مجله مهندسی ساخت و تولید ایران
سال هفتم شماره 2 (اردیبهشت 1399)

The presence of residual stresses has severe effects in materials resistance to fatigue, corrosion and failure. The presence of local heat during welding leads to the formation of residual stresses. Vibration stress relief is a modern non-destructive method. This method can release the remained stresses without changing the metallurgical properties of the workpiece. In this study, stress relieving was carried out by harmonic vibrations in a welded joint from AISI 1021 steel, which was fabricated by the manual arc welding process in 2G position according to ASME standard. After the experimental evaluation of the resonance frequency of the welded pipe, the harmonic vibration was applied to the pipes. Hardness tests and measurements of residual stresses were done by hole drilling strain gauge method before and after the vibration stress relieving. For stress relaxation, the welded pipes were sinusoidally vibrated at frequency of 27.8 HZ for 40 minutes. The results show a 11.5% reduction in the hardness and 42% of the peripheral residual stress relieving in the central weld line after applying the vibration on the weld joint. The obtained results prove the efficacy of the vibratory stress relief technique in the release of residual stresses in a welded pipe.

In recent years,the addition of the nanoparticles in base oils has been considered in order to improve the energy absorption and viscosity of oils by researchers. In this regard, in this paper, the effects of the addition of metal oxide nanoparticles, including CdO, NiO, Fe3O4, and ZnO with different weight percentages, on the damping ratio and the viscosity of the glycerin as base fluid has been investigated. The choice of this base fluid is due to its application in some lubricants, which can enhance the energy absorption and also improve the friction coefficient in the contact area of the two surfaces. The metal oxide nanoparticles are synthesized by chemically deposited and they are suspended in glycerin by ultrasonic stimulation. After that, viscosity experiments and OMA method are carried on for measuring viscosity and damping ratio, respectively. To reduce the probability of precipitating nanoparticles, mass fraction of nanoparticles include 0.2, 0.4 and 0.6 grams were chosen. Although, the results show that, the viscosity decreasein different nanoparticles with 0.2 gr mass, it enhance with 0.6 gr mass of the ZnO, CdO and Fe3O4 nanoparticles. On the other hand, despite the fact that all of the nanoparticles have enhanced the damping ratio, the results indicate that trend of variations of the NiO and ZnO nanoparticles are positive and CdO and Fe3O4 nanoparticles are negative.

The tube desalination package is one of the most important equipments for supplying water in refineries. The corrosion causes of aluminum- brass alloy tubes in desalination package were studied in this research. For this purpose, chemical analysis of water To identify the composition of water and X-ray diffraction analysis in order to identify deposits layer, which was formed on the tube surface, was performed. Also to investigate the microstructure of the metal and surface layer and identify the type of corrosion, the samples were examined by scanning electron microscopy (SEM). The pitting corrosion of the samples, with and without deposition, were evaluated. For this purpose, cyclic polarization tests were used. Furthermore, the alloy characterization and the results of inspections during construction, and in compliance with the relevant standards were investigated. The results were shown that the pitting corrosion was the main factor of tube failure which was happened under the carbonate layer

In oil and gas pipes, crack is one of the important defects that can lead to the pipelines fractures under high pressure and tension. This usually involves inconvenient and catastrophic events. Therefore, the timely identification of these cracks can prevent horrible human casualties and financial losses. In this research, digital industrial radiography NDT method was used to identify the cracks in the pipes. In many cases, the generated radiographs do not show clearly the defects and radiography images suffer from low contrast because of the photonic scattering of gamma and X-rays. In this research, an image processing method in wavelet domain was implemented. To improve the contrast, the curvelet method is used to make the defect areas more specific. The results show that this method has some superiority to conventional wavelets due to having higher (more emphasized) wavelets than the ordinary wavelets. So it is more capable of defining defect areas, especially in curvature regions. Radiography experts' judgments have been used to evaluate the results. The results of evaluation show that experts confirm the improvement of the contrast and more specific of the defect areas.

Metal-organic frameworks (MOFs) have been used as electrode materials in supercapacitors (SCs) due to their high specific surface area and the suitability of porosity. However, using single-component MOFs in SCs results in poor electrical conductivity, insufficient stability, and poor mechanical properties, and thwart the effect of high capacity and efficient performance. In this paper, to improve the electron transfer rate and utilize the specific surface of MOFs, graphene was combined by copper-MOF via hydrothermal in-situ synthesis. To prevent agglomeration, graphene (0, 2.5, 5, and 10 wt%) was added during the synthesis. To characterize the structure of nanocomposites, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM) analysis were used. Electrochemical tests such as cyclic voltammetry, electrochemical impedance, and repeatability behavior were performed to study the supercapacitor behavior. The electrodes made by graphene and the copper-based MOFs had the specific capacity of 217 and 187 F/g in a 6M KOH electrolyte, respectively, while their composite had the specific capacity of 550 F/g. As a result, the synergic effect in the composite and enhanced electrical conductivity of MOFs resulted in greater availability of porosities and increased total storage capacity.

Since most of properties of Ferritic Stainless Steels (FSS) is dependent on their crystallographic texture, investigation on the evolution of texture of these alloys through metallurgical processes seems important. However, although different studies are focused on this topic, they have usually considered evolution of texture through conventional forming processes such as rolling while evolution of texture of these steels through severe plastic deformation is less studied. Therefore, the aim of this work is to investigate the evolution of texture of FSS 409 through imposition of a recently developed severe plastic deformation process called Tube Channel Pressing (TCP) accompanied by a subsequent annealing. Results show that processing by TCP and a subsequent annealing weakens the initial texture of tube derived from the rolled sheet. In addition, Lankford value in both of the circumferential and longitudinal directions of tube increases after the applied treatment due to arising of new texture component as well as removal of a few of initial texture components.