Abstract: This study presents an inverse analysis for predicting the thermal conductivities and the heat flux of a high-temperature metallurgical reactor simultaneously. Once these thermal parameters are predicted, the time-varying thickness of the protective phase-change bank that covers the inside surface of the brick walls of a metallurgical reactor can be calculated. The enthalpy method is used to solve the melting/solidification process of the protective bank. The inverse model rests on the Levenberg-Marquardt Method (LMM) combined with the Broyden method (BM). A statistical analysis for the thermal parameter estimation is carried out. The effect of the position of the temperature sensors, total number of measurements and measurement noise on the accuracy of inverse predictions is investigated. Recommendations are made concerning the location of temperature sensors.
Abstract: Increasing demands of contemporary applications for high strength and lightweight materials prompted the development of metal-matrix composites (MMCs). After the discovery of carbon nanotubes (CNTs) in 1991 (revealing an excellent set of mechanical properties) became one of the most promising strengthening materials for MMC applications. Additionally, the relatively low density of the nanotubes imparted high specific strengths, making them perfect strengthening material to reinforce MMCs. In the present study, aluminum-multiwalled carbon nanotubes (Al-MWCNTs) composite was prepared in an air induction furnace. The dispersion of the nanotubes in molten aluminum was assisted by inherent string action of induction heating at 790°C. During the fabrication process, multifunctional fluxes were used to avoid oxidation of the nanotubes and molten aluminum. Subsequently, the melt was cast in to a copper mold and cold rolled to 0.5 mm thickness. During metallographic examination using a scanning electron microscope, it was observed that the nanotubes were effectively dispersed in the matrix. The mechanical properties of the composite were significantly increased as compared to pure aluminum specimen i.e. the yield strength from 65 to 115 MPa, the tensile strength from 82 to 125 MPa and hardness from 27 to 30 HV for pure aluminum and Al-CNTs composite, respectively. To recognize the associated strengthening mechanisms in the nanocomposites, three foremost strengthening models i.e. shear lag model, Orowan looping and Hall-Petch have been critically analyzed; experimental data were found to be closely satisfying the shear lag model.
Abstract: In this study, we report calculations of gate capacitance of AlGaN/GaN HEMTs with nextnano device simulation software. We have used a physical gate capacitance model for III-V FETs that incorporates quantum capacitance and centroid capacitance in the channel. These simulations explore various device structures with different values of barrier thickness and channel thickness. A detailed understanding of the impact of gate capacitance in HEMTs will allow us to determine their role in future 10 nm physical gate length node.
Abstract: In this study, the dynamic analysis of viscoelastic plates with variable thickness is examined. The solutions of dynamic response of viscoelastic thin plates with variable thickness have been obtained by using the functional analysis method in the conjunction with the Gâteaux differential. The four-node serendipity element with four degrees of freedom such as deflection, bending, and twisting moments at each node is used. Additionally, boundary condition terms are included in the functional by using a systematic way. In viscoelastic modeling, Three-parameter Kelvin solid model is employed. The solutions obtained in the Laplace-Carson domain are transformed to the real time domain by using MDOP, Dubner & Abate, and Durbin inverse transform techniques. To test the performance of the proposed mixed finite element formulation, numerical examples are treated.
Abstract: In this study, the influence of rolling process parameters such as the work roll cross angle and work roll shifting value on the strip shape and profile of aluminum have been investigated under dry conditions at a speed ratio of 1.3 using Hille 100 experimental mill. The strip profile was found to improve significantly with increase in work roll cross angle from 0o to 1o, with an associated decrease in rolling force. The effect of roll shifting (from 0 to 8mm) was not as significant as the roll cross angle. However, an increase in work roll shifting value achieved a similar decrease in rolling force as that of work roll cross angle. The effect of work roll shifting was also found to be maximum at an optimum roll speed of 0.0986 m/s for the desired thickness. Of all these parameters, the most significant effect of the strip shape profile was observed with variation of work roll cross angle. However, the rolling force can be a significantly reduced by either increasing the the work roll cross angle or work roll shifting.
