Composite Materials Research Progress

An Experimental and Analytical Study of Unidirectional Carbon Fiber… 133
Manufacturing
Figure 2. TEM micrograph of nano SiC sized particles.
Manufacturing of the Nano-phased Carbon Prepregs
Online solution impregnation and filament winding were used as the method of
manufacturing nano-phased unidirectional carbon prepregs. This method involves four
principle steps: (1) uniform dispersion of nano particles in the resin system; (2) application of
resin reaction mixture onto the reinforcing tows; (3) removal of solvent from the prepregs;
and (4) filament winding.
There are various techniques to disperse nanoparticles in the resin system. Acoustic
cavitation is one of the efficient ways to disperse nano-particles into the virgin materials. In
this case, the ultrasonic power supply (generator) converts 50/60 Hz voltage to a high
frequency electrical energy. This voltage is applied to the piezoelectric crystals within the
converter, where it is changed to small mechnical vibrations. The converter’s longitudinal
vibrations are amplified by the probe (horn) and transmitted to the liquid as ultrasonic waves
consisting of alternate compressions and rarefactions. These pressure fluctuations give rise to
microscopic bubbles (cavities), which expand during the negative pressure excursions, and
implode violently during the positive excursions. Some of these cavities oscillate at a
frequency of the applied field (usually 20 kHz) while the gas content inside these cavities
remains constant. As the bubble collapse, millions of shock waves, eddies and extremes in
pressures and temperatures are generated at the implosion sites. Although this phenomenon
known as cavitation, lasts but a few microseconds, and the amount of energy released by each
individual bubble is minimal, the cumulative amount of energy generated is extremely high.
During the operation, an active cavitation region is created close to the source of the
ultrasound probe and that the ultrasonic processing produces high pitched noise in the form of
harmonics which are above the human audible range, emanating from the container walls and
the fluid surface. The development of cavitation processes in the ultrasonically processed
melt creates favorable conditions for the intensification of various physio-chemical processes.