Resumo:
This study is focused on the assessment of the interlaminar fracture toughness in mode II and
vibration mechanical properties of composites reinforced through the thickness with
rectangular z-pinned manufactured by VARTM (Vacuum-assisted resin transfer molding)
process. The influence of z-pinning in the mechanical properties of laminated structures is
carried out and for the specimens with different z-pins sizes and pin areal densities are
manufactured after Design of Experiment (DOE) matrix determination. For the composites
fabricated without a polymeric mold, vibration properties z-pins reinforced composites
demonstrated that the size and density of insertion of z-pins has a direct influence on the
natural frequency of vibration, on the damping, or loss, and the amplitude of vibration. With
the optimization made by the method of response surface (MSR), in a mono-objective
analysis, it was demonstrated that it is possible to obtaining reductions in the maximum
amplitude of forced vibration of 115%, and in an analysis multi objective has been shown that
with a given insertion density and size of z-pins 81% reductions in maximum forced vibration
amplitude and increases of 25% and 11% can be achieved damping factor and natural
frequency of vibration, respectively. For the composites manufactured with polymeric mold,
the fracture toughness in mode II was investigated and the results showed that pinning in
composites improved the fracture resistance for all pinning proposals built. For the NPC
(Non-precracked) step, the highest (GIIc)value achieved was for a 0.50 mm with a 2% pin
density insertion, being 106% higher than the unpinned specimen. For the PC (Precracked)
step, the thicker pins 1.00 mm and 1.10 mm acted again as a positive influence to mitigate the
delamination and achieved elevated values of (GIIc), 77.5% and 78.3% higher than the
unpinned specimen, respectively. The statistical results pointed that for the NPC case, the
increase in density of pins always generates an increase in the fracture toughness and the
contribution of the pin size to increase the fracture toughness. From there, increasing the size
of the pin has little influence in NPC. For PC case, was shown that the pin size increasing
decreases the fracture resistance, except for low pin density. Furthermore, the Artificial
Neural Networks (ANN) trained with part of these experimental data showed excellent
predictive capacity of fracture toughness. The modal responses of the laminates fabricated
with a polymeric mold the experimental results indicated that, in most cases, there was an
increase in the natural frequency and highlights the reduction, from approx. 60% to 70%, in
the amplitude of vibration for all specimens with z-pin reinforcement in comparison to the
unpinned. Furthermore, the experimental data compared the statistical results pointed that z pins had a positive influence increasing and decreasing natural frequency and forced vibration
amplitude, respectively, of z-pinned composites compared to the non-reinforced and the
trained ANN with the experimental data presented a very good agreement with experimental
tests carried out in this investigation for predicting modal response.