PSI - Issue 25

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ScienceDirect

Procedia Structural Integrity 25 (2020) 420–429 Structural Integrity Procedia 00 (2019) 000–000 Structural Integrity Procedia 00 ( 19) 00–000

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© 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 the VCSI1 organizers Abstract Flexible graphite is commonly used in a various range of applications in which high resilience, high thermal stability and chemical resistance are requested. Such material is obtained as the last stage of compression of exfoliated graphite flakes without any additive binder and its density is fundamental in determining all the mechanical, thermal and electrical properties. During the compression, the worm-like units interlock among each other by only friction forces and build connected clusters or structural units that retain their shape during the load application. The orientation of the latter changes together with the increase on density and gives an higher grade of anisotropy among the in-plane and out-of-plane directions. This process leaves a fraction of void volume that decreases together with the compaction pressure. A certain level of inherent porosity is therefore always present; this, together with the low thermal expansion comparable to that of metals, make such material excellent on dissipate deformation energy by mean of sliding among graphite layers. For the same reasons, the applications in the mechanical field request mainly the ability of work absorption in compression loading, like in sealing and dumping and moreover the visco-elastic properties are remarkable and comparable to those of rubbery materials. In this work an overview is given about the microstructure changing during the compression of the expanded phase and its e ff ect on the main mechanical properties. The values of the principal properties available in literature are compared. c 2020 The Authors. Published by Elsevier B.V. T is is an open access article under the CC BY- C-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) P r re ie lin : Peer-rev ew under responsibility of the VCSI1 organizers. Keywords: Flexible graphite ; Micro-structure ; Mechanical properties; Visco-elasticity. 1st Virtual Conference on Structural Integrity – VCSI1 echanical properties of flexible graphite: review E. Solfiti a , F. Berto a a Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology, Richard Birkelands vei 2b, Trondheim, 7491, Norway Abstract Flexible graphite is commonly used in a various range of applications in which high resilience, high thermal stability and chemical resistance are requested. Such aterial is obtained as the last stage of compression of exfoliated graphite flakes without any additive binder and its density is fundamental in determining all the mechanical, thermal and electrical properties. During the compression, the worm-like units interlock among each other by only friction forces and build connected clusters or structural units that retain their shape during the load application. The orientation of the latter changes together with the increase on density and gives an higher grade of anisotropy among the in-plane and out-of-plane directions. This process leaves a fraction of void volume that decreases together with the compaction pressure. A certain level of inherent porosity is therefore always present; this, together with the low ther al expansion comparable to that of metals, make such material excellent on dissipate defor ation energy by mean of sliding among graphite layers. For the same reasons, the applications in the mechanical field request mainly the ability of work absorption in compression loading, like in sealing and dumping and moreover the visco-elastic properties are remarkable and comparable to those of rubbery materials. In this work an overview is given about the microstructure changing during the compression of the expanded phase and its e ff ect on the main mechanical properties. The values of the principal properties available in literature are compared. c 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 line: Peer-review under responsibility of the VCSI1 organizers. Keywords: Flexible graphite ; Micro-structure ; Mechanical properties; Visco-elasticity. 1st Virtual Conference on Structural Integrity – VCSI1 Mechanical properties of flexible graphite: review E. Solfiti a , F. Berto a a Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology, Richard Birkelands vei 2b, Trondheim, 7491, Norway

1. Introduction 1. Introduction

Flexible graphite (FG) refers to as a low density graphitic material that was developed at the end of the 60s (Shane et al. (1968)) and later introduced in a wider range of industrial applications (Chung (1987, 2015). The commercial FG is mainly obtained by rolling of exfoliated graphite without any binder and it is usually tailored in foils or sheets with di ff erent thicknesses and densities. In some cases, even on academic purposes, simple uniaxial compression can be Flexible graphite (FG) refers to as a low density graphitic material that was developed at the end of the 60s (Shane et al. (1968)) and later introduced in a wider range of industrial applications (Chung (1987, 2015). The commercial FG is mainly obtained by rolling of exfoliated graphite without any binder and it is usually tailored in foils or sheets with di ff erent thicknesses and densities. In some cases, even on academic purposes, simple uniaxial compression can be

∗ Corresponding author. Tel.: + 39-3405863109 E-mail address: emanuele.solfiti@ntnu.no (E. Solfiti) ∗ Corresponding author. Tel.: + 39-3405863109 E-mail address: emanuele.solfiti@ntnu.no (E. Solfiti)

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 the VCSI1 organizers 10.1016/j.prostr.2020.04.047 2210-7843 c 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 line: Peer-review er responsibility of the VCSI1 organizers. 2210-7843 c 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 line: Peer-review under responsibility of the VCSI1 organizers.