نشریه مهندسی مکانیک مدرس
سال بیستم شماره 10 (مهر 1399)

Thermal spraying is economical and rapid coating process that creates a rough and clean surface. As a result it can be used for applying the interlayer in transient liquid phase bonding. In the present study, transient liquid phase bonding Al 2024 to Ti-6Al-4V was investigated using brass interlayer, where the interlayer was Cu-Zn foil Cu-Zn thermal spray coat on Al substrate, respectively. The results show that by using thermal spray coat as interlayer, because of the formation of different defects that can be considered as diffusion channels, diffusion potential of Ti and Al becomes higher at the interface. It is concluded that the mechanism of bonding formation involves the diffusion of Cu into Al and Ti base materials and formation of TiAl، TiAl، Cu2 Al and AlCuMg phases and also diffusion of Cu through Al grain boundaries and formation of eutectic phases across the grain boundaries. The formation of these intermetallic phases was confirmed by energy dispersive spectroscopy and X-ray diffraction. Dissolution of the base metals in the joint area and the isothermal solidification process of the thermal sprayed interlayer is more and faster than the foil interlayer. The joint with thermal spray brass coat as interlayer, gives higher shear strength of 25 MPa in comparison with the case of using brass foil as interlayer (14.6 MPa). The decrease in bond strength can be attributed to aggregation and growth of the brittle intermetallics near the joint interface due to lower diffusion potential of Ti and Al in the joint zone.

In the present study, the effect of the inclination angle and geometric parameters of aluminum metal foam on heat transfer free convection is investigated numerically. Heat transfer and fluid flow in metal foam based on volume averaging theory and considering the thermal non-equilibrium condition for the energy equation, and the nonlinear Darcy-Brinkman-Forchheimer equation for the momentum equation is expressed in the porous region, microscopic equations in the pure fluid region and macroscopic equations in the porous region are solved. The finite element method has been used to solve numerical of momentum and energy equations in the porous region and pure fluid. In this study, influence of the inclination angle parameters of the metal foam heat sink, base temperature, and also geometric parameters of foam includes porosity, pore density, and foam height on the thermal performance of metal foam has been investigated. Numerical results show good agreement with the empirical results of otherschr('39') works. Numerical results indicate that at the same temperature, the average Nusselt number of the metal foam heat sink in the horizontal position is 62.6% higher than the horizontal flat plate. Horizontal metal foam has the highest average Nusselt number compared to other angles; For metal foam with a pore density of 5ppi and a porosity of 0.92 in the horizontal position, the average Nusselt number is 22.3% higher than in the vertical position. Besides, in the upward horizontal position, the average Nusselt number is 29.5% higher than in the downward horizontal position.

One of the main objectives of impact mechanics is the design of a structure resistant to explosion by introducing a structure with a special design pattern while maintaining its lightweight conditions. In this study, the plastic deformation and failure pattern of quadrangular metallic plates under localized impulsive loading were investigated due to the lack of experimental, analytical, and numerical results in the field of deformation of multilayer structures under impulsive loading. In this series of experiments, 26 double-layered metallic plates with different layering arrangements of steel-steel and steel-aluminum in different thicknesses were fabricated and designed. To apply the localized impulsive load, a ballistic pendulum system was used without using standoff distance blast tubes. A thick layer of polyester foam was used to prevent explosive debris. Steel plates in different thicknesses of 1, 2, and 2.5mm, and aluminum plates in different thicknesses of 1 and 2mm in 5 different layering configurations were used. In the experimental study, parameters such as impulse, central permanent deflection, and longitudinal strains in x and y directions were measured. The results showed that the use of aluminum plate as a backing layer reduces the explosive performance of the double-layered mixed configurations of steel-aluminum plates under localized impulsive loading.

