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During fabrication of fiber
reinforced polymer composites the clay is first mixed with epoxy system using
different methods such as mechanical stirring, high shear mixing and
ultrasonication. This matrix is then reinforced with fibers using a variety of
techniques including hand layup, hot pressing and Vacuum Assisted Resin
Transfer Molding (VARTM) 2-8. Other authors like Quaresimin and Varley 7, Subramaniyan
and Sun 8, Bozkurt et al. 9, and Muhammad Zulfi et al. 10 used different
combinations of hand layup and vacuum bagging/hot processing for preparing
glass fiber reinforced clay nanocomposite samples which resulted in superior
properties including improved flexural strength, modulus of elasticity and resistance
to water absorption.

After this the mixture was placed
under L5M-A High Shear Mixer (HSM) to properly disperse the clay particles in
the epoxy matrix. This epoxy nanoclay mixture was then degassed in vacuum oven
for a total of 12 h under different temperature regimes. The IPDA hardener was then
added in 24:100 w/w ratio to the epoxy-clay mixture and hand mixed. More
details about the optimization of the process parameters can be found in the
work by Al-Qadhi et al. 16,17. In
order to manufacture the hybrid GFRE composites, glass fibers were added to the
epoxy-clay mixture using hand layup. Knowing the dimensions of final sample
plates, the fiber volume fraction (Vf) was fixed at 30% for all
samples manufactured in order to isolate the effects of clay addition.

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The drop weight impact tests were
conducted using an instrumented Instron Dynatup 9250G machine fitted with a
hemispherical tup of 12.5 mm diameter. The machine also employed pneumatic
catching mechanism to prevent multiple impacts. The load cell was calibrated
for each test and impacts were performed on an exposed area of 110 _ 110 mm2
while the four sides were in a clamped position. Four energy levels, i.e 10,
20, 35 and 50 J were selected, based on the damage types, while the
concentration of nanoclays dispersed were 0%, 1.5% and 3%. A total of four
samples were tested for each combination. The extent of damage was judged
according to ASTM-D7136M by employing the back-lighting technique. The data
obtained from these tests included load, energy, and deflection as a function
of time. This transient response data was used to generate the load and energy
versus time plots for different impact energies which were then superimposed
for comparison. Specific parameters like peak load and deflection at peak load
were extracted from the aforementioned plots and tabulated.

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