10.1098/rspa.2000.0774 Modelling the stress-transfer efficiency of carbon–epoxy interfaces By A. Paipetis 1 † and C. Galiotis 1,2 1 Department of Materials, Queen Mary and Westfield College, University of London, Mile End Road, London E1 4NS, UK 2 Institute of Chemical Engineering and High Temperature Processes, Foundation for Research and Technology-Hellas, Stadiou Street, Platani, PO Box 1414, GR-265 00 Patras, Greece Received 28 March 2000; revised 6 September 2000; accepted 19 December 2000 This study involved the investigation of the micromechanics of reinforcement of model carbon fibre–epoxy composites using the technique of remote laser Raman microscopy. The technique allows in situ axial stress monitoring in highly crystalline fibres, such as carbon or Kevlar R . Model composites were subjected to incremental tensile loading, while the stress in the fibre was monitored at each level of applied strain. The stress-transfer regime was studied in the elastic domain using a model single-fibre composite, where a fibre of finite length (i.e. of a length smaller than the coupon gauge length) was embedded along a resin coupon. A shear lag approach was employed to model the stress-transfer efficiency of the interface through the use of the shear-lag parameter β. The stress build-up in the fibre in the presence of energy dissipation mechanisms such as fibre fractures was modelled, and the stress-transfer efficiency was quantified at different levels of applied composite strain. Parallels between the interfacial efficiency of single-fibre systems and practical composites are drawn. Keywords: carbon fibre; epoxy resin; composites; interface; stress transfer; Raman spectroscopy 1. Introduction (a ) The interface The role of the interface lies in transferring stresses between neighbouring fibres through a shear-activated mechanism. This may happen at the locus of a disconti- nuity, such as a fibre fracture, or during off-axis and shear loading. The maximum value of shear stress that the interface can sustain prior to failure is the interfacial shear strength of the system. However, interfacial failure may be defined in a variety of ways. In most of the cases it involves debonding (Netravali et al . 1989), and local matrix yielding (Kelly & Tyson 1965). In general, it can be defined as a progression of damage away from the fibre end that increases with applied strain (Nairn et al . 1996). † Present address: Theoretical and Physical Chemistry Institute, National Hellenic Research Foun- dation, Vass. Konstantinou 48, Athens 11635, Greece. Proc. R. Soc. Lond. A (2001) 457, 1555–1577 1555 c  2001 The Royal Society Downloaded from https://royalsocietypublishing.org/ on 02 February 2023