Abstract: The aim of this research was to calculate the
mechanical properties of Pd3Rh and PdRh3 ordered alloys. The
molecular dynamics (MD) simulation technique was used to obtain
temperature dependence of the energy, the Yong modulus, the shear
modulus, the bulk modulus, Poisson-s ratio and the elastic stiffness
constants at the isobaric-isothermal (NPT) ensemble in the range of
100-325 K. The interatomic potential energy and force on atoms were
calculated by Quantum Sutton-Chen (Q-SC) many body potential.
Our MD simulation results show the effect of temperature on the
cohesive energy and mechanical properties of Pd3Rh as well as
PdRh3 alloys. Our computed results show good agreement with the
experimental results where they have been available.
Abstract: Electrical discharge machining (EDM) is well
established machining technique mainly used to machine complex
geometries on difficult-to-machine materials and high strength
temperature resistant alloys. In the present research, the objective is
to study the shape of the electrode and establish the application of
liquid nitrogen in reducing distortion of the electrode during
electrical discharge machining of M2 grade high speed steel using
copper electrodes. Study of roundness was performed on the
electrode to observe the shape of the electrode for both conventional
EDM and EDM with cryogenically cooled electrode. Scanning
Electron Microscope (SEM) has been used to study the shape of
electrode tip. The effect of various parameters such as discharge
current and pulse on time has been studied to understand the behavior
of distortion of electrode. It has been concluded that the shape
retention is better in case of liquid nitrogen cooled electrode.
Abstract: Microplasma welding is a less expensive alternative to
laser welding in dental technology. The aim of the study was to
highlight discontinuities present in the microplasma welded joints of
dental base metal alloys by visual analysis. Five base metal alloys
designated for fixed prostheses manufacture were selected for the
experiments. Using these plates, preliminary tests were conducted by
microplasma welding in butt joint configuration, without filler
material, bilaterally and with filler material, proper for each base
metal. Macroscopic visual inspection was performed to assess
carefully the irregularities in the welds. Electron microscopy allowed
detection of discontinuities that are not visible to the eye and
revealing details regarding location, trajectory, morphology and size
of discontinuities. Supplementing visual control with microscopic
analysis allows to detect small discontinuities, which escapes the
macroscopic control and to make a detailed study of the weld.
Abstract: Structured catalysts formed from the growth of
zeolites on substrates is an area of increasing interest due to the
increased efficiency of the catalytic process, and the ability to
provide superior heat transfer and thermal conductivity for both
exothermic and endothermic processes.
However, the generation of structured catalysts represents a
significant challenge when balancing the relationship variables
between materials properties and catalytic performance, with the
Na2O, H2O and Al2O3 gel composition paying a significant role in
this dynamic, thereby affecting the both the type and range of
application.
The structured catalyst films generated as part of this
investigation have been characterised using a range of techniques,
including X-ray diffraction (XRD), Electron microscopy (SEM),
Energy Dispersive X-ray analysis (EDX) and Thermogravimetric
Analysis (TGA), with the transition from oxide-on-alloy wires to
hydrothermally synthesised uniformly zeolite coated surfaces being
demonstrated using both SEM and XRD. The robustness of the
coatings has been ascertained by subjecting these to thermal cycling
(ambient to 550oC), with the results indicating that the synthesis time
and gel compositions have a crucial effect on the quality of zeolite
growth on the FeCrAlloy wires.
Finally, the activity of the structured catalyst was verified by a
series of comparison experiments with standard zeolite Y catalysts in
powdered pelleted forms.
Abstract: In this paper we will develop a sequential life test approach applied to a modified low alloy-high strength steel part used in highway overpasses in Brazil.We will consider two possible underlying sampling distributions: the Normal and theInverse Weibull models. The minimum life will be considered equal to zero. We will use the two underlying models to analyze a fatigue life test situation, comparing the results obtained from both.Since a major chemical component of this low alloy-high strength steel part has been changed, there is little information available about the possible values that the parameters of the corresponding Normal and Inverse Weibull underlying sampling distributions could have. To estimate the shape and the scale parameters of these two sampling models we will use a maximum likelihood approach for censored failure data. We will also develop a truncation mechanism for the Inverse Weibull and Normal models. We will provide rules to truncate a sequential life testing situation making one of the two possible decisions at the moment of truncation; that is, accept or reject the null hypothesis H0. An example will develop the proposed truncated sequential life testing approach for the Inverse Weibull and Normal models.
