EFFECTS OF FIBRE MATRIX ADHESION ON CARBON-FIBER-REINFORCED METAL LAMINATES - I - RESIDUAL STRENGTH/

The role of interfacial adhesion between fibre and Matrix on the resid ual strength behaviour of carbon-fibre-reinforced metal laminates (FRM Ls) has been investigated Differences in fibre/matrix adhesion were ac hieved by using treated and untreated carbon fibres in an epoxy resin system. Mechanical characterisation tests were conducted on bulk compo site specimens to determine various properties such as interlaminar sh ear strength (ILSS) and transverse tension strength which clearly illu strate the difference in fibre/matrix interfacial adhesion. Scanning e lectron microscopy confirmed the difference in fracture surfaces, the untreated fibre composites showing interfacial failure while the treat ed fibre composites showed matrix failure. No clear differences were f ound for the mechanical properties such as tensile strength and Young' s modulus of the FRMLs despite the differences in the bulk composite p roperties. A reduction of 7.5% in the apparent value of the ILSS was i dentified for the untreated fibre laminates by both three-point and fi ve-point bend tests. Residual strength and blunt notch tests showed re markable increases in strength for the untreated fibre specimens over the treated ones. Increases of up to 20% and 14% were found for specim ens with a circular hole and saw cut, respectively. The increase in st rength is attributed to the promotion of fibre/matrix splitting and la rge delamination zones in the untreated fibre specimens owing to the w eak fibre/matrix interface. (C) 1998 Elsevier Science Ltd. All rights reserved.