Effect of in-plane fiber waviness defects on the compressive properties of quasi-isotropic thermoplastic composites

R.D.R Sitohang,W.J.B Grouve,L.L Warnet,R Akkerman

doi:10.1016/j.compstruct.2021.114166

Abstract

The influence of in-plane fiber waviness defects on the compressive properties of quasi-isotropic (QI) carbon polyether-ether-ketone (C/PEEK) composites was investigated experimentally. Specimens with localized waviness were manufactured using a stamp forming process resulting into laminates featuring multiple wavy plies, i.e. from one to three wavy 0° plies in a 24-ply QI composite and a range of maximum waviness angle between 23° to 60°. No significant influence of the waviness was found on the global laminate stiffness. Compression tests coupled with high-speed camera monitoring were performed to study the failure process. It was confirmed that the waviness defects act as a trigger for the initiation of damage, predominantly by the kinking mechanism, resulting into an early failure and significantly lower ultimate strength than the baseline when loading in 0° direction. Furthermore, it was found that all specimens with waviness and with the same layup have a similar strength, indicating that the maximum waviness angle within the range studied in this work did not significantly influence the ultimate compressive strength. However, the presence of waviness in multiple plies clearly affected the strength. It was found that the ultimate compressive strength decreased proportionally to the percentage of plies oriented in the loading direction that is wavy.

Highlights

The previous work by the authors of this paper has indicated that this method was able to provide defects representative of the typical waviness parameters found from actual stamp‐formed parts [5]
The effects of in‐plane waviness defects on the compressive properties of QI carbon polyether‐ether‐ketone (C/PEEK) laminates have been studied in this paper
The compression test results showed no significant influence of waviness on the global laminate stiffness

Summary

Introduction

Continuous fiber reinforced thermoplastic composites (TPCs) are increasingly used over recent decades. These materials are becoming more common, especially in the aerospace industry, as they are ideal for lightweight structure applications. There is a lack of quantitative data and predictive tools for the mechanical performance of parts having fiber waviness, for multidirectional TPC materials. In industrial settings, this practically often leads to rejection of the manufactured part due to the uncertainty and possible risk associated with the waviness defects

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