نشریه مهندسی مکانیک مدرس
سال بیست و چهارم شماره 2 (بهمن 1402)

Today, the industry's need to join dissimilar metals has increased, especially in the automotive and aircraft industries. In this regard, in order to join metals, new methods, called solid state joining, have been used, among which electromagnetic joining is performed with a lower cost and at a higher speed. In this research, firstly, the feasibility of joining copper tubes to composite tubes by electromagnetic method and the quality of the joinit have been studied. Then, the effect of the welding voltage process parameter on the mechanical properties of the strength has been investigated by the ring test. Finally, in order to examine the surface hardness of the welded samples, the Vickers hardness test was performed. The results show that the joining of the copper samples to the composite tubes has been done well. It has been observed that with the increase in voltage, due to the increase in the collision energy of the two tubes, the connection force has increased by about 2 times. In the 8 kV voltage, due to the increase in the impact speed, a more severe plastic deformation has occurred than in other samples which has caused more local deformation of the weld interface and, as a result, an increase in the hardness. The hardness of the interface in this condition was about 8% higher than that of the 5 kV voltage.

Inconel 718 is used in a wide range of industries such as oil and gas, nuclear, aviation, and etc. due to its excellent mechanical properties. The use of additive manufacturing (AM) to manufacture parts is increasing rapidly Due to the dimensional limitations in the manufacturing of parts using the additive manufacturing methods, these parts must be connected to other parts in different applications with the help of conventional methods such as welding. In this research, the thermal analysis of plasma welding of an Inconel 718 sheet made by SLM method using ABAQUS software is discussed. Input heat with Gaussian distribution was entered into the model by DFLUX subprogram with FORTRAN program language. In order to validate the thermal model, the temperature was measured during the welding process using a thermocouple. A relatively good match is observed between the numerical and experimental thermal analysis results. The microstructure of the welded samples was examined with an optical microscope and the microstructure of base metal, fusion zone, and heat affected zone were investigated. The dendritic structure in the welding area and the occurrence of recrystallization in the heat-affected area was evident. The tensile test results showed that the sample without welding has a higher yield and ductility.

Hot corrosion and thermally grown oxide (TGO) formation are destructive factors in thermal barrier coatings (TBCs) that lead to coating failure under operational conditions. In the present study, the hot corrosion behavior and TGO evolution for TBCs whose Bond coat by deposited by atmospheric plasma spraying (APS) and high velocity oxygen fuel (HVOF) thermal spray methods were evaluated. Both types of coatings were subjected to cyclic hot corrosion testing at a temperature of 1100°C in the presence of molten salts of Na2SO4 and V2O5 under identical conditions. Subsequently, their microstructures were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD) images. Additionally, changes in TGO thickness were measured across different cycles using Image J software and SEM images. The results indicate that TBCs deposited using the HVOF method for the bond coat exhibit better performance compared to those deposited using the APS method. The results show that a phase change from tetragonal to monoclinic has occurred for zirconia with the penetration of corrosive salt melt and its reaction with the YSZ layer, and also with the depletion of yttria from the coating structure, YVO4 reaction products have been formed for TBCs. The endurance of hot corrosion cycle of TBCs and the growth behavior of TGO show that the coatings whose interface layer is applied by the HVOF method show better performance than the APS method.

Deficiency of potable water has created many problems for human and human society, Therefore, The production of fresh water from saline water is an important issue. One of the method of production fresh water from saline water is the use of solar stills. This paper is the numerical simulation of the conventional solar stills with setting Rectangular, Triangular, Wavy barriers on the left and right walls inside the solar still. Setting barriers causes a change in the pattern of humid airflow in the solar still that it affect water productivity and convective heat transfer rate. Also, changes in the size and number of barriers cause changes it will be in the result. The continuity, momentum, energy and concentration equations are discretized by finite volume method and the results are presented as flow function and concentration and temperature contours. The simulation results show that setting wavy barriers with A=0.01(m) and N=2 at left wall and A=0.075(m) and N=5 at right wall water productivity and convective heat transfer rate can be increased by about 31% and 31.34%.

In This study, in order to evaluation of ductility and consequently the optimum workability region of novel Ti-3Al-8Mo-7V-3Cr titanium alloy (Ti-3873), the hot tensile tests were performed at a constant strain rate of 0.1 s-1 and the temperature range of 650-850 ℃ . To establish the relationship between microstructural evolution and ductility, the microstructure of the specimen was examined by optical microscopy (OM) and scanning electron microscopy (SEM) after and before hot deformation. The results showed that ductility at the temperatures of 650-750 ℃ , increased from 33% to 54% as a consequence of transformation of α  to β  phases and gradually eliminating the α  phase. The maximum ductility obtained at 850 ℃  with a 71% increase in ductility. Microstructural studies showed the elongated and serrated boundaries confirmed the occurrence of dynamic recovery. Recrystallized grains were also observed at 850 ℃ . Therefore, it can demonstrate that the restoration mechanism of the Ti-3873 alloy during hot tension is dynamic recovery and partial dynamic recrystallization. Finally, according to tension results, the appropriate range of deformation deformation of the Ti-3873 alloy in this study is 800-850 ℃ .

Composite materials are of great interest due to their exceptional strength, hardness-to-density ratio, high corrosion resistance, and low weight. One of the suitable methods for making composite pipes is using the extrusion process. Extrusion is a plastic deformation process that due to the compressive state of stress in extrusion, materials with low plasticity can be formed by this method. This article deals with the experimental-numerical investigation of extrusion, from various methods of forming process. Extrusion is done on a composite tube using aluminum and magnesium alloys. Aluminum is used due to its strength compared to high weight, excellent malleability, and magnesium due to the lightest structural metal, the lowest density among structural materials, machining, welding and casting capabilities, as well as high specific strength. The mentioned process was tested at different extrusion ratio, temperature and speed, and the effect of different process parameters on the properties of the extruded product was investigated. Then the process was simulated in the software and the experimental results obtained from the laboratory work and the numerical results obtained from the simulation were compared and validated with each other and the error percentage between the graphs of the experimental and numerical results was examined.