In the present study, deformation pattern in impact spot welded plates with flat and spherical-nosed projectiles using gas mixture detonation set up has been investigated and compared with numerical simulations. The steel plate with a thickness of 4mm was considered as a base plate and steel plates with 1, 2, and 3mm thicknesses were selected as flyer plates and were under direct contact with flat- and spherical-nosed metallic projectiles with a mass of 650 and 1300 gram, respectively. The average velocity of the projectiles was 600 meters per second. The ABAQUS finite element software was used to investigate the high-velocity impact of projectiles on steel sheets. The Johnson-Cook (J-C) model was utilized to describe the behavior of metals. The deformation of plates during the impact spot welding process has been simulated. Comparing the plate deformation pattern in numerical simulation and experimental results found that the numerical model predicted well the deformation of plates during the projectile impact spot welding process. The stress wave propagation on the flyer plates also was studied numerically. The results show that the waves start from the center and progress to the corners of the plate. The values of the equivalent plastic strain (PEEQ) and shear stress pattern for flyers and target plates have investigated as a measure of the quality of welding.

In this paper, miscible viscous fingering instability in a Darcy and non-Darcy porous media was studied through numerical solution and the formation and growth of finger patterns were discussed. According to the porosity coefficient, the media can be divided into Darcy and non-Darcy categories. Also, flow velocity and fluid used (Newtonian or non-Newtonian) are the factors that limit the use of Darcy’s relation. In this simulation, against most previous studies which had been used the two-phase Darcy’s structural equation to approximate examination of instabilities, a two-dimensional model was used. This model was based on coupling flow equations in porous media (Darcy or Brinkman) and transport of diluted species. The effects of increasing injection rates and viscosity changes were investigated based on Peclet non-dimensional number and viscous ratio on instabilities. Besides, a comparison was done between the results of Darcy’s and Brinkman’s solution at different porosity coefficient and viscosity ratio. Image processing techniques were performed to measure the break through time, perimeter of the interface, fractal dimension and sweep efficiency. With increasing viscosity in Darcy and Brinkman solution, the perimeter of the interface and fractal dimension were increased and more complex fingers generated. As a result, the sweep efficiency of the porous media reduces. In addition, the growth of the media porosity led to sweep efficiency. Finally, it was observed that with increasing injection velocity in Brinkman’s solution, the fingers complexity and perimeter of the interface increased and sweep efficiency decreased.

One of the most important and active body tissues during daily life is the intervertebral disc that not only sustains the applied loads to the spine but also it provides the required flexibility for doing different activities. This tissue as an important factor to carry applied loads to the body is always subjected to possible damages. Hence, due to the improvements in medical sciences in treatment or replacing these damaged tissues, investigating the mechanical behavior of the intervertebral disc and assessing the damage level is a major concern for the researchers. For this purpose, different tests should be carried out but to simulate the behavior of the disc more accurately, it is necessary to ensure that the test conditions are as close as possible to the real ones in the body. Hence, the aim of this research is to develop a set of creep constitutive equations that are based on the experimental investigation of the effect of temperature on the creep behavior of the intervertebral disc. To do this, compressive creep tests were carried out on the goat intervertebral disc tissue and the permeability and aggregate modulus were obtained based on fitting the biphasic constitutive equations with the experimental data. Statistical analyses of the experimental data reveal the significant effect of the temperature on the values of both material parameters and the creep behavior of the intervertebral disc, so that with increasing temperature permeability increases and aggregate modulus decreases or vice versa.

In present study, the experimental investigation and regression analysis of the large plastic deformation of square and rectangular plates subjected to extreme dynamic loading with uniform and localized distribution were discussed. In the experimental section, 5 experiments were conducted on mild steel plates with different thicknesses. To perform the regression analysis and multi-objective optimization, Design-Expert software in conjunction with the response surface methodology were exerted. Subsequently, the effect of parameters such as the thickness of the plate, the impulse of applied load, the mechanical properties of the plate, the loading radius, and the ratio of width to length of the plate on the maximum deflection of quadrangular plates was simultaneously investigated. Two separate analyses based on statistical analysis and ANOVA were performed for each type of uniform and localized loading. The values obtained for the coefficient of determination (R2) of two types of uniform and localized loading showed that the models have a good prediction ability of the experimental results and it can be used to evaluate the plastic deformation of the quadrangular plates. Subsequently, the optimal conditions for each effective parameter including yield stress and width to length ratio were determined with respect to considering the minimum values for central deflection and plate thickness simultaneously. The multi-objective optimization results were compared to the experimental results of the present study.

