Interlaminar delamination in unidirectional carbon epoxy composites induced by static and fatigue loading
The research is concerned with the interlaminar delamination
problem in unidirectional Carbon Fibre Reinforced Plastic (CFRP)
laminates under static and fatigue loading. Analytical models
backed by experimental techniques are employed to describe the
delamination behaviour in 00 interfaces.
The problem of a semi-infinite elastic plate loaded along its
straight boundary is persued to develop an analytical and realistic
Double Cantilever Beam (DCB) Model which accounts for the end
deflections associated with deformation beyond a crack tip.
Comparisons with the predictions of existing models and with
available experimental data show good agreement. The analysis is
used to formulate the strain energy release rate (SERR) and the
corresponding stress intensity coefficient. This shows excellent
agreement with other results from more elaborate methods. The SERR
is also formulated for a tapered double cantilever beam and this
agrees well with experiment.
DCB type specimens were tested in load control where the SERR is
measured and compared with theory for, 0* CFRP. Other specimens were
tested- in fatigue and the delamination is described for various
maximum loads. A Paris type formula is given for predicting crack
growth in Oý CFRP.
A theoretical analysis is presented for the crack propagation in
a layered fibre reinforced plastic strip in compression, in the
presence-of a blister. Account is taken of a resin rich layer at
the delaminating edge and of an initial deflection* in the blister
geometry. Typical design curves are, produced which show the influence of blister length, applied strain and resin stiffness on
loads required for delamination.
Blistered sandwich specimens were tested in static compression
where debonding characteristics are explained. The loads required
to initiate delamination are found to compare reasonably well with
theory. Similar specimens were tested in constant amplitude fatigue
compression loading and delamination behaviour is illustrated.