Abstract: This study demonstrates the feasibility of joining the commercial pure copper plates by friction stir welding (FSW). Microstructure, microhardness and tensile properties in terms of the joint efficiency were found 94.03 % compare to as receive base material (BM). The average hardness at the top was higher than bottom. Hardness of weld zone was higher than the base material. Different microstructure zones were revealed by optical microscopy and scanning electron microscopy. The stirred zone (SZ) exhibited primary two phases namely, recrystallized grains and fine precipitates in matrix of copper.
Abstract: Excessive ductility demand on shorter piers is a
common problem for irregular bridges subjected to strong ground
motion. Various techniques have been developed to reduce the
likelihood of collapse of bridge due to failure of shorter piers. This
paper presents the new approach to improve the seismic behavior of
such bridges using Nitinol shape memory alloys (SMAs).
Superelastic SMAs have the ability to remain elastic under very large
deformation due to martensitic transformation. This unique property
leads to enhanced performance of controlled bridge compared with
the performance of the reference bridge. To evaluate the effectiveness
of the devices, nonlinear time history analysis is performed on a RC
single column bent highway bridge using a suite of representative
ground motions. The results show that this method is very effective in
limiting the ductility demand of shorter pier.
Abstract: An experimental study is presented on the effect
of microstructural change on the Portevin-Le Chatelier effect
behaviour of Al-2.5%Mg alloy. Tensile tests are performed on
the as received and heat treated (at 400 ºC for 16 hours)
samples for a wide range of strain rates. The serrations
observed in the stress-time curve are investigated from
statistical analysis point of view. Microstructures of the
samples are characterized by optical metallography and X-ray
diffraction. It is found that the excess vacancy generated due
to heat treatment leads to decrease in the strain rate sensitivity
and the increase in the number of stress drop occurrences per
unit time during the PLC effect. The microstructural
parameters like domain size, dislocation density have no
appreciable effect on the PLC effect as far as the statistical
behavior of the serrations is considered.
Abstract: Because of high ductility, aluminum alloys, have been widely used as an important base of metal forming industries. But the main week point of these alloys is their low strength so in forming them with conventional methods like deep drawing, hydro forming, etc have been always faced with problems like fracture during of forming process. Because of this, recently using of explosive forming method for forming of these plates has been recommended. In this paper free explosive forming of A2024 aluminum alloy is numerically simulated and during it, explosion wave propagation process is studied. Consequences of this simulation can be effective in prediction of quality of production. These consequences are compared with an experimental test and show the superiority of this method to similar methods like hydro forming and deep drawing.
Abstract: Single crystals of Magnesium alloys such as pure Mg,
Mg-1Zn-0.5Y, Mg-0.1Y, and Mg-0.1Ce alloys were successfully
fabricated in this study by employing the modified Bridgman method.
To determine the exact orientation of crystals, pole figure
measurement using X-ray diffraction were carried out on each single
crystal. Hardness and compression tests were conducted followed by
subsequent recrysatllization annealing. Recrystallization kinetics of
Mg alloy single crystals has been investigated. Fabricated single
crystals were cut into rectangular shaped specimen and solution
treated at 400oC for 24 hrs, and then deformed in compression mode
by 30% reduction. Annealing treatment for recrystallization has been
conducted on these cold-rolled plates at temperatures of 300oC for
various times from 1 to 20 mins. The microstructure observation and
hardness measurement conducted on the recrystallized specimens
revealed that static recrystallization of ternary alloy single crystal was
very slow, while recrystallization behavior of binary alloy single
crystals appeared to be very fast.