Abstract: This work studies the effect of thickness on structural
and electrical properties of CuAlS2 thin films grown by two stage
vacuum thermal evaporation technique. CuAlS2 thin films of
thicknesses 50nm, 100nm and 200nm were deposited on suitably
cleaned corning 7059 glass substrate at room temperature (RT). In
the first stage Cu-Al precursors were grown at room temperature by
thermal evaporation and in the second stage Cu-Al precursors were
converted to CuAlS2 thin films by sulfurisation under sulfur
atmosphere at the temperature of 673K. The structural properties of
the films were examined by X-ray diffraction (XRD) technique while
electrical properties of the specimens were studied using four point
probe method. The XRD studies revealed that the films are of
crystalline in nature having tetragonal structure. The variations of the
micro-structural parameters, such as crystallite size (D), dislocation
density ( ), and micro-strain ( ), with film thickness were
investigated. The results showed that the crystallite sizes increase as
the thickness of the film increases. The dislocation density and
micro-strain decreases as the thickness increases. The resistivity ( )
of CuAlS2 film is found to decrease with increase in film thickness,
which is related to the increase of carrier concentration with film
thickness. Thus thicker films exhibit the lowest resistivity and high
carrier concentration, implying these are the most conductive films.
Low electrical resistivity and high carrier concentration are widely
used as the essential components in various optoelectronic devices
such as light-emitting diode and photovoltaic cells.
Abstract: Plate is one of the popular structural elements used in a wide range of industries and structures. They may be subjected to blast loads during explosion events, missile attacks or aircraft attacks. This study is to investigate dynamic responses of the rectangular plate subjected to explosive loads. The effects of material properties and plate thickness on responses of the plate are to be investigated. The compressive pressure is applied to the surface of the plate. Different amounts of thickness in the range from 1mm to 30mm are considered for the plate to evaluate the changes in responses of the plate with respect to plate thickness. Two different properties are considered for the steel. First, the analysis is performed by considering only the elastic-plastic properties for the steel plate. Later on damping is considered to investigate its effects on the responses of the plate. To do analysis, numerical method using a finite element based package ABAQUS is applied. Finally, dynamic responses and graphs showing the relation between maximum displacement of the plate and aim parameters are provided.
Abstract: Polymeric micro-cantilevers (Cs) are rapidly
becoming popular for MEMS applications such as chemo- and biosensing
as well as purely electromechanical applications such as
microrelays. Polymer materials present suitable physical and
chemical properties combined with low-cost mass production. Hence,
micro-cantilevers made of polymers indicate much more
biocompatibility and adaptability of rapid prototyping along with
mechanical properties. This research studies the effects of three
process and one size factors on the filling behaviour in micro cavity,
and the role of each in the replication of micro parts using different
polymer materials i.e. polypropylene (PP) SABIC 56M10 and
acrylonitrile butadiene styrene (ABS) Magnum 8434 . In particular,
the following factors are considered: barrel temperature, mould
temperature, injection speed and the thickness of micro features. The
study revealed that the barrel temperature and the injection speed are
the key factors affecting the flow length of micro features replicated
in PP and ABS. For both materials, an increase of feature sizes
improves the melt flow. However, the melt fill of micro features does
not increase linearly with the increase of their thickness.
Abstract: This study investigates the effects of the lead angle
and chip thickness variation on surface roughness during the
machining of compacted graphite iron using ceramic cutting tools
under dry cutting conditions. Analytical models were developed for
predicting the surface roughness values of the specimens after the
face milling process. Experimental data was collected and imported
to the artificial neural network model. A multilayer perceptron model
was used with the back propagation algorithm employing the input
parameters of lead angle, cutting speed and feed rate in connection
with chip thickness. Furthermore, analysis of variance was employed
to determine the effects of the cutting parameters on surface
roughness. Artificial neural network and regression analysis were
used to predict surface roughness. The values thus predicted were
compared with the collected experimental data, and the
corresponding percentage error was computed. Analysis results
revealed that the lead angle is the dominant factor affecting surface
roughness. Experimental results indicated an improvement in the
surface roughness value with decreasing lead angle value from 88° to
45°.
Abstract: A dip-coating process has been used to form an
asymmetric silica membrane with improved membrane performance
and reproducibility. First, we deposited repeatedly silica on top of a
commercial alumina membrane support to improve its structural
make up. The membrane is further processed under clean room
conditions to avoid dust impurity and subsequent drying in an oven
for high thermal, chemical and physical stability. The resulting
asymmetric membrane exhibits a gradual change in the membrane
layer thickness. Compared to the support, the dual-layer process
improves the gas flow rates. For the scientific applications for natural
gas purification, CO2, CH4 and H2 gas flow rates were. In addition,
the membrane selectively separated hydrogen.
