Issue 50

A. Sarkar et alii, Frattura ed Integrità Strutturale, 50 (2019) 86-97; DOI: 10.3221/IGF-ESIS.50.09 86 Focused on Showcasing Structural Integrity Research in India Crack growth based life prediction approach under LCF-HCF interaction A. Sarkar, A. Nagesha, R. Sandhya Fatigue Studies Section, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu, India-603102 aritra@igcar.gov.in, https://orcid.org/0000-0002-8438-320X nagesh@igcar.gov.in,h ttps://orcid.org/0000-0002-2025-8100 san@igcar.gov.in M. Okazaki Department of Mechanical Engineering, Nagaoka University of Technology, Japan-940-2188 okazaki@mech.nagaokaut.ac.jp, https://orcid.org/0000-0001-7071-0399 A BSTRACT . 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 ( a cr ) exists, beyond which the LCF-HCF interaction becomes significant. An attempt was made to predict life under block cycling by estimating the a cr using fatigue crack threshold ( ΔK th ) 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 ( a cr.,eq ) which incorporates the damage contribution from DSA and ratcheting under combined LCF-HCF loading, was proposed for life estimation.. K EYWORDS . LCF; HCF; LCF-HCF interaction; Crack growth; 316LN SS. Citation: Sarkar, A., Nagesha, A., Sandhya, R., Okazaki, M., Crack growth based life prediction approach under LCF-HCF interaction, Frattura ed Integrità Strutturale, 50 (2019) 86-97. Received: 26.11.2018 Accepted: 24.06.2019 Published: 01.10.2019 Copyright: © 2019 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION 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. Currently, 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 M