Issue 38

S. Hörrmann et alii, Frattura ed Integrità Strutturale, 38 (2016) 76-81; DOI: 10.3221/IGF-ESIS.38.10 76 Focussed on Multiaxial Fatigue and Fracture The effect of ply folds as manufacturing defect on the fatigue life of CFRP materials S. Hörrmann, A. Adumitroaie, M. Schagerl Christian Doppler-Lab for Structural Strength Control of Lightweight Constructions, Institute of Structural Lightweight Design, Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz, Austria susanne.hoerrmann@jku.at, http://orcid.org/0000-0001-7690-328X adi.adumitroaie@jkt.at, http://orcid.org/0000-0002-0812-5671 martin.schagerl@jku.at A BSTRACT . Manufacturing defects are inherent to any manufacturing process. However, in composite materials they might be unavoidable, e.g. ply waviness or even folds of plies are present in complex shaped parts during high pressure resin transfer molding of carbon fiber reinforced polymers. In this work, the effect of the ply folds on the fatigue life of the composite material is investigated. Folds along fiber direction (as they commonly appear during manufacturing) were artificially introduced in unidirectional non crimp fabric plies. The target of this study is the prediction of damage initiation due to this particular type of manufacturing defect. The folds locally increase the fiber volume fraction and also introduce resin rich areas. Fatigue tests in fiber direction and transverse to fiber direction are performed at different load ratios under constant amplitude loading. The influence of the defect geometry on damage initiation and progression is investigated at different scales by non-destructive methods before testing, continuous strain measurement and monitoring the damage progression during testing and fractography analysis after final failure. Most of the time, the first damage was observed at the location of the introduced fold for all considered load cases. However, it was also found, that the folds lead to no significant reduction in fatigue life. K EYWORDS . Manufacturing defects; CFRP; Fatigue damage, Fold. Citation: Hörrmann, S., Adumitroaie, A., Schagerl, M., The effect of ply folds as manufacturing defect on the fatigue life of CFRP materials, Frattura ed Integrità Strutturale, 38 (2016) 76-81. Received: 25.05.2016 Accepted: 20.06.2016 Published: 01.10.2016 Copyright: © 2016 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION he high pressure resin transfer molding (HP-RTM) process shows great potential for efficient manufacturing of automotive composite structures in series production. Unidirectional or woven fiber mats are preformed and positioned in the mold, resin is injected and cures in the closed mold in less than 10 min. However, manufacturing defects as in-plane or out-of-plane waviness as well as ply folding along or transverse to fiber direction cannot be avoided, T