Abstract: The structures obtained with the use of sandwich
technologies combine low weight with high energy absorbing
capacity and load carrying capacity. Hence, there is a growing and
markedly interest in the use of sandwiches with aluminum foam core
because of very good properties such as flexural rigidity and energy
absorption capability. In the current investigation, the static threepoint
bending tests were carried out on the sandwiches with
aluminum foam core and glass fiber reinforced polymer (GFRP)
skins at different values of support span distances aiming the analyses
of their flexural performance. The influence of the core thickness and
the GFRP skin type was reported in terms of peak load and energy
absorption capacity. For this purpose, the skins with two different
types of fabrics which have same thickness value and the aluminum
foam core with two different thicknesses were bonded with a
commercial polyurethane based flexible adhesive in order to combine
the composite sandwich panels. The main results of the bending tests
are: force-displacement curves, peak force values, absorbed energy,
collapse mechanisms and the effect of the support span length and
core thickness. The results of the experimental study showed that the
sandwich with the skins made of S-Glass Woven fabrics and with the
thicker foam core presented higher mechanical values such as load
carrying and energy absorption capacities. The increment of the
support span distance generated the decrease of the mechanical
values for each type of panels, as expected, because of the inverse
proportion between the force and span length. The most common
failure types of the sandwiches are debonding of the lower skin and
the core shear. The obtained results have particular importance for
applications that require lightweight structures with a high capacity
of energy dissipation, such as the transport industry (automotive,
aerospace, shipbuilding and marine industry), where the problems of
collision and crash have increased in the last years.
Abstract: Reflux condensation occurs in vertical channels and tubes when there is an upward core flow of vapour (or gas-vapour mixture) and a downward flow of the liquid film. The understanding of this condensation configuration is crucial in the design of reflux condensers, distillation columns, and in loss-of-coolant safety analyses in nuclear power plant steam generators. The unique feature of this flow is the upward flow of the vapour-gas mixture (or pure vapour) that retards the liquid flow via shear at the liquid-mixture interface. The present model solves the full, elliptic governing equations in both the film and the gas-vapour core flow. The computational mesh is non-orthogonal and adapts dynamically the phase interface, thus produces a sharp and accurate interface. Shear forces and heat and mass transfer at the interface are accounted for fundamentally. This modeling is a big step ahead of current capabilities by removing the limitations of previous reflux condensation models which inherently cannot account for the detailed local balances of shear, mass, and heat transfer at the interface. Discretisation has been done based on finite volume method and co-located variable storage scheme. An in-house computer code was developed to implement the numerical solution scheme. Detailed results are presented for laminar reflux condensation from steam-air mixtures flowing in vertical parallel plate channels. The results include velocity and gas mass fraction profiles, as well as axial variations of film thickness.
Abstract: In rapid industrial development, the demand for
high-strength and lightweight materials have been increased. Thus,
various CFRP (Carbon Fiber Reinforced Plastics) with composite
materials are being used. The design variables of CFRP are its
lamination direction, order and thickness. Thus, the hardness and
strength of CFRP depends much on their design variables. In this
paper, the lamination direction of CFRP was used to produce a
symmetrical ply [0°/0°, -15°/+15°, -30°/+30°, -45°/+45°, -60°/+60°,
-75°/+75° and 90°/90°] and an asymmetrical ply [0°/15°, 0°/30°,
0°/45°, 0°/60° 0°/75° and 0°/90°]. The bending flexure stress of the
CFRP specimen was evaluated through a bending test. Its thermal
property was measured using an infrared camera. The symmetrical
specimen and the asymmetrical specimen were analyzed. The results
showed that the asymmetrical specimen increased the bending loads
according to the increase in the orientation angle; and from 0°, the
symmetrical specimen showed a tendency opposite the asymmetrical
tendency because the tensile force of fiber differs at the vertical
direction of its load. Also, the infrared camera showed that the thermal
property had a trend similar to that of the mechanical properties.
Abstract: Vacuum Insulation Panel (VIP) can achieve very low
thermal conductivity by evacuating its inner space. Heat transfer in the
core materials of highly-evacuated VIP occurs by conduction through
the solid structure and radiation through the pore. The effect of various
scattering modes in combined conduction-radiation in VIP is
investigated through numerical analysis. The discrete ordinates
interpolation method (DOIM) incorporated with the commercial code
FLUENT® is employed. It is found that backward scattering is more
effective in reducing the total heat transfer while isotropic scattering is
almost identical with pure absorbing/emitting case of the same optical
thickness. For a purely scattering medium, the results agrees well with
additive solution with diffusion approximation, while a modified term
is added in the effect of optical thickness to backward scattering is
employed. For other scattering phase functions, it is also confirmed
that backwardly scattering phase function gives a lower effective
thermal conductivity. Thus the materials with backward scattering
properties, with radiation shields are desirable to lower the thermal
conductivity of VIPs.
Abstract: This work presents the result of investigations aimed
at determining the hardness of the welded Chromoly (A 4130) steel
plate of 2” thickness. Multi pass welding for the thick sections was
carried out and analyzed for the Chromoly alloy steel plates. The
study of hardness at the weld metal reveals that there is the presence
of different micro structure products which yields diverse properties.
