Pseudo-ductility and reduced notch sensitivity in multi-directional all-carbon/epoxy thin-ply hybrid composites

Gergely Czél,Tamas Rev,Meisam Jalalvand,Mohamad Fotouhi,Marco L Longana,Oliver J Nixon-Pearson,Michael R Wisnom

doi:10.1016/j.compositesa.2017.10.028

Abstract

Un-notched and notched tensile response and damage accumulation of quasi-isotropic carbon/epoxy hybrid laminates made of ultra-high modulus and intermediate modulus carbon fibre/epoxy thin-ply prepregs were studied. It was confirmed that the ply fragmentation demonstrated previously in unidirectional hybrids as a successful pseudo-ductility mechanism can be transferred to multi-directional laminates. Furthermore, reduced notch sensitivity was demonstrated in quasi-isotropic specimens for both open holes and sharp notches as a result of local ply fragmentation around the notch.

Highlights

High performance composites reinforced with carbon and glass fibres exhibit high specific strength and stiffness, which makes them desirable for lightweight applications including spacecraft, aero-structures, motorsports and recreational equipment
High performance pseudo-ductile composites exhibiting a safe, progressive failure process similar to yielding and strain hardening of metals accompanied by detectable damage which can serve as a warning sign well before final failure are of high interest
The authors of this paper have demonstrated pseudo-ductility in both glass-carbon/epoxy [28] and all-carbon/epoxy [29] thinply UD interlayer hybrid composites in tension earlier with high initial modulus, pseudo-yielding, a flat stress plateau and further increase in load towards final failure

Summary

Introduction

High performance composites reinforced with carbon and glass fibres exhibit high specific strength and stiffness, which makes them desirable for lightweight applications including spacecraft, aero-structures, motorsports and recreational equipment. In line with the commonly observed trade-off between strength and ductility [1,2,3,4,5] in metals and other structural materials, stiff and strong composites generally fail suddenly without sufficient warning and residual load bearing capacity. There are two different directions of new material development: There is significant interest in finding tougher and more crack-resistant resins (mainly thermoplastic polymers) which can improve matrix-dominated properties such as delamination resistance. The brittle failure of unidirectional (UD) composites needs to be addressed by focussing on fibre development as the tensile stress-strain response of high performance composites is usually fibre-dominated. The relatively high density of the obtained composites may limit their application in lightweight structures

Objectives

Methods

Results

Conclusion