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In this paper, the residual stresses due to circumferential arc weld of the thin walled cylinders have been investigated by using finite element method. The cylinders were of aluminum alloy series 5000. The 3D finite element models have been developed in ABAQUS. The thermal-mechanical analysis was considered as uncoupled. The thermal and mechanical material properties have been defined as temperature dependent. The residual stresses were measured by using Hole drilling method. The experimentally measured data have been used to verify the result of finite element model. By using Taguchi method, the effect of eight geometrical, technological and material different factors have been investigated on the maximum residual stresses in the axial and hoop directions. Considering to a number of factors, L12 Taguchi array has been selected. Each factor has been studied in two levels. The result of statistical analyses have shown that increasing the outer diameter, thickness, heat input rate and yield strength in the studied levels caused the axial and hoop maximum residual stresses enhanced. However, the increase of the section number and the interaction between the outer diameter and heat input rate have led to decrease the maximum hoop residual stresses. Also, the yield strength of material was the most effective factor on maximum axial and hoop residual stresses.

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Residual stresses and distortion are of the main disadvantages of welding process which determining the amount and distribution of them have great importance in the design of structures, especially in the space industry. In this study, a finite element method is used to analyze the thermo- mechanical behavior of a spherical shell due to TIG welding. The spherical shell is made of titanium alloy (Ti-6Al-4V) with 2 mm thickness. The modeling of welding process is based on an uncoupled thermo- mechanical coupling. TIG welding is examined for six cases based on current intensity and welding progress speed setting the voltage on 12 V in all cases. Distribution of temperature and residual stresses caused by TIG welding of the titanium spherical shell have been extracted and compared among the six different cases. The effects of current intensity and welding progress speed on shell distortion and residual stress have been investigated. The results showed that increasing the current intensity and decreasing the welding progress speed have the most effects on longitudinal residual stresses which the amount of this increasing reached to %44 for decreasing the welding progress speed. Welding distortion increases to maximum %132 by increasing current and decreasing welding progress speed.

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Additive manufacturing methods and/or 3D printing have become increasingly popular with a particular emphasis on methods used for metallic materials. Selective Laser Melting (SLM) process is one of the additive manufacturing methods for production of metallic parts. The method was developed in particular to process metal parts that need to be more than 99 percent dense. In this method, according to a predefined pattern, the top surface of the powder layer is scanned by the laser and a local (selective) melt pool is produced in the place of the laser spot which results in a fully dense layer after solidification. In this study, a semi-coupled thermo-mechanical simulation of SLM process is carried out in ABAQUS finite element software. In order to simulate the moving heat flux and update material properties from the powder to the dense solid, the ability of the software for employing user-defined subroutines is employed. Investigation of the residual stress distribution and distortion of a part built using SLM process are the main objectives of this simulation. Results which are presented for two different mechanical boundary conditions show that when the bottom face of the layer is clamped, the top face of the built layer deforms in a concave shape, while the lateral faces of the layer have simply-supported boundary conditions and the bottom face of the layer is free, the part is warped.

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In this study, a non-distractive method of x-ray diffraction (XRD) was used to determine residual stress of rolling mill rolls made of graphite steel (GSH48). This method utilizes the variations of distance between crystal planes as strain. The determination of residual stress was performed samples in different depths before and after conducting ultrasonic peening technology. In UPT process, impacts were exerted on the workpiece ball tool, resulting in the improvement of some mechanical properties such as residual stress by creating work hardening and compression. After the simulation and manufacturing of ultrasonic vibratory tool and then the installation of that on lathe machine, UPT operations were conducted on the prepared samples. Measuring residual stress from surface to 0.5 mm depth was performed before and after the UPT process. After the numerical simulation of the UPT, the distribution of experimental residual stress and numerical simulation was compared that the results suggested the increase of compressive residual stress about 0.4 mm from the surface after the UPT process. The rise of compressive residual stress in the rolling mill rolls leads to the increase of their strength and fatigue life and as a result, their working efficiency is boosted. After the UPT process, the grain size of the surface was calculated from the model of the x-ray diffraction using Viliamson-Hall relation that grain size was obtained 60.2 nm. The refinement of surface structure arises because of displacement arrangement again due to vibration with high frequency and severe plastic deformation after the UPT process.

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In this paper, thermo-mechanical behavior of the welding process was analyzed to determine the effect of edge preparation on the residual stress magnitude and distribution in dissimilar joints. By using a verified finite element model, an efficient user subroutine was developed to consider the effects of phase transformation. In order to verify the model, experimental data for similar and dissimilar joints, obtained by deep hole drilling method, were utilized. Good agreement was observed between the finite element and experimental data. The results indicated that the developed computational method is an effective tool to predict the residual stress of dissimilar weld joints. The present finite element model was developed in a butt-welded pipe to consider the effect of pipe wall-thickness, groove shape and root opening distance. It was observed that the pipe wall-thickness has important influences on the distribution and magnitude of residual stress. Moreover, By increasing the pipe thickness in the dissimilar butt-welded pipes, tensile axial residual stresses on the inner surface of the dissimilar joint decreased on the stainless steel side, but only a small variation was observed on the carbon steel side. compressive axial residual stresses on the inner surface and the tensile axial residual stresses on the outer surface increased by increasing the pipe wall thickness especially on the carbon steel side. Increasing of the weld groove shape and root opening distance lead to higher compressive axial stresses on the inner surface and higher tensile axial stresses on the outer surface, only on the carbon steel side.

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In this paper, the study application of pre-heating on the repair welds in the steel pipes and analysis of thermo-elastic-plastic molding of this process was investigated using finite element method. In order to verify the model, experimental data for repair welding of carbon steel pipe, obtained by deep hole drilling method, were utilized. Good agreement was observed between the finite element and experimental data. The results indicated that the developed computational method is an effective tool to predict the residual stress of pipes in the repair welded. The present finite element model was developed in repair welded carbon steel and stainless steel pipes to consider the effect of preheating. It was observed that by increasing the preheating temperature in the repair welded pipes, tensile axial residual stresses on the inner surface and outer surface of the carbon steel and stainless steel pipes decreased 35 and 50 percent respectively, but the compressive axial residual stresses on the outer surface have small variation. Moreover, by increasing the preheating temperature tensile hoop residual stresses on the outer surface on the stainless steel side and tensile hoop residual stresses on the inner surface on the carbon steel side decreased, but only a small variation was observed on the compressive hoop residual stresses. In general, there is no significant effect on the magnitude and distribution of hoop residual stresses on the inner surface of the stainless steel pipe. Also, high preheating temperatures will have wider distribution of axial residual stresses.

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