Abstract: Aerospace vehicles are subjected to non-uniform
thermal loading that may cause thermal buckling. A study was
conducted on the thermal post-buckling of shape memory alloy
composite plates subjected to the non-uniform tent-like temperature
field. The shape memory alloy wires were embedded within the
laminated composite plates to add recovery stress to the plates. The
non-linear finite element model that considered the recovery stress of
the shape memory alloy and temperature dependent properties of the
shape memory alloy and composite matrix along with its source
codes were developed. It was found that the post-buckling paths of
the shape memory alloy composite plates subjected to various tentlike
temperature fields were stable within the studied temperature
range. The addition of shape memory alloy wires to the composite
plates was found to significantly improve the post-buckling behavior
of laminated composite plates under non-uniform temperature
distribution.
Abstract: to simulate the phenomenon of electronic transport in semiconductors, we try to adapt a numerical method, often and most frequently it’s that of Monte Carlo. In our work, we applied this method in the case of a ternary alloy semiconductor GaInP in its cubic form; The Calculations are made using a non-parabolic effective-mass energy band model. We consider a band of conduction to three valleys (ΓLX), major of the scattering mechanisms are taken into account in this modeling, as the interactions with the acoustic phonons (elastic collisions) and optics (inelastic collisions). The polar optical phonons cause anisotropic collisions, intra-valleys, very probable in the III-V semiconductors. Other optical phonons, no polar, allow transitions inter-valleys. Initially, we present the full results obtained by the simulation of Monte Carlo in GaInP in stationary regime. We consider thereafter the effects related to the application of an electric field varying according to time, we thus study the transient phenomenon which make their appearance in ternary material
Abstract: The tensile properties of Mg-3%Al nanocrystalline
alloys were investigated at different test environment. Bulk
nanocrystalline samples of these alloy was successfully prepared by
mechanical alloying (MA) followed by cold compaction, sintering,
and hot extrusion process. The crystal size of the consolidated milled
sample was calculated by X-Ray line profile analysis. The
deformation mechanism and microstructural characteristic at
different test condition was discussed extensively. At room
temperature, relatively lower value of activation volume (AV) and
higher value of strain rate sensitivity (SRS) suggests that new rate
controlling mechanism accommodating plastic flow in the present
nanocrystalline sample. The deformation behavior and the
microstructural character of the present samples were discussed in
details.
Abstract: A method of collecting composition data and examining structural features of pearlite lamellae and the parent austenite at the growth interface in a 13wt. % manganese steel has been demonstrated with the use of Scanning Transmission Electron Microscopy (STEM). The combination of composition data and the structural features observed at the growth interface show that available theories of pearlite growth cannot explain all the observations.
Abstract: Friction Stir Welding is a solid state welding technique which can be used to produce sound welds between similar and dissimilar materials. Dissimilar welds which include welds between the different series of aluminium alloys, aluminium to magnesium, steel and titanium has been successfully produced by many researchers. This review covers the work conducted in the above mentioned materials and further concludes by showing the need to fully understand the FSW process in order to expand the latter industrially.
Abstract: Thermally insulating ceramic coatings also known as
thermal barrier coatings (TBCs) have been essential technologies to
improve the performance and efficiency of advanced gas turbines in
service at extremely high temperatures. The damage mechanisms of
air-plasma sprayed YSZ thermal barrier coatings (TBC) with various
microstructures were studied by microscopic techniques after thermal
cycling. The typical degradation of plasma TBCs that occurs during
cyclic furnace testing of an YSZ and alumina coating on a Titanium
alloy are analyzed. During the present investigation the effects of
topcoat thickness, bond coat oxidation, thermal cycle lengths and test
temperature are investigated using thermal cycling. These results
were correlated with stresses measured by a spectroscopic technique
in order to understand specific damage mechanism. The failure
mechanism of former bond coats was found to involve fracture
initiation at the thermally grown oxide (TGO) interface and at the
TGO bond coat interface. The failure mechanism of the YZ was
found to involve combination of fracture along the interface between
TGO and bond coat.
Abstract: This paper proposes a Fuzzy Expert System design to
determine the wearing properties of nitrided and non nitrided steel.
