Abstract:
The study presented in this thesis investigates the relationship between the experimentally
determined behaviour of Z-pinned laminates under various delamination fracture loading
conditions and their mesostructure Mode I, mode II and mixed mode 1/11 delamination fracture
testing was carned out on Z-Fibre reinforced unidirectional beams of IMS/924 laminates For
the Double Cantilever Beam specimens (DCB) under mode I loading, the crack propagation
resistance of the beam is enhanced with increased pinning density For the range of pin
diameters and pmmng densities used for this study, the load carrying capability has been
improved by up to 5 times and the apparent toughness has been improved by up to 20 times
The most noteworthy example of the effectiveness of ZFibreTM pinning is the stabilisation of
delamination crack propagation under mode II loading conditions in the intrinsically unstable
3pt-ENF configuration
Although the current data analyses, based on LEFM, included in the test protocols for the
calculation of delamination toughness values are invalidated by the presence of the through-the-
thickness reinforcement, they are used here as the best currently available means of normalising
the fracture results However, these data reduction methods do not allow direct quantification of
effects of the different pinning parameters on the crack bridging capability of the through-the-
thickness reinforcement
In order to relate the micromechanics at the pin level with the Mesomechanics of the
delamination fracture specimens, the determination of the traction laws of a single Z-Fibre,
bridging a crack and deformmg under various loading conditions, have been determined
successfully by single pin experiments A finite element approach, utilising these
experimentally determined single pin bridging laws, is presented as a tool to cany out
parametric studies of the effects of pin length, diameter and location on the behaviour of
delaminating beams The good agreement between the simulated and experimental R-curves
demonstrates that the mode I delamination behaviour of DCB specimens is related to the single
pin pullout traction laws
Finally, preliminary studies of the compression after impact behaviour of ZFibreTh reinforced
laminates indicate the existence of a complex relationship between the dramatic enhancement of
the delamination crack propagation resistance of a material and the much lower (up to 50%)
ultimate improvement in its compression after impact performance
