PSI - Issue 28

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

www.elsevier.com/locate/procedia

ScienceDirect

Procedia Structural Integrity 28 (2020) 1787–1794

1st Virtual European Conference on Fracture Observations of cleavage initiation in ferritic steel M. Ford a,b *, A. P Jivkov a , P. M. James b a Department of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester, M13 9PL, UK b Jacobs, Walton House, Risley, Warrington, WA3 6GA, UK

© 2020 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 the European Structural Integrity Society (ESIS) ExCo Abstract Local Approach (LA) to cleavage fracture models have been under development since the 1980s with the aim of predicting cleavage fracture, including accounting for the effects of temperature, crack-tip geometry and irradiation. This work presents observations of particle behaviour and micro-crack nucleation under stress conditions similar to those ahead of a crack-tip, achieved by testing bespoke tensile specimens with a highly constrained volume at temperatures in the material’s ductile to brittle transition region. This region was examined post-test using a scanning electron microscope to identify and characterise micro-cracks and micro crack initiation defects, such as particles. Supporting finite element analyses were performed to predict the mechanical fields acting on the defects. The results suggested that:  micro-cracks nucleated in the form of damaged, spherical regions around the initiation particle with a cloud of crack-tips, rather than as single penny shaped cracks as assumed in LA models;  these damaged regions can be much larger than the initiating particle;  nucleation was more often caused by failure of the particle-matrix interface than particle cracking. © 2020 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 the European Structural Integrity Society (ESIS) ExCo Keywords: Cleavage fracture; Local approach; Micro-crack 1. Introduction The ability to predict changes of cleavage fracture toughness (CFT) with temperature, crack-tip geometry and irradiation is critical to safety assessment and life extension of structural components. Global approaches to cleavage A b b h a C-N ce ti

©

* Corresponding author. Tel.: +44-1925-462617. E-mail address: michael.ford-2@postgrad.manchester.ac.uk

2452-3216 © 2020 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 the European Structural Integrity Society (ESIS) ExCo

2452-3216 © 2020 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 the European Structural Integrity Society (ESIS) ExCo 10.1016/j.prostr.2020.10.156