International Science Index
Parameter Optimization and Thermal Simulation in Laser Joining of Coach Peel Panels of Dissimilar Materials
The quality of laser welded-brazed (LWB) joints were strongly dependent on the main process parameters, therefore the effect of laser power (3.2–4 kW), welding speed (60–80 mm/s) and wire feed rate (70–90 mm/s) on mechanical strength and surface roughness were investigated in this study. The comprehensive optimization process by means of response surface methodology (RSM) and desirability function was used for multi-criteria optimization. The experiments were planned based on Box– Behnken design implementing linear and quadratic polynomial equations for predicting the desired output properties. Finally, validation experiments were conducted on an optimized process condition which exhibited good agreement between the predicted and experimental results. AlSi3Mn1 was selected as the filler material for joining aluminum alloy 6022 and hot-dip galvanized steel in coach peel configuration. The high scanning speed could control the thickness of IMC as thin as 5 µm. The thermal simulations of joining process were conducted by the Finite Element Method (FEM), and results were validated through experimental data. The Fe/Al interfacial thermal history evidenced that the duration of critical temperature range (700–900 °C) in this high scanning speed process was less than 1 s. This short interaction time leads to the formation of reaction-control IMC layer instead of diffusion-control mechanisms.
The Spectral Power Amplification on the Regular Lattices
We show that a simple transformation between the regular lattices (the square, the triangular, and the honeycomb) belonging to the same dimensionality can explain in a natural way the universality of the critical exponents found in phase transitions and critical phenomena. It suffices that the Hamiltonian and the lattice present similar writing forms. In addition, it appears that if a property can be calculated for a given lattice then it can be extrapolated simply to any other lattice belonging to the same dimensionality. In this study, we have restricted ourselves on the spectral power amplification (SPA), we note that the SPA does not have an effect on the critical exponents but does have an effect by the criticality temperature of the lattice; the generalisation to other lattice could be shown according to the containment principle.
Deformation of Metallic Foams with Closed Cell at High Temperatures
The aim of this study is to investigate formability of
Al based closed cell metallic foams at high temperature. The foam
specimens with rectangular section were produced from
AlMg1Si0.6TiH20.8 alloy preform material. Bending and free
bending tests based on gravity effect were applied to foam specimens
at high temperatures. During the tests, the time-angular deformation
relationships with various temperatures were determined.
Deformation types formed in cell walls were investigated by means
of Scanning Electron Microscopy (SEM) and optical microscopy.
Bending deformation about 90° was achieved without any defect at
high temperatures. The importance of a critical temperature and
deformation rate was emphasized in maintaining the deformation.
Significant slip lines on surface of cell walls at tensile zones of
bending specimen were observed. At high strain rates, the microcrack
formation in boundaries of elongated grains was determined.
The Effect of the Crystal Field Interaction on the Critical Temperatures and the Sublattice Magnetizations of a Mixed Spin-3/2 and Spin-5/2 Ferrimagnetic System
The influence of the crystal field interactions on the mixed spin-3/2 and spin-5/2 ferrimagnetic Ising system is considered by using the mean field theory based on Bogoliubov inequality for the Gibbs free energy. The ground-state phase diagram is constructed, the phase diagrams of the second-order critical temperatures are obtained, and the thermal variation of the sublattice magnetizations is investigated in detail. We find some interesting phenomena for the sublattice magnetizations at particular values of the crystal field interactions.
Effect of Co3O4 Nanoparticles Addition on (Bi,Pb)-2223 Superconductor
The effect of nano Co3O4 addition on the
superconducting properties of (Bi, Pb)-2223 system was studied. The
samples were prepared by the acetate coprecipitation method. The
Co3O4 with different sizes (10-30 nm and 30-50 nm) from x=0.00 to
0.05 was added to Bi1.6Pb0.4Sr2Ca2Cu3Oy(Co3O4)x. Phase analysis by
XRD method, microstructural examination by SEM and dc electrical
resistivity by four point probe method were done to characterize the
samples. The X-ray diffraction patterns of all the samples indicated
the majority Bi-2223 phase along with minor Bi-2212 and Bi-2201
phases. The volume fraction was estimated from the intensities of Bi-
2223, Bi-2212 and Bi-2201 phase. The sample with x=0.01 wt% of
the added Co3O4 (10-30 nm size) showed the highest volume fraction
of Bi-2223 phase (72%) and the highest superconducting transition
temperature, Tc (~102 K). The non-added sample showed the highest
Tc(~103 K) compared to added samples with nano Co3O4 (30-50 nm
size) added samples. Both the onset critical temperature Tc(onset)
and zero electrical resistivity temperature Tc(R=0) were in the range
of 103-115 ±1K and 91-103 ±1K respectively for samples with added
Co3O4 (10-30 nm and 30-50 nm).