The proposed Fuzzy Expert System approach helps the user and the
manufacturer to forecast the wearing properties of nitrided and non
nitrided steel under specified laboratory conditions. Surfaces of the
engineering components are often nitrided for improving wear,
corosion, fatigue specifications. A major property of nitriding
process is reducing distortion and wearing of the metalic alloys. A
Fuzzy Expert System was developed for determining the wearing and
durability properties of nitrided and non nitrided steels that were
tested under different loads and different sliding speeds in the
laboratory conditions.
Abstract: Polymer-like organic thin films were deposited on both
aluminum alloy type 6061 and glass substrates at room temperature by
Plasma Enhanced Chemical Vapor Deposition (PECVD) methodusing
benzene and hexamethyldisiloxane (HMDSO) as precursor materials.
The surface and physical properties of plasma-polymerized organic
thin films were investigated at different r.f. powers. The effects of
benzene/argon ratio on the properties of plasma polymerized benzene
films were also investigated. It is found that using benzene alone
results in a non-coherent and non-adherent powdery deposited
material. The chemical structure and surface properties of the asgrown
plasma polymerized thin films were analyzed on glass
substrates with FTIR and contact angle measurements. FTIR spectra
of benzene deposited film indicated that the benzene rings are
preserved when increasing benzene ratio and/or decreasing r.f.
powers. FTIR spectra of HMDSO deposited films indicated an
increase of the hydrogen concentration and a decrease of the oxygen
concentration with the increase of r.f. power. The contact angle (θ) of
the films prepared from benzene was found to increase by about 43%
as benzene ratio increases from 10% to 20%. θ was then found to
decrease to the original value (51°) when the benzene ratio increases
to 100%. The contact angle, θ, for both benzene and HMDSO
deposited films were found to increase with r.f. power. This signifies
that the plasma polymerized organic films have substantially low
surface energy as the r.f power increases. The corrosion resistance of
aluminum alloy substrate both bare and covered with plasma
polymerized thin films was carried out by potentiodynamic
polarization measurements in standard 3.5 wt. % NaCl solution at
room temperature. The results indicate that the benzene and HMDSO
deposited films are suitable for protection of the aluminum substrate
against corrosion. The changes in the processing parameters seem to
have a strong influence on the film protective ability. Surface
roughness of films deposited on aluminum alloy substrate was
investigated using scanning electron microscopy (SEM). The SEM
images indicate that the surface roughness of benzene deposited films
increase with decreasing the benzene ratio. SEM images of benzene
and HMDSO deposited films indicate that the surface roughness
decreases with increasing r.f. power. Studying the above parameters
indicate that the films produced are suitable for specific practical
applications.
Abstract: The purpose of this research was to analyze and compare the instability of a contact surface between Copper and Nickel an alloy cathode in vacuum, the different ratio of Copper and Copper were conducted at 1%, 2% and 4% by using the cathode spot model. The transient recovery voltage is predicted. The cathode spot region is recognized as the collisionless space charge sheath connected with singly ionized collisional plasma. It was found that the transient voltage is decreased with increasing the percentage of an amount of Nickel in cathode materials.
Abstract: Minimum Quantity Lubrication (MQL) technique
obtained a significant attention in machining processes to reduce
environmental loads caused by usage of conventional cutting fluids.
Recently nanofluids are finding an extensive application in the field
of mechanical engineering because of their superior lubrication and
heat dissipation characteristics. This paper investigates the use of a
nanofluid under MQL mode to improve grinding characteristics of
Ti-6Al-4V alloy. Taguchi-s experimental design technique has been
used in the present investigation and a second order model has been
established to predict grinding forces and surface roughness.
Different concentrations of water based Al2O3 nanofluids were
applied in the grinding operation through MQL setup developed in
house and the results have been compared with those of conventional
coolant and pure water. Experimental results showed that grinding
forces reduced significantly when nano cutting fluid was used even at
low concentration of the nano particles and surface finish has been
found to improve with higher concentration of the nano particles.