Abstract:
This thesis describes specific new applications of Z-Fibre
®
pinning and focuses the
attention onto the failure modes of locally reinforced (z-pinned) structures. Design
implications of the use of localised reinforcement on structures, rather than laboratory
coupons, are considered.
Z-pinning reinforcement is applied to cylindrical crash tubes and I-section patch joints
manufactured from woven carbon / epoxy pre-pregs. Z-pinning is shown to improve the
Specific Energy Absorption (SEA) of the crash tubes by up to 76 %, the exact amount
depending on the tube geometry. For the I-section patch joints, an initial increase in
ultimate load carrying capability due to z-pin use is observed and, as the quantity of z-
pins increases, a change in failure mode is induced. Z-pinning is also shown to enhance
the damage tolerance of these. The ability to predict major changes to the structural
response due to use of z-pins, and design for them accordingly, is the next step in the
understanding of the technology.
The design element of this study is contained in the development of a new Finite
Element model using cohesive interface elements. The provision of mode II input data
for this model comes from End Loaded Split (ELS) testing of the woven laminates and
continued development of the Z-shear test. A new analysis for quantifying the crack
sliding displacement, based on the ELS test, is developed. Z-shear testing has shown
that the z-pin ‘mode II’ fracture energy is strongly affected by the amount of mode I
opening of the shear surfaces. Here, new data are obtained for a fully constrained, pure
mode II case. Using this modelling tool, changes in failure mode due to z-pin use can be
predicted. Verification is provided by a new simulation of the I-section patch joint
geometry.
