PSI - Issue 71

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ScienceDirect

Procedia Structural Integrity 71 (2025) 103–110

5 th International Structural Integrity Conference & Exhibition (SICE 2024) Effect of Proportional/ Non-Proportional Axial-Torsion Cyclic Loading on Fatigue Life of Notched Specimens of C-Mn Steel Shreebanta Kumar Jena 1,2* , Punit Arora 1,2 , Suneel K. Gupta 1,2 and J.Chattopadhyay 1,2 1 Reactor Safety Division, Bhabha Atomic research Centre (BARC), Mumbai, India 2 Department of Engineering Sciences, Homi Bhabha National Institute (HBNI), Mumbai, India Abstract The present study aims to present experimental results on notched tubes of C-Mn steel under proportional and non proportional axial-torsion cyclic loading conditions. Tubes with two different sizes of through-thickness circular holes in the gauge region of tube specimens were used for fatigue experiments. These tubes with circular holes have been subjected to remote in-phase (proportional) and out-of-phase (non-proportional) axial-torsion strain-controlled conditions. During the test, localized strain fields ahead of the hole have been measured using digital image correlation technique. The test fatigue lives under proportional and non-proportional loading conditions have been compared for the same set of remotely controlled axial and torsion strain amplitudes. The experimental fatigue life under non proportional conditions comes out to be higher than that of corresponding proportional loading conditions for such tubes with holes and same remote loading conditions.

∗ Corresponding author. Mob.: +7205281180; E-mail address: shreebantaodisha@gmail.com

Keywords: Proportional; Non-Proportional; Digital Image Correlation; Fatigue crack initiation . © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SICE 2024 organizers

1. Introduction Critical structural components of automobile, aviation and Nuclear Power Plants (NPP) industries are at time subjected to multiaxial cyclic loading excursions. The multiaxiality in structural components can be either due to presence of geometric discontinuity or arises because of complex applied loading source(s). Structural components having notch/discontinuity, always experience multiaxial state of stress/strain at/ahead of the discontinuity location irrespective of the remote loading scenario (uniaxial/multiaxial). This multiaxial cyclic stress/ strain state can be either proportional (with fixed principal stress directions) or non-proportional (with varying principal stress directions). It is widely reported and well understood that when structural components are subjected to non-proportional loading conditions, some material experiences additional hardening. This additional hardening effect was first noticed by Taira et al. (1968), later explained by Lamba and Sidebottom (1978) and Kanazawa et al. (1979). It takes place because of movement of crystallographic plane due to rotation as well as interaction of maximum shear plane. Further, it has been suggested by

2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SICE 2024 organizers 10.1016/j.prostr.2025.08.015