In this study, the effects of burner nozzle length changes on combustion characteristics of a swirl premixed flame are investigated. Three nozzles with different lengths (2.5, 4.5, and 7cm) have been used. Also, in order to investigate the effect of swirler geometry on the combustion characteristics of flame along with changes in nozzle length, 7 swirlers with different geometries were examined. In the study of flame stability, certain values of the bulk velocity were selected, which in these values the equivalence ratio of the fuel-air mixture was changed to determine the unfavorable flame condition such as blow-off and flame attachment to the nozzle. By determining these limits, the flame stability map was obtained in a range of different swirlers geometries, different burner nozzle lengths, and different flow mass velocities. The results showed that by increasing the swirlers radius ratio, the blow-off limit of swirlers decreases so that by increasing the radius ratio from 0.57 to 0.71, the blow-off limit decreases about 15%, and the stability of the flame is improved. Reducing the length of the nozzle increases the flame resistance against blow-off. The amount of NOx increased with equivalence ratio and the slope of the increase in NOx increased for the swirler with a higher radius ratio and the in a certain equivalence ratio, the amount of NOx of swirler with a radius ratio of 0.57, which is the lowest radius ratio among other swirlers (about 30%).

Nowadays, the efficient use of solar energy for optimal use in the building industry has become one of the concerns of designers and builders. Studies show that by properly designing the exterior walls of the building, the amount of solar energy absorption can be managed for the building. Ahwaz is a tropical city that needs mechanical cooling most of the year. However, it has five cold months, with 3 months of use of heating systems to provide residents with thermal comfort. Therefore, the thrombus wall has been considered in this study. The aim of this study is to investigate and compare the thermal behavior of thrombus walls with different shapes in the sunny (south) walls of corridor spaces in Ahwaz. Research method is a hybrid method that incorporates empirical research strategies, simulation, and case research. On this basis, after experimental observations and field investigations on real samples, a general pattern was obtained and numerical calculations of the simulations were performed with CTF method after validation and reliability with Energy Plus software. In this study, by studying the sunroof wall (south side) of a default corridor space, five general compositions of the thrombus wall with the same conditions have been simulated and evaluated. The results have shown that in order to manage energy absorption, the geometry of the thrombus wall is of special importance and its chess pattern performs better than other models. At the end, some suggestions have been made.

In this paper, sources of micro-vibration in a reaction wheel assemblies (RWA) are analyzed in detail and their effects arising from flywheel unbalance are tested based on the related equations and by using Kistler table in Space Thruster Institute. RWAs that are used in satellites to control their situations are the major sources of instabilities leading to disturbances in the performance of instruments with high pointing precision. Thus, for the purpose of successful satellite missions, it is important to identify, study, and reduce these sources. To align with this goal, flywheel was balanced according to the equations and the requirements of the ECSS European Space Standard before assembling on the Kistler test table. With the step of 1Hz of rotation frequency, force and torque details were obtained and plotted in waterfall diagrams. These led to the verification of values obtained for static and dynamic unbalances on the graphs. The values achieved for the static and dynamic unbalances were 0.1 and 0.2gr.cm2, respectively.

Nowadays, many attempts have been made to replace conventional materials with polymers which have the advantage of having less weight and higher formability. Polymers besides these advantages have some shortcomings. One method to overcome these shortcomings is to strengthen them by adding other materials to polymers. As an example, polymer nanocomposites are made by adding nanoparticles to polymers to enhance their tribological performance. In this paper, an experimental and numerical study on the correlation between temperature rise and the wear rate in the polyethylene (PE) with 10% ZnO nanoparticles has been investigated. A comparison between pure PE and polymer nanocomposite has been made. A 3D finite element model has been developed in Abaqus to study the wear in the contact of pin and the disk. The results predicted by the FE model are compared to the experimental data obtained in this research using the pin on disk test rig. According to the results, a non-linear relation between temperature changes and wear rate has been developed.

