and thermo-mechanical fatigue

: Garcia Trelles, E.; Schweizer, C.; Eckmann, S.

Fulltext ()

Hénaff, G.:
12th International Fatigue Congress, FATIGUE 2018 : Poitiers Futuroscope, France, May 27-June 1st, 2018
Les Ulis: EDP Sciences, 2018 (MATEC Web of Conferences 165)
Art. 19006, 8 pp.
International Fatigue Congress (FATIGUE) <12, 2018, Poitiers>
European Commission EC
H2020; 634135; HERCULES-2
Conference Paper, Electronic Publication
Fraunhofer IWM ()
LCF; OPTMF; cyclic material behavior; intergranular embrittlement (IE)

In this investigation, the fatigue behaviour of a ductile cast iron with high content of silicon and molybdenum, was experimentally characterized by performing isothermal low cycle fatigue (LCF) tests as well as out-of-phase thermomechanical fatigue (OPTMF) tests within the temperature range RT – 500 °C. The studied material shows an embrittlement at temperatures nearby 400 °C. A possible explanation for the observed lifetime reduction is intergranular embrittlement (IE). A mechanism based lifetime model is proposed for assessing the lifetime. The model is based on the assumption that the crack advance per cycle is correlated with the cyclic crack tip opening displacement (ΔCTOD) attributed to the crack tip blunting caused by accumulation of plastic and creep deformations ahead of the crack tip. Intergranular embrittlement is accounted for by introducing a temperature and strain rate dependent prefactor in the crack growth law, which only acts in a certain temperature range. The model is calibrated for a GJS material and successfully applied to predict the lifetime of this material when undergoing isothermal and non-isothermal mechanical loadings. A probabilistic interpretation of the scatter of the investigated material is presented in conjunction with the random nature of the initial defect size distribution.