PSI - Issue 42

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

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Structural Integrity Procedia 00 (2019) 000 – 000

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Procedia Structural Integrity 42 (2022) 1600–1606

23 European Conference on Fracture - ECF23 Digital image correlation for accurate strain measurement on sharp notched specimens Koščo, T. a *, Ďurka, R . a a Slovak Univetsity of Technology, Faculty of Mechanical Engineering, Námestie slobody 17, Bratislava 812 31, Slovakia Abstract Notch stress concentration and the notch effects in general, play a significant role in the field of structural mechanics. Also, the strain measurement in notches is still a challenge. In cases, when the notch geometry is not exactly defined e.g., weld joints etc., the measurement of strains in notches becomes even more important. Therefore, the present work focuses on the problem of strain measurement on notched specimens, especially on sharp notches (notches with small minimum radius) by using the digital image correlation method. Initial measurements were carried out on specimens with known stress concentration and the results were compared with the analytical and numerical solution. Multiple camera positions with respect to the specimen are compared and discussed. Minimum number of pixels per notch radius for accurate measurement was determined based on the measured data. This limitation is influenced by several effects. The presented work focuses deeper on the influence of postprocessing filter methods. Several possible solutions to overcome this limitation are presented. The obtained results and the knowledge gained by previous measurements were utilized by direct practical measurements, weld notch stress concentration measurement. 23 European Conference on Fracture - ECF23 Digital image correlation for accurate strain measurement on sharp notched specimens Koščo, T. a *, Ďurka, R . a a Slovak Univetsity of Technology, Faculty of Mechanical Engineering, Námestie slobody 17, Bratislava 812 31, Slovakia Abstract Notch stress concentration and the notch effects in general, play a significant role in the field of structural mechanics. Also, the strain measurement in notches is still a challenge. In cases, when the notch geometry is not exactly defined e.g., weld joints etc., the measurement of strains in notches becomes even more important. Therefore, the present work focuses on the problem of strain measurement on notched specimens, especially on sharp notches (notches with small minimum radius) by using the digital image correlation method. Initial measurements were carried out on specimens with known stress concentration and the results were compared with the analytical and numerical solution. Multiple camera positions with respect to the specimen are compared and discussed. Minimum number of pixels per notch radius for accurate measurement was determined based on the measured data. This limitation is influenced by several effects. The presented work focuses deeper on the influence of postprocessing filter methods. Several possible solutions to overcome this limitation are presented. The obtained results and the knowledge gained by previous measurements were utilized by direct practical measurements, weld notch stress concentration measurement.

© 2022 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 scientific committee of the 23 European Conference on Fracture – ECF23 © 2020 Th Authors. Publish d by Elsevier B.V. This is an open access article und r the CC BY-NC-ND license (http://creativecommons.o g/licenses/by-nc-nd/4.0/) Peer-review under responsibility of 23 European Conference on Fracture - ECF23 Keywords: digital image correlation; notched specimen; welded specimen © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of 23 European Conference on Fracture - ECF23 Keywords: digital image correlation; notched specimen; welded specimen

1. Introduction Digital image correlation (DIC) has attracted the attention of experimental mechanics research community in last decades. Possibility of non-contact full-field measurements of displacement and strain field pushes the boundaries in the field of experimental mechanics and structural integrity as well. The main advantages over conventional methods e.g., strain gages, is the ability to accurately quantify the strain gradients and strain peaks. Strain peaks, especially by open-hole tensile test has been a challenge from the beginnings of DIC. Main drawback of conventional subset based DIC is the problem with image registration on the specimen edge that causes a loss of result on the edge, the notch root. Several solutions to overcome this problem has been proposed, such as extrapolation approach by Wang (2013), variable subset DIC algorithm proposed by Ma (2021) or finite element formulation for DIC method by Sun (2005), to overcome previously mentioned problem on the edge. Arise of stereo DIC systems 1. Introduction Digital image correlation (DIC) has attracted the attention of experimental mechanics research community in last decades. Possibility of non-contact full-field measurements of displacement and strain field pushes the boundaries in the field of experimental mechanics and structural integrity as well. The main advantages over conventional methods e.g., strain gages, is the ability to accurately quantify the strain gradients and strain peaks. Strain peaks, especially by open-hole tensile test has been a challenge from the beginnings of DIC. Main drawback of conventional subset based DIC is the problem with image registration on the specimen edge that causes a loss of result on the edge, the notch root. Several solutions to overcome this problem has been proposed, such as extrapolation approach by Wang (2013), variable subset DIC algorithm proposed by Ma (2021) or finite element formulation for DIC method by Sun (2005), to overcome previously mentioned problem on the edge. Arise of stereo DIC systems

* Corresponding author. Tel.: +421910670667. E-mail address: tomas.kosco@stuba.sk * Corresponding author. Tel.: +421910670667. E-mail address: tomas.kosco@stuba.sk

2452-3216 © 2022 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 scientific committee of the 23 European Conference on Fracture – ECF23 10.1016/j.prostr.2022.12.202 2452-3216 © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of 23 European Conference on Fracture - ECF23 2452-3216 © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of 23 European Conference on Fracture - ECF23