Deformation micromechanics of model glass fibre composites

The stress transfer between matrix and fibre in a glass fibre/resin composite is reported. Glass fibres containing a small quantity of samarium fluoride (SmF3) were produced enabling luminescence spectroscopy to be performed. The luminescence band at 648 nm was excited by a laser wavelength of 514 nm and tensile stress on a single glass fibre results in a shift in its absolute position. This shift is shown to be useful in calibrating the point-to-point strain in a fibre embedded in a composite and for deriving the interfacial shear stress (ISS). Strain along single fibres embedded in a model epoxy resin composite subjected to deformation is shown to follow classical composite micromechanics theory. Silane treatment of glass fibres indicates a slightly enhanced adhesion between glass with an epoxy resin, and it is also shown that it is possible to follow the fragmentation process using this technique. The Kelly–Tyson approach of measuring fragment lengths is shown to be inappropriate since the fragments appear to remain fully bonded, at least in the early stages before saturation. This luminescence spectroscopic technique represents a new development in the ability to follow the local mechanics of the interface between glass fibres and transparent resins such as epoxy, and a number of applications are suggested.