PSI - Issue 39

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

www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia

Procedia Structural Integrity 39 (2022) 450–459

© 2021 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 CP 2021 – Guest Editors Abstract In this paper a set of specimens, used for the critical distance determination, are investigated with a non-contact 3D optical profiler. The fatigue fracture surfaces of both plain and V-notched specimens, under axial (mode I) and torsional (mode III) loadings are observed, investigating steel 42CrMo4+QT and aluminium alloy 7075-T6. The fatigue fracture profiles are compared to be previously obtained critical distances, both for mode I and mode III. The stage I to stage II transition was found at a smaller size than the axial critical distance, for the steel, while for the torsional load a local plateau at the nucleation was observed. The fracture surface of the axial loading was instead much irregular at the scale of the mode I critical distance, for the aluminium alloy, resembling a not concluded stage I, while again a relatively flat surface was observed for the mode III loading. © 2021 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 CP 2021 – Guest Editors Keywords: Fatigue fracture surface; 3D optical profile; Theory of critical distances; mode I and mode III loadings. 1. Introduction The recent research on the fatigue strength of materials focuses on the definition of a material length which can be considered the size of a process volume, where the stress and strains according to different criteria need to be averaged instead of just considering the maximum values at the notch tip. According to the Theory of Critical Distances (TCD), this length is a material property, however, it also depends on the load ratio, and most importantly on the load type. For these reasons, an accurate and reliable determination of the critical distance is recommended for an effective 7th International Conference on Crack Paths Fatigue fracture surface investigations with a 3D optical profiler C. Santus a *, P. Neri a , L. Romoli b , A. Lutey b , S. Raghavendra c , M. Benedetti c a University of Pisa, DICI – Largo Lucio Lazzarino, 1 – 56122 – Pisa, Italy b University of Parma, DIA – Parco Area delle Scienze, 181/A – 43124 – Parma, Italy c University of Trento, DII – Via Sommarive, 9 – 38123 – Povo (TN), Italy Abstract In this paper a set of specimens, used for the critical distance determination, are investigated with a non-contact 3D optical profiler. The fatigu fracture urfaces of both plain and V-notched sp cimens, under axial (mode I) and torsional (mode III) lo dings are observed, inves igating steel 42CrMo4+QT and aluminium alloy 7075-T6. The fatigue fracture profiles ar comp red to b previously obtained critical distances, both for mode I a d ode III. The stage I to sta e II t nsition was found at a smaller siz than the axial cr tical d stance, for the steel, while for the torsi nal load a loc l pla eau t the nucleation s bserved. The fractur surface of the axial loadi g was instead much irregular at the scale of the mode I critical distance, for the aluminium lloy, resembling a not conclu ed stage I, while again a elatively flat surf ce was observ d fo he mode III loading. © 2021 The Au hors. 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 u der re ponsibility of CP 2021 – Guest Editors Keywords: Fatigue fracture surface; 3D optical profile; Theory of critical distances; mode I and mode III loadings. 1. Introduction The recent research on the fatigue strength of materials focuses on the definition of a material length which can be conside d the size of a proc ss vol me, where the str ss and strains accor ing to different criteria need to be averaged instea of just considering th maxi um valu s at the notch tip. According to the Th ory of Crit cal Dis ances (TCD), this length i a material prop rty, however, it also d pends on the l a rati , and most impo tantly on the load type. For these reasons, an accurate and reliable determination f t critical dist ce is recomme ded for an effective 7th International Conference on Crack Paths Fatigue fracture surface investigations with a 3D optical profiler C. Santus a *, P. Neri a , L. Romoli b , A. Lutey b , S. Raghavendra c , M. Benedetti c a University of Pisa, DICI – Largo Lucio Lazzarino, 1 – 56122 – Pisa, Italy b University of Parma, DIA – Parco Area delle Scienze, 181/A – 43124 – Parma, Italy c University of Trento, DII – Via Sommarive, 9 – 38123 – Povo (TN), Italy

* Corresponding author. Tel.: +39-(0)50-2218007. E-mail address: ciro.santus@unipi.it * Corresponding author. Tel.: +39-(0)50-2218007. E-mail address: ciro.santus@unipi.it

2452-3216 © 2021 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 CP 2021 – Guest Editors 2452-3216 © 2021 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 u der responsibility of CP 2021 – Guest Editors

2452-3216 © 2021 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 CP 2021 – Guest Editors 10.1016/j.prostr.2022.03.114