In the last decade, the gas mixture detonation forming (GDF) method has been introduced as a novel and alternative method instead of other high-velocity forming (HVF) methods such as explosive method. Due to the lack of research in this field, the present study investigates the free and die forming of circular metallic plates under gas mixture detonation loading. In this series of experiments, steel plates with thicknesses of 1, 2, and 3mm, aluminum plates with a thickness of 3mm, and brass plates with a thickness of 1mm were used. Furthermore, the test specimens were loaded in the impulse range of 4.12 to 54.68N·s. For better comparison, the same areal density condition was considered to compare the results of steel, aluminum, and brass plates under the same loading conditions. Experimental results showed that using a die with an apex angle of 60° leads to the decrease of the maximum permanent deflection by 14.8, 20.2, and 21.4% in 1, 2, and 3mm steel plates, respectively. Under the same loading and areal density conditions, for free forming, the use of aluminum and brass plates lead to increasing the maximum permanent deflection by 19.4 and 13.1% compared to the steel sample, respectively. However, in die forming, these values were 5 and 2%, respectively. Also, the comparison of the results for aluminum and brass plates shows that the using die forming reduces the maximum permanent deflection of the specimen by 12.1 and 10.6%.

Research results performed by researchers have illustrated that applying electric current to a deforming metal can lead to a reduction in the required deformation force and an improvement in the formability. This technique is known as electrically assisted forming and is used in various forming processes. In this paper, the forming of square cups through electrically assisted deep drawing process was investigated experimentally and the effects of process parameters, including current magnitude, pulse frequency, and waveform (sinusoidal and square) on the forming force, thickness distribution, and drawing depth are examined. In this regard, after designing and preparing the test setup and forming square cups, the experimental results obtained were compared to those of the conventional deep drawing tests. The results showed that increasing the current magnitude leads to reducing the maximum thinning and the forming force in the deep drawing process of the formed parts. Furthermore, it was found that at a higher frequency, the deformation force decreases significantly and thickness distribution becomes more uniform. The comparison of the two waveforms of pulses demonstrated that the sinusoidal waveform has a relatively more significant effect on the reduction of the force and thickness distribution and a considerable effect on the drawing depth.

In this study for the first time, changes in the thickness of the fracture cross-section of the inhomogeneous sample (with horizontal weld seam) of the API X65 steel, using drop weight tear test specimen have been investigated experimentally. The fracture surface of the test specimen consisted of three zones of base metal, heat affected zone and weld metal with different microstructure and mechanical properties. The most thickness reduction was in the cleavage fracture area of the notch root. In the base metal zone, thickness changes were constant which indicated the stable crack growth in this area. In both heat affected zones before and after the weld zone, the thickness changed with a constant slope. Due to the high hardness and low fracture energy of the weld zone, the lowest percentage of thickness changes was in this zone. Thickness in the weld zone increased with a constant slope due to the stretching of the weld zone to the end of the crack growth path by the force caused by the change of fracture mode from tensile to shear. Also in the reverse fracture zone, due to the increased in compressive strain caused by impact of the hammer on the sample, the thickness increases with a significant slope and reached the maximum value.

Heat exchangers facilitate the transfer of heat between fluids with different temperatures. Compared with solids, most fluids have lower heat transfer coefficients and as a result, the use of high heat transfer coefficient solid particles as additives can increase the convective heat transfer coefficient of the fluid. In this study, the effect of the addition of nanoparticles to the base fluid (deionized water), application of triangular-cut twisted tapes as well as corrugation of shell and tube type heat exchangers pipes, is investigated on heat transfer values, friction coefficient variations as well as variations in performance evaluation criterion. The effects of addition of 0.7 and 1% magnesium-oxide nanoparticles on heat transfer coefficient improvements is investigated and the results of simultaneous application of magnesium-oxide water nanoparticles, corrugated pipes, and twisted tapes are compared. Comparisons against the basic conditions (deionized water without nanofluid, corrugated pipes or triangular-cut twisted tapes) indicate a 48% increase in thermal performance, a minuscule increase of 6.3% in friction coefficient and a 46% increase in the performance evaluation criterion as a result of the application of %0.7 magnesium-oxide water nanoparticles, use of corrugated pipes and triangular cut twisted tapes on the inner surface of shell and tube heat exchanger piping. Also, the application of 1% magnesium-oxide water nanofluid, and simultaneous use of corrugated pipes and triangular-cut twisted tapes on shell and tube heat exchanger piping inner surface results in a 72% increase in thermal performance, a minuscule increase of 6.9% in friction coefficient and a 70% increase in the performance evaluation criterion.