پایگاه تخصصی نساجی و پوشاک
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-structured sandwich composites response to low-velocity impact Antonio F.
, 
, , Maria Gabriela R.
This paper investigates the influence of exfoliated 
nano-structures on sandwich composites under impact loadings. A set of sandwich composites plates made of fiberglass/nano-modified
epoxy face sheets and polystyrene foams was prepared. The core was
25 mm thick and the face sheets were made of eight layers of woven
fabric glass fibers and nano-modified epoxy (≈0.8 mm of thickness). The epoxy system was bisphenol A resin and an amine hardener. The fiber
volume fraction used was around 65%, while the nanoclay content varied
from 0 wt.% to 10 wt.%. The nanoclay used was Cloisite 30B from
Southern Clay. The sandwich panels were submitted to low-velocity
impact tests with energies from 5 J to 75 J. Two sets of experiments
were performed, i.e. high velocity + low mass and low velocity + high
mass. Damage caused by the two groups of experiments and peak forces
measured were dissimilar. The results show that the addition of 5 wt.%
of nanoclay lead to a more efficient energy absorption. The failure
modes were also analyzed, and they seems to be affected by the nanoclay
addition to face sheets.
Keywords: Sandwich composites; Nanocomposites; Low-velocity impact; Nanoclay; Mechanical properties; Modeling
- to meter-scale building Danijel, , Martin
The construction industry will have to find new ways of building to accomplish radical reductions of pollution and waste. Nano
and biotechnology along with information technology have the potential
to constitute a new building paradigm. The paper describes the concept
of nano-
to meter-scale building, which is based on this potential. The concept
is not focused on the application of nanomaterials like nanosilica or
carbon nanotubes, but on a new way of building, which unfolds from the nano into the meter range. It is based on bionanorobots, producing building materials using carbon extracted from CO2
in the air. Criteria and requirements regarding relevant technologies
are defined and compared to the current research in the fields of
bioengineering, nanorobotics, and characteristics and production of
carbon nanotubes. The paper also presents a concept of a new building
technology that would enable control and monitoring of construction at
the nano
level, as well as requirements regarding design methods and tools
including the building information model that will become the only
human input to the automated nano- to meter-scale building process. The paper concludes with suggestions for further research and development.
-clay on physico-mechanical properties of cement mortar M.S., a, , S.H.
In this work, several nanomaterials have been used in cementitious matrices: multi wall carbon nanotubes (MWCNTs) and nano-clays. The physico-mechanical behavior of these nanomaterials and ordinary Portland cement (OPC) was studied. The nano-clay used in this investigation was nano-kaolin. The metakaolin was prepared by thermal activation of nano-kaolin
clay at 750 °C for 2 h. The organic ammonium chloride was used to aid
in the exfoliation of the clay platelets. The blended cement used in
this investigation consists of ordinary Portland cement, carbon
nanotubes and exfoliated nano metakaolin. The OPC was substituted by 6 wt.% of cement by nano
metakaolin (NMK) and the carbon nanotube was added by ratios of 0.005,
0.02, 0.05 and 0.1 wt.% of cement. The blended cement: sand ratio used
in this investigation was 1:2 wt.%. The blended cement mortar was
prepared using water/binder ratio of 0.5 wt.% of cement. The fresh
mortar pastes were first cured at 100% relative humidity for 24 h and
then cured in water for 28 days. Compressive strength, phase
composition and microstructure of blended cement were investigated. The
results showed that, the replacement of OPC by 6 wt.% NMK increases the
compressive strength of blended mortar by 18% compared to control mix
and the combination of 6 wt.% NMK and 0.02 wt.% CNTs increased the
compressive strength by 29% than control.
Keywords: Carbon nanotube; Nano-clay; Cement mortar; Thermal analysis; Compressive strength; Microstructure
-reinforced epoxies S.A., a, , J.M.
In this paper, an atomistic-based
representative volume element (RVE) is developed to characterize the
behavior of carbon nanotube (CNT) reinforced amorphous epoxies. The RVE
consists of the carbon nanotube, the surrounding epoxy matrix, and the
CNT/epoxy interface. An atomistic-based continuum representation is
adopted throughout all the components of the RVE. By equating the
associated strain energies under identical loading conditions, we were
able to homogenize the RVE into a representative fiber.
The homogenized RVE was then employed in a micromechanical analysis to
predict the effective properties of the newly developed CNT-reinforced
amorphous epoxy. Numerical examples show that the effect of volume
fraction, orientation, and aspect ratio of the continuous fibres
on the properties of the CNT-reinforced epoxy adhesives can be
significant. These results have a direct bearing on the design and
development of nano-tailored adhesives for use in structural adhesive bonds.
Keywords: Atomistic-based continuum; Nano-reinforced epoxies; Representative volume element
for centuries. In 5000 BC, our ancestors used natural fibers such as wool, cotton silk and animal fur for clothing. Mass production of fibers dates back to the early stages of the industrial revolution. The first man-made fiber
– viscose – was presented in 1889 at the World Exhibition in Paris.
Developments in the polymer and chemical industries – as well as in
electronics and mechanics – have led to the introduction of new types
of man-made fibers, especially the first synthetic fibers, such as nylon, polypropylene and polyester. The needs and further progress allowed the production of high functionality fibers (antistatic, flame resistant, etc.) and high performance fibers (carbon fibers in 1960 from viscose and aramid fibers in 1965) that showed high strength, a high modulus and great heat resistance. These fibers
are used not only in clothing but also in hygienic products, in medical
and automotive applications, in geo-textiles and in other applications.Traditional methods for polymer fiber
production include melt spinning, dry spinning, wet spinning and
gel-state spinning. These methods rely on mechanical forces to produce fibers
by extruding a polymer melt or solution through a spinneret and
subsequently drawing the resulting filaments as they solidify or
coagulate. These methods allow the production of fiber diameters typically in the range of 5 to 500 microns. At variance, electrospinning technology allows the production of fibers of much smaller dimensions. The fibers are produced by using an electrostatic field [1].
Electrospinning is a fiber-spinning technology used to produce long, three-dimensional, ultra-fine fibers
with diameters in the range of a few nanometers to a few microns (more
typically 100 nm to 1 micron) and lengths up to kilometers (Fig. 16-1). When used in products, the unique properties of nano-fibers
are utilized, such as extraordinarily high surface area per unit mass,
very high porosity, tunable pore size, tunable surface properties,
layer thinness, high permeability, low basic weight, ability to retain
electrostatic charges and cost effectiveness, among others [2].