Abstract
Prediction of cyclic life under low cycle fatigue - high cycle fatigue (LCF-HCF) interaction is of paramount importance in the context of structural integrity of components in the primary side of fast reactors where such damage under LCF-HCF interaction occurs. The present investigation deals with the crack growth behavior of a type 316LN austenitic stainless steel subjected to simultaneous application of LCF and HCF cycles (block-loading). Tests were performed over a wide range of temperatures from ambient to 923 K. Experimental results indicate that a critical crack-length (acr) exists, beyond which the LCF-HCF interaction becomes significant. An attempt was made to predict life under block cycling by estimating the acr using fatigue crack threshold (ΔKth) since the latter is known to be affected significantly by the loading history. A universal equation, based on the concept of an equivalent critical crack length (acr.,eq) which incorporates the damage contribution from DSA and ratcheting under combined LCF-HCF loading, was proposed for life estimation.
Highlights
M ost of the current investigations pertaining to the fatigue behavior of structural materials are dedicated to either low cycle fatigue (LCF) or high cycle fatigue (HCF) loading even though it is a well known fact that engineering components experience a varying load history throughout their service life
This is a significant issue in sodium-cooled fast reactors (SFRs) where components of the primary sodium circuit are prone to damage induced by LCF as well as HCF which can lead to a significant reduction in
It may be noted that the present tests are carried out at fixed LCF strain amplitude of ±0.6%, varying only the HCF cycles superimposed on it (Bs)
Summary
M ost of the current investigations pertaining to the fatigue behavior of structural materials are dedicated to either low cycle fatigue (LCF) or high cycle fatigue (HCF) loading even though it is a well known fact that engineering components experience a varying load history (interaction between LCF and HCF) throughout their service life. A major limitation of DCA is its semi-empirical nature which does not account for some intrinsic factors like crack length Such disadvantages will become more prominent at extreme conditions such as elevated temperature LCFHCF interactions. The block-loading experiments including combinations of both LCF and HCF are specially designed so that crack-growth based life-prediction models can be developed based on the same
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