PSI - Issue 42

Nikola Schmidová et al. / Procedia Structural Integrity 42 (2022) 1306–1313

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2 © 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 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

Keywords: Damage detection; Filament winding; Polymer-matrix composites; Electrical resistance measurement method

1. Introduction The electrical resistance (ER) measurement method has been under intensive investigation in recent years, see Schulte and Baron (1989). The measuring of electrical resistance has been used for strain monitoring and damage detection of various composite materials also by Todoroki et al. (2007). A fiber composite material with non conductive fibers and matrix has been doped with conductive particles, see Böger et al. (2008). It is not needed to add any conductive particles in a carbon fiber composites with non-conductive matrix, because of the conductivity of the fibers. Alignment of the fibers and random contact of the carbon fibers within the layers and between layers causes that the composite is conductive in all three dimensions as stated also in Todoroki et all (2002). The ER measurement method has been successfully used for impact damage detection by Wang et al (2005), delamination detection and fatigue. One of the problem which is still under investigation is the contact preparation on the structure. Usually the contacts are prepared on the surface (in case of cylindrical specimens on the outer surface), see Wang et al 2006 and Kwon et al 2016. A conductive epoxy is usually used for preparation of electrical contacts. The drawback of this methods is, that the surface of the specimen has to be polished before preparation of electrical contacts. Other method is conductive layer deposition, which has been used only for outer surfaces so far, see Ogawa et al. 2013. In our study we investigated possibility of electrical contact preparation on the internal surface of carbon fiber wound tubes in order to keep outer surface is intact. This requirement had to be met, because sometimes outer surface of investigated component can be used for cabling and also from the esthetical point of view. We prepared carbon fiber tows with nickel coating at the ends. These carbon fiber tows were integrated to the structure during manufacturing and served as electrical contacts to the structure. The symmetrical convex octagon shape specimens were manufactured using a filament winding technology. The specimens were manufactured with Integrated Loop Technology (ILT) joints at the ends in a single production step. This configuration of tubes with integrated joints allows very effective load transfer and it is also efficient from the manufacturing point of view. This type of components could be used for example in construction of robotic arms for automated processes. Two type of specimens were manufactured. Specimens with one ILT joint serve for flexural loading, see Fig. 1 (a), specimens with two ILT joints underwent torsional loading, see Fig. 1 (b).

2. Experimental procedure 2.1. Specimen preparation

The automated filament winding process was used for specimen manufacturing. The epoxy resin LG900/HG100 (GRM Systems s.r.o., Czech Republic) and carbon fibers T700 (Toray Composite Materials America, Inc., USA) were used. The specimens were manufactured by Compo Tech PLUS, spol. s.r.o. located in Czech Republic. The Carbon fibers with electrical conductive endings were integrated during manufacturing before the first filament wound layer. Each specimen was manufactured out of 5 layers.

(a)

(b)

Fig. 1 (a) Configuration of the flexural loading; (b) Configuration of the torsional loading.