PSI - Issue 65

ScienceDirect Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2024) 000–000 Available online at www.sciencedirect.com Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2024) 000–000

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

Procedia Structural Integrity 65 (2024) 215–224

The 17th International Conference on MECHANICS, RESOURCE AND DIAGNOSTICS OF MATERIALS AND STRUCTURES (MRDMS 2023) Development of non-linearity of stress-strain dependencies in hysteresis loops during repeated uni-axial quasi-static tensile testing of unidirectional CFRP P.B. Severov* Mechanical Engineering Research Institute of the Russian Academy of Sciences, 4, M. Kharitonyevskiy Pereulok, Moscow 101990, Russia The purpose of this study is to investigate the degradation of the mechanical properties of carbon fiber-reinforced plastic (CFRP) under repeated loading, while simultaneously monitoring damages accumulation using the acoustic emission method. In the first part, the issues of the development of the non-linearity of stress-strain diagrams in the hysteresis loops of unidirectional CFRP under repeated uni-axial quasi-static tensile loading in the direction of highest stiffness are considered. Hysteresis loops were identified and the equations of the upper and lower branches were compiled. The linear and nonlinear components of these equations were determined. Non-linear elasticity is disrupted in the sections of active deformation due to intense damages. The preservation of non-linear elasticity occurs in the sections of passive deformation with minor damages. A sign of the transition of the material to a state of pre-destruction is the formation of a second extremum in the non-linear component of the upper branch. © 2024 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 MRDMS 2023 organizers Keywords: Unidirectional carbon fiber-reinforced plastic (CFRP); mechanical hysteresis; quasi-elasticity; damages accumulation The 17th International Conference on MECHANICS, RESOURCE AND DIAGNOSTICS OF MATERIALS AND STRUCTURES (MRDMS 2023) Development of non-linearity of stress-strain dependencies in hysteresis loops during repeated uni-axial quasi-static tensile testing of unidirectional CFRP P.B. Severov* Mechanical Engineering Research Institute of the Russian Academy of Sciences, 4, M. Kharitonyevskiy Pereulok, Moscow 101990, Russia Abstract The purpose of this study is to investigate the degradation of the mechanical properties of carbon fiber-reinforced plastic (CFRP) under repeated loading, while simultaneously monitoring damages accumulation using the acoustic emission method. In the first part, the issues of the development of the non-linearity of stress-strain diagrams in the hysteresis loops of unidirectional CFRP under repeated uni-axial quasi-static tensile loading in the direction of highest stiffness are considered. Hysteresis loops were identified and the equations of the upper and lower branches were compiled. The linear and nonlinear components of these equations were determined. Non-linear elasticity is disrupted in the sections of active deformation due to intense damages. The preservation of non-linear elasticity occurs in the sections of passive deformation with minor damages. A sign of the transition of the material to a state of pre-destruction is the formation of a second extremum in the non-linear component of the upper branch. © 2024 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 MRDMS 2023 organizers Keywords: Unidirectional carbon fiber-reinforced plastic (CFRP); mechanical hysteresis; quasi-elasticity; damages accumulation © 2024 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 MRDMS 2023 organizers Abstract

1. Introduction 1. Introduction

The application of external forces on a solid can cause internal, localized injuries in the material's structure, leading to a redistribution of the stress-strain state of the material. Such structural injuries are commonly referred to as the damages of material. Fixing the flow of damages at an arbitrary point in time defines the concept of the level The application of external forces on a solid can cause internal, localized injuries in the material's structure, leading to a redistribution of the stress-strain state of the material. Such structural injuries are commonly referred to as the damages of material. Fixing the flow of damages at an arbitrary point in time defines the concept of the level

* Corresponding author. Tel.: +7-916-516-39-99. E-mail address: alpinprom@yandex.ru * Corresponding author. Tel.: +7-916-516-39-99. E-mail address: alpinprom@yandex.ru

2452-3216 © 2024 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 MRDMS 2023 organizers 2452-3216 © 2024 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 MRDMS 2023 organizers

2452-3216 © 2024 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 MRDMS 2023 organizers 10.1016/j.prostr.2024.11.033