Page 69 - Polymer-based Nanocomposites for Energy and Environmental Applications

Preparation and properties of nanopolymer advanced composites: A review 47

sheets. Three types of foam cores are prepared; they are neat polyurethane, 0.5%
nanoclay-reinforced polyurethane, and 1% nanoclay-reinforced polyurethane. Face
sheets are made of 1% and 2% nanoclay-infused SC-epoxy reinforced with plain
weave carbon fabric. Samples are then subjected to low-velocity impact loading.
Transient responses of the samples are recorded and analyzed. Damage modes are
studied by sectioning the samples and observed by optical scanning method using
SEM. Nanoclay-infused foam sandwich structures exhibit higher peak loads when
compared with neat foam sandwich structures. Average impact parameters for 1%
face sheet sandwich with neat and nanoclay core samples impacted at 15, 30, and
45 J as given in Table 2.7. Damage analyses showed that nanoclay-infused foams have
smaller damage area than their neat counterparts. Damage parameters for samples
impacted at 30 and 45 J are presented in Table 2.8. They have concluded that, by
adopting nanophased sandwich construction in structures, it is possible to sustain
higher loads and reduce the damage size during impact like events, which resulted
in lowering the reduction in mechanical properties, lowering the cost of repairs, if
warranted.
Edgren et al. [40] have developed an impact damage representation in the carbon
fiber noncrimp fabric-reinforced face sheets for damage tolerance analysis of sand-
wich panels which loaded in compression. They have observed that the hole repre-
sentations of visible impact damage (VID) and, more surprisingly, of the subtle
barely visible impact damage (BVID) are recommended for reliable damage toler-
ance prediction of the compression after impact (CAI) load case for the investigated
panels.
Saha et al. [41] have investigated the effect produced by the addition of nano-TiO 2 ,
nanoclay, CNFs, and multiwalled carbon nanotubes (MWNTs) to the polyurethane
foam core on the debond fracture behavior of S2-glass/SC-15 epoxy face sheet sand-
wich composites. The loadings of nanoparticles are increased in a step of 0.5% by
weight to attain the optimum properties enhancement. Specimens are tested in
mode-I under “tilted sandwich debond” (TSD) configuration. It is observed that the
sandwich composites with nanophased core at 1 wt% loading of nanoclay show the
highest enhancement in debond fracture toughness (about 69%) when compared with
the neat foam core. Among different sized nano-TiO 2 , 5 nm one shows the highest
improvement of about 50%. Summary of the debond fracture toughness results is
shown in Table 2.9.
Hosur et al. [42] have fabricated a sandwich panels with neat and nanophased foam
core and three-layered plain weave carbon fabric/Sc-15 epoxy composite face sheets
and have tested under low-velocity impact test. Test results demonstrate the samples
with nanophased foam sustained higher loads and have lower damage areas when
compared with neat counterparts. Scanning electron microscopy study revealed that
the infusion of nanoclay lead to the stronger cell structure compared with that of neat
foam. Neat foam samples are exhibited in collapsing the cells (see Fig. 2.20A),
whereas cells in the nanoclay foams are breaking under impact loading (see
Fig. 2.20B and C). Response of neat core sandwich samples are relatively elastic,
while that of nanophased core sandwich samples are more brittle.