PSI - Issue 19

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Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2019) 000 – 000 Structural Integrity Procedia 00 (2019) 000 – 000

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Procedia Structural Integrity 19 (2019) 463–471

Fatigue Design 2019 Initiation and propagation of fatigue cracks from surface imperfections on 304L austenitic stainless steel P. Cussac a , C. Gardin a , V. Pelosin a , G. Hénaff a , L. de Baglion b , O. Ancelet b , S. Courtin c a Institut Pprime, Téléport 2, 1 avenue Clément Ader, 86961 Futuroscope Chasseneuil b Framatome, 1 Pl. Jean Millier 92400 Courbevoie, France c EDF R&D, 7 Boulevard Gaspard Monge, 91120 Palaiseau, France Given the stringent requirements of high levels of safety in nuclear components, stakeholders of French nuclear industry must anticipate the presence of residual surface imperfections in these components. Such imperfections could be introduced during manufacturing or maintenance operations. The incidence of surface irregularities on the fatigue strength of metallic components must be considered. Meanwhile, nuclear components are generally loaded under low-cycle fatigue and large-scale plasticity conditions. The present work aims at assessing the impact of a controlled surface irregularity on the fatigue life of typical nuclear materials. The influence of characteristic parameters under low-cycle fatigue conditions is also investigated. A 304L austenitic stainless steel used in components of French nuclear power plants was studied. Fatigue tests were conducted under fully-reversed total axial strain control in air at ambient temperature with total s train amplitudes ranging from Δε t /2 =0.2% to Δε t /2=0.6%. Surface irregularities, whose depth varies between 100 and 350 micrometers, have been introduced on polished cylindrical samples. The direct current potential drop method has been used to monitor the crack propagation, and thereafter, to derive crack growth rate data. Experimental markings of the crack front for different cycle numbers have been carried out to calibrate the variation of the potential as a function of crack depth. It appears that the fatigue life is strongly reduced in presence of a surface irregularity. Fatigue Design 2019 Initiation and propagation of fatigue cracks from surface imperfections on 304L austenitic stainless steel P. Cussac a , C. Gardin a , V. Pelosin a , G. Hénaff a , L. de Baglion b , O. Ancelet b , S. Courtin c a Institut Pprime, Téléport 2, 1 avenue Clément Ader, 86961 Futuroscope Chasseneuil b Framatome, 1 Pl. Jean Millier 92400 Courbevoie, France c EDF R&D, 7 Boulevard Gaspard Monge, 91120 Palaiseau, France Abstract Given the stringent requirements of high levels of safety i nuclear compo ents, stakeholders of French nuclear industry must anticipate the presence of residual surface imperfections in these components. Such imperfections could be introduced during anufacturing or maint nance operations. The incidence of surface irregularities on the fatigue strength of metallic components must be considered. Meanwhile, nuclear components are generally loaded under low-cycle fatigue and large-scale plasticity conditions. The present work aims at assessing the impact of a controlled surface irregularity on the fatigue life of typical nuclear materials. The influence of characteristic parameters under low-cycle fatigue conditions is also investigated. A 304L austenitic stainless steel used in components of French nuclear power plants was studie . Fatigue tests were conducted under fully-reversed total axial strain control in air at ambient temper ture with total s train amplitudes ranging from Δε t /2 =0.2% to Δε t /2=0.6%. Surface irregularities, whose depth varies between 100 an 350 micr meters, have been introduced on polished cylindric l samples. Th irect current potential drop met od has bee used to mo itor the crack propagation, and thereafter, to derive crack growth rat data. Experimental markings of the crack front for different cycle numbers have been carried out to calibrate the variation of the potential as a function of crack depth. It appears that the fatigue life is strongly reduced in presence of a surface irregularity. Abstract

© 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers.

Keywords: surface imperfections ; 304L ; low-cycle fatigue ; direct current potential drop method ; propagation ; fatigue life Keywords: surface imperfections ; 304L ; low-cycle fatigue ; direct current potential drop method ; propagation ; fatigue life

1. Introduction 1. Introduction

The continuing reinforcement of nuclear safety requirements is leading to a growing need for mechanical justification of components that requires industry stakeholders to anticipate and take into account all the problems that may arise. The surface imperfections presence on the nuclear components with regard to the phenomenon of fatigue The continuing reinforcement of nuclear safety requirements is leading to a growing need for mechanical justification of components that requires industry stakeholders to anticipate and take into account all the problems that may arise. The surface imperfections presence on the nuclear components with regard to the phenomenon of fatigue

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers.

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 10.1016/j.prostr.2019.12.050