PSI - Issue 26

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 26 (2020) 277–284

© 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 MedFract1 organizers Abstract This study presents the results of Pressure Stimulated Currents (PSC) analysis using non-extensive statistical physics (NESP) approach when marble and amphibolite specimens were subjected to mechanical stress up to fracture. The specimens were subjected to a constant uniaxial stress, interrupted by an abrupt step-wise stress increase (Step-Stress Technique - SST) while concurrently the PSC emission was recorded. The loading protocol involved eight sequential steps of mechanical stress at a gradually higher level until the failure of the specimens. After each step, the stress was maintained constant until the PSC signal was restored to a final low value. After the PSC restoration the next stress step was applied. The recorded PSC temporal relaxation when the stress remained c onstant, was analyzed under the concept of NESP based on Tsallis’ entropy and the behavior of the entropic index q was studied for various stress levels. Throughout each next loading step at higher level, the entropic index q shows a progressive increase f rom 1.15 to 1.40 until the stress attains about 85% of the specimens’ total strength where it reaches a maximum value close to 1.4. When the applied stress becomes higher than the 85% of the specimens’ total strength, the entropic index q gradually decreases. It should be noted that this peak along with the subsequent decline of q coexists with the excessive damage development in the specimens’ bulk due to the applied mechanical stress. Taking into consideration the fact that the entropic index q quantifies the self-organization of the system, this behavior of q, for stress levels higher than 85% of the specimens’ ultimate stress strength, clearly corresponds to dynamic processes that dominate the system and guide the upcoming fracture. The above findings advocate the use of the entropic index q as a pre-failure indicator of the upcoming specimen fracture. © 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 MedFract1 organizers Keywords: Pressure Stimulated Currents; Amphibolite; Marble; Non-destructive testing; Tsallis entropy The 1 st Mediterranean Conference on Fracture and Structural Integrity, MedFract1 The relaxation processes of Pressure Stimulated Currents under the concept of Non-extensive statistical physics Andronikos Loukidis*, Ilias Stavrakas, Dimos Triantis Electronic Devices and Materials Laboratory, Department of Electrical and Electronics Engineering, University of West Attica, 250 Thivon Avenue, 122 44, Athens, Greece

* Corresponding author. Tel.: +306980162991 E-mail address: a.loukidis@uniwa.gr

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 MedFract1 organizers

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 MedFract1 organizers 10.1016/j.prostr.2020.06.035