FEM has been applied to analyse the influence of interlayers on the stress distribution
around cylindrical fibres in an elastic matrix. This being part of a research programme aiming to
enhance the energy absorption characteristics of composites by means of interlayers from materials
exhibiting high ductility under plane strain conditions, e. g. UHMWPE.
The theoretical model is based on the Galerkin weighted residual finite element in conjunction with
a "penalty approach". The advantage of this method for polymer composites is in its ability to cope
very effectively with non-linear systems.
Glass microscope slides were initially used to develop a technique for bonding the ductile
layers on to glass and polyamides respectively, as well as to provide simple verifications of the
applicability of the aforementioned model.
Further experiments were carried out on glass fibres coated with UHMWPE from a xylene
solution, in order to evaluate the applicability of the above technique and of the theoretical model
in actual composite systems.
Although great difficulties were encountered in achieving a well bonded uniform coating
on the glass fibres the results have confirmed the viability of the approach: The impact strength
of compression moulded glass reinforced Nylon plaques, measured with an instrumented falling
weight apparatus was increased up to 400% with a corresponding loss in flexural modulus of only
10-15%. The ductile nature of the interfacial failure between fibres and matrix was also confirmed
by SEM examination of fractured specimens.
Thermal analysis results, especially from DMA indicate that an UHMWPE interlayer
substantially increases the tan 8 of the short fibre composite over a wide temperature range, albeit
with some reduction in modulus. There was good agreement between the flexural modulus results
obtained from DMA tests and those obtained using 3 point bending at room temperature.
Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.