Study of Effective Moisture Diffusivity of Oak Acorn
The purpose of present work was to study the drying kinetics of whole acorn and its kernel at different drying air temperatures and their effective moisture diffusivity. The results indicated that the drying time of whole acorn was 442, 206 and 188 min at the air temperature of 65, 75 and 85ºC, respectively. At the same temperatures, the drying time of kernel was 131, 56 and 76min. The results showed that the effect of drying air temperature increasing on the drying time reduction could not be significant on acorn drying at all conditions. The effective moisture diffusivity of whole acorn and kernel increased with increasing air temperature from 65 to 75ºC. However more air temperature increasing, led to decreasing this property of acorn kernel. The critical temperature of acorn drying was about 75°C in which acorn kernel had the highest effective moisture diffusivity.
The Effects of Various Boundary Conditions on Thermal Buckling of Functionally Graded Beamwith Piezoelectric Layers Based on Third order Shear Deformation Theory
This article attempts to analyze functionally graded beam thermal buckling along with piezoelectric layers applying based on the third order shearing deformation theory considering various boundary conditions. The beam properties are assumed to vary continuously from the lower surface to the upper surface of the beam. The equilibrium equations are derived using the total potential energy equations, Euler equations, piezoelectric material constitutive equations and third order shear deformation theory assumptions. In order to fulfill such an aim, at first functionally graded beam with piezoelectric layers applying the third order shearing deformation theory along with clamped -clamped boundary conditions are thoroughly analyzed, and then following making sure of the correctness of all the equations, the very same beam is analyzed with piezoelectric layers through simply-simply and simply-clamped boundary conditions. In this article buckling critical temperature for functionally graded beam is derived in two different ways, without piezoelectric layer and with piezoelectric layer and the results are compared together. Finally, all the conclusions obtained will be compared and contrasted with the same samples in the same and distinguished conditions through tables and charts. It would be noteworthy that in this article, the software MAPLE has been applied in order to do the numeral calculations.
Thermal and Mechanical Buckling of Short and Long Functionally Graded Cylindrical Shells Using First Order Shear Deformation Theory
This paper presents the buckling analysis of short and
long functionally graded cylindrical shells under thermal and
mechanical loads. The shell properties are assumed to vary
continuously from the inner surface to the outer surface of the shell.
The equilibrium and stability equations are derived using the total
potential energy equations, Euler equations and first order shear
deformation theory assumptions. The resulting equations are solved
for simply supported boundary conditions. The critical temperature
and pressure loads are calculated for both short and long cylindrical
shells. Comparison studies show the effects of functionally graded
index, loading type and shell geometry on critical buckling loads of
short and long functionally graded cylindrical shells.
The Survey of the Buckling Effect of Laminated Plate under the Thermal Load using Complex Finite Strip Method
This article considers the positional buckling of
composite thick plates under thermal loading . For this purpose , the
complex finite strip method is used . In analysis of complex finite
strip, harmonic complex function in longitudinal direction , cubic
functions in transversal direction and parabola distribution of
transverse shear strain in thickness of thick plate based on higherorder
shear deformation theory are used . In given examples , the
effect of angles of stratification , number of layers , dimensions ratio
and length – to – thick ratio across critical temperature are
Vibration Damping of High-Chromium Ferromagnetic Steel
The aim of the present work is to study the effect of annealing on the vibration damping capacity of high-chromium (16%) ferromagnetic steel. The alloys were prepared from raw materials of 99.9% purity melted in a high frequency induction furnace under high vacuum. The samples were heat-treated in vacuum at various temperatures (800 to 1200ºC) for 1 hour followed by slow cooling (120ºC/h). The inverted torsional pendulum method was used to evaluate the vibration damping capacity. The results indicated that the vibration damping capacity of the alloys is influenced by annealing and there exists a critical annealing temperature after 1000ºC. The damping capacity increases quickly below the critical temperature since the magnetic domains move more easily.
Impact of Viscous and Heat Relaxation Loss on the Critical Temperature Gradients of Thermoacoustic Stacks
A stack with a small critical temperature gradient is
desirable for a standing wave thermoacoustic engine to obtain a low
onset temperature difference (the minimum temperature difference to
start engine-s self-oscillation). The viscous and heat relaxation loss in
the stack determines the critical temperature gradient. In this work, a
dimensionless critical temperature gradient factor is obtained based
on the linear thermoacoustic theory. It is indicated that the
impedance determines the proportion between the viscous loss, heat
relaxation losses and the power production from the heat energy. It
reveals the effects of the channel dimensions, geometrical
configuration and the local acoustic impedance on the critical
temperature gradient in stacks. The numerical analysis shows that
there exists a possible optimum combination of these parameters
which leads to the lowest critical temperature gradient. Furthermore,
several different geometries have been tested and compared