Abstract: Nowadays, engineering ceramics have significant
applications in different industries such as; automotive, aerospace,
electrical, electronics and even martial industries due to their
attractive physical and mechanical properties like very high hardness
and strength at elevated temperatures, chemical stability, low friction
and high wear resistance. However, these interesting properties plus
low heat conductivity make their machining processes too hard,
costly and time consuming. Many attempts have been made in order
to make the grinding process of engineering ceramics easier and
many scientists have tried to find proper techniques to economize
ceramics' machining processes. This paper proposes a new diamond
plunge grinding technique using ultrasonic vibration for grinding
Alumina ceramic (Al2O3). For this purpose, a set of laboratory
equipments have been designed and simulated using Finite Element
Method (FEM) and constructed in order to be used in various
measurements. The results obtained have been compared with the
conventional plunge grinding process without ultrasonic vibration
and indicated that the surface roughness and fracture strength
improved and the grinding forces decreased.
Abstract: Chemical detection is still a continuous challenge when
it comes to designing single-walled carbon nanotube (SWCNT)
sensors with high selectivity, especially in complex chemical
environments. A perfect example of such an environment would be in
thermally oxidized soybean oil. At elevated temperatures, oil oxidizes
through a series of chemical reactions which results in the formation of
monoacylglycerols, diacylglycerols, oxidized triacylglycerols, dimers,
trimers, polymers, free fatty acids, ketones, aldehydes, alcohols,
esters, and other minor products. In order to detect the rancidity of
oxidized soybean oil, carbon nanotube chemiresistor sensors have
been coated with polyethylenimine (PEI) to enhance the sensitivity
and selectivity. PEI functionalized SWCNTs are known to have a high
selectivity towards strong electron withdrawing molecules. The
sensors were very responsive to different oil oxidation levels and
furthermore, displayed a rapid recovery in ambient air without the
need of heating or UV exposure.
Abstract: This paper presents the experimental results on effect of applied voltage stress frequency to the occurrence of electrical treeing in 22 kV cross linked polyethylene (XLPE) insulated cable.Hallow disk of XLPE insulating material with thickness 5 mm taken from unused high voltage cable was used as the specimen in this study. Stainless steel needle was inserted gradually into the specimen to give a tip to earth plane electrode separation of 2.50.2 mm at elevated temperature 105-110°C. The specimen was then annealed for 5 minute to minimize any mechanical stress build up around the needle-plane region before it was cooled down to room temperature. Each specimen were subjected to the same applied voltage stress level at 8 kV AC rms, with various frequency, 50, 100, 500, 1000 and 2000 Hz. Initiation time, propagation speed and pattern of electrical treeing were examined in order to study the effect of applied voltage stress frequency. By the experimental results, initial time of visible treeing decreases with increasing in applied voltage frequency. Also, obviously, propagation speed of electrical treeing increases with increasing in applied voltage frequency.Furthermore, two types of electrical treeing, bush-like and branch-like treeing were observed.The experimental results confirmed the effect of voltage stress frequency as well.
Abstract: The present paper reports results of an experimental
program conducted to study performance of fly ash based
geopolymer pastes at elevated temperature. Three series of
geopolymer pastes differing in Na2O content (8.5%, 10% and 11.5%)
were manufactured by activating low calcium fly ash with a mixture
of sodium hydroxide and sodium silicate solution. The paste
specimens were subjected to temperatures as high as 900oC and the
behaviour at elevated temperatures were investigated on the basis of
physical appearance, weight losses, residual strength, shrinkage
measurements and sorptivity tests at different temperatures. Scanning
electron microscopy along with EDX and XRD tests were also
conducted to examine microstructure and mineralogical changes
during the thermal exposure. Specimens which were initially grey
turned reddish accompanied by appearance of small cracks as the
temperature increased to 900oC. Loss of weight was more in
specimens manufactured with highest Na2O content. Geopolymer
paste specimen containing minimum Na2O performed better than
those with higher Na2O content in terms of residual compressive
strength.
Abstract: High strength concrete has been used in situations
where it may be exposed to elevated temperatures. Numerous authors
have shown the significant contribution of polypropylene fiber to the
spalling resistance of high strength concrete.
When cement-based composite that reinforced by polypropylene
fibers heated up to 170 °C, polypropylene fibers readily melt and
volatilize, creating additional porosity and small channels in to the
matrix that cause the poor structure and low strength.
This investigation develops on the mechanical properties of mortar
incorporating polypropylene fibers exposed to high temperature.
Also effects of different pozzolans on strength behaviour of samples
at elevated temperature have been studied.
To reach this purpose, the specimens were produced by partial
replacement of cement with finely ground glass, silica fume and rice
husk ash as high reactive pozzolans. The amount of this replacement
was 10% by weight of cement to find the effects of pozzolans as a
partial replacement of cement on the mechanical properties of
mortars. In this way, lots of mixtures with 0%, 0.5%, 1% and 1.5% of
polypropylene fibers were cast and tested for compressive and
flexural strength, accordance to ASTM standard. After that
specimens being heated to temperatures of 300, 600 °C, respectively,
the mechanical properties of heated samples were tested.
Mechanical tests showed significant reduction in compressive
strength which could be due to polypropylene fiber melting. Also
pozzolans improve the mechanical properties of sampels.