The welding carried out using GMAW with ER70s-2 electrode.
Single V groove design was selected for the butt joint configuration.
The presence of hydrogen has been suppressed by selecting low
hydrogen electrode. Preheating of the plate prior to welding reduces
the cooling rate which also affects the weld metal microstructure. The
shielding gas composition used in this analysis is 80% Ar-20% CO2.
The experimental analysis gives the detailed study of the hardness of
the material.
Abstract: This paper presents the electromagnetic interference
(EMI) shielding effectiveness of rice husk and carbon nanotubes
(RHCNTs) composites in the X-band region (8.2-12.4 GHz). The
difference weight ratio of carbon nanotubes (CNTs) were mix with
the rice husk. The rectangular waveguide technique was used to
measure the complex permittivity of the RHCNTs composites
materials. The complex permittivity is represented in terms of both
the real and imaginary parts of permittivity in X-band frequency. The
conductivity of RHCNTs shows increasing when the ratio of CNTs
mixture increases. The composites materials were simulated using
Computer Simulation Technology (CST) Microwave Studio
simulation software. The shielding effectiveness of RHCNTs and
pure rice husk was compared. The highest EMI SE of 30 dB is
obtained for RHCNTs composites of 10 wt % CNTs with 10mm
thickness.
Abstract: Recently, there have been a lot of earthquakes in Japan.
It is necessary to promote seismic isolation devices for buildings. The
devices have been hardly diffused in attached houses, because the
devices are very expensive. We should develop a low-cost seismic
isolation device for detached houses. We suggested a new seismic
isolation device which uses a two-layer circular tube as a unit. If
hysteresis is produced in the two-layer circular tube under lateral
compression load, we think that the two-layer circular tube can have
energy absorbing capacity. It is necessary to contact the outer layer
and the inner layer to produce hysteresis. We have previously reported
how the inner layer comes in contact with the outer layer from a
perspective of analysis used mechanics of materials. We have clarified
that the inner layer comes in contact with the outer layer under a lateral
compression load. In this paper, we explored contact area between the
outer layer and the inner layer under a lateral compression load by
using FEA. We think that changing the inner layer’s thickness is
effective in increase the contact area. In order to change the inner
layer’s thickness, we changed the shape of the inner layer. As a result,
the contact area changes depending on the inner layer’s thickness.
Additionally, we experimented to check whether hysteresis occurs in
fact. As a consequence, we can reveal hysteresis in the two-layer
circular tube under the condition.
Abstract: We offer a new technique for research of stability of current sheaths in space plasma taking into account the effect of polarization. At the beginning, the found perturbation of the distribution function is used for calculation of the dielectric permeability tensor, which simulates inhomogeneous medium of a current sheath. Further, we in the usual manner solve the system of Maxwell's equations closed with the material equation. The amplitudes of Fourier perturbations are considered to be exponentially decaying through the current sheath thickness. The dispersion equation follows from the nontrivial solution requirement for perturbations of the electromagnetic field. The resulting dispersion equation allows one to study the temporal and spatial characteristics of instability modes of the current sheath (within the limits of the proposed model) over a wide frequency range, including low frequencies.
Abstract: Tensile specimens of nonflammable AZ91D Mg alloy were fabricated in this study via cold chamber die-casting process. Dimensions of tensile specimens were 25mm in length, 4mm in width, and 0.8 or 3.0mm in thickness. Microstructure observation was conducted before and after tensile tests at room temperature. In the die casting process, various injection distances from 150 to 260mm were employed to obtain optimum process conditions. Distribution of Al12Mg17 phase was the key factor to determine the mechanical properties of die-cast Mg alloy. Specimens with 3mm of thickness showed superior mechanical properties to those with 0.8mm of thickness. Closed networking of Al12Mg17 phase along grain boundary was found to be detrimental to mechanical properties of die-cast Mg alloy.
Abstract: The fatigue crack growth is stochastic because of the fatigue behavior having an uncertainty and a randomness. Therefore, it is necessary to determine the probability distribution of a grown crack size at a specific fatigue crack propagation life for maintenance of structure as well as reliability estimation. The essential purpose of this study is to present the good probability distribution fit for the grown crack size at a specified fatigue life in a rolled magnesium alloy under different specimen thickness conditions. Fatigue crack propagation experiments are carried out in laboratory air under three conditions of specimen thickness using AZ31 to investigate a stochastic crack growth behavior. The goodness-of-fit test for probability distribution of a grown crack size under different specimen thickness conditions is performed by Anderson-Darling test. The effect of a specimen thickness on variability of a grown crack size is also investigated.