PSI - Issue 60

Shreebanta Kumar Jena et al. / Procedia Structural Integrity 60 (2024) 115–122 Author name / StructuralIntegrity Procedia 00 (2019) 000 – 000

116

2

by Jena et al. (2021).These difference in values of stress/strain amplitude at localized (at notch tip) and remote location bound to set up stress/strain gradient in presence of notch and discontinuityas investigated by Jena et al. (2022-2023). Further, it is reported and well understood that the extent of strain gradient present ahead of the notch tip invariably affect the fatigue life of components with notch/discontinuity. In that regard, a very limited test investigations are available in the literature where the strain gradient effect on fatigue life has been brought out by conducting tests under identical remote loading condition on different sizes of notched specimen. Gladskyi et al (2013) investigated notch effect as well as studied the load sequence effect on fatigue life under cyclic pure axial and pure torsion loading condition on thin-walled tube specimen with a transverse hole. Gates et al (2014,2016) analyzed the notch deformation behaviour on multiaxial fatigue by performing load-controlled tests on three different types of notches (notched tubular, stepped and grooved shaft specimen) for two different type of material(2023-T3 aluminum alloy & 1141 steel). Sakane et al. (2011) studied the notch effect on multiaxial fatigue behaviour by performing strain controlled test on V-notched solid shaft with three different notch root radii. Gao et al. (2010) investigated the notch effect on fatigue life by conducting extensive load-controlledtests on notched solid shaft of 16MNR steel under axial, torsional, In-phase axial torsional and Out of phase axial torsional loading condition. Additionally, Jiang and Fatemi-Socie critical plane model has also been used for fatigue life prediction. Most recently, Su and Zhu (2022) investigated the notch effect on fatigue life by carrying out stress-controlled fatigue test on tubular specimen with a single through thickness hole (notch size has been varied from 1mm to 4mm) and multiple through thickness hole (no of holes varies from 1 to 3) in the gauge region. These above test methodologies bring out the combined effect of peak strain amplitude and strain gradient on fatigue life. Recently, Jena et al. (2023) has proposed a new test methodology which brought out the individual effect of peak equivalent strain and stain gradient on fatigue life by conducting tests on notched tube specimen under remote axial loading condition and highlights the need for pretest FE analyses. However, this test methodology was demonstrated under remote pure axial conditions. The present study is aimed at extension of proposed test methodology of Jena et al. (2023) under remote pure torsion conditions. In view of this, the remote torsion strain amplitude has been so controlled for different hole sizes on tube specimens such that peak equivalent strain amplitude at the hole tip is nearly same. The present study also includes the use of Digital Image Correlation (DIC) and Strain Gauge (SG) techniques for localized strain measurements. Use of DIC technique for localized strain measurements on curved notched geometries has been hardly reported in literature. Further, the fatigue life assessment has been performed using theory of critical distance and critical plane-based models. Nomenclature NPP Nuclear Power Plant DIC Digital Image Correlation SG Strain Gauge IPHWR Indian Pressurized Heavy Water Reactor TTM Tension Torsion Machine LCF Low Cycle Fatigue FEA Finite Element Analyses FDP Fatigue Damage Parameter

N i , N p Test and Predicted fatigue life ̅ Equivalent strain amplitude Shear strain

* Corresponding author. Tel.: 222-2559-7139; fax: +0-000-000-0000 E-mail address: shreebantaodisha@gmail.com/skjena@barc.gov.in 2. Structure

Low cycle fatigue tests have been conducted on mirror polished small scale 1 inch diameter tube specimens having different size of through holes (of diameters as 3mm, 5.5mm and 8mm) circular hole. The present tests have been conducted under remote pure torsional strain-controlled conditions in air environment at ambient temperature (~28 ℃ ).