---

Multi-pass welding process is one of the most applicative methods of welding in various industries. In this paper, temperature and residual stress distribution due to three pass welding of two plates made of AISI 321 stainless steel having different thicknesses is studied. Welding process consists of three welding passes of two Shielded Metal Arc Welding (SMAW) process and one Gas Tungsten Arc Welding (GTAW) process. First, the benchmark plates are manufactured and welding process is performed. The transient temperature distribution during the welding process is recorded using thermocouples attached to the welding plates. First this process simulated experimentally and temperature distribution during to welding process was measured using thermocouples. Furthermore, the final residual stress distribution after welding process is measured using incremental center hole drilling technique (ICHD). The three pass welding process was then simulated using ABAQUS finite element (FE) code. The finite element model consists of temperature-dependent properties of base metal and weld metal. Furthermore, moving heat source and the element-birth technique is implemented in FE model. Experimentally measured temperature and residual stresses provide an in-depth knowledge insight the complicated welding process. . Comparing between the results shows that the numerical predictions and experimental measurements have good agreement and therefore the FE developed model can be employed in designing and evaluating of welded structures.

---

Creep fracture mechanic parameter, C*, is an essential tool for creep crack growth rate estimation and so remnant life determination of components operating at high temperature. For determining this parameter experimental works, FE methods, and engineering approaches can be utilized. In this paper in order to facilitate FE methods in C* determination for a CT specimen, creep behavior models of Norton and Liu-Murakami were developed and related subroutines were created. Each of the aforementioned models has its own temperature dependent material coefficients which were determined and validated based on creep rupture tests on crack free uniaxial specimens of P91 steel and IN718 super alloy respectively in 650˚C and 620˚C temperature. In this study creep fracture mechanic parameter value of a CT specimen made of P91 steel were derived by application of Norton and Liu-Murakami creep behavior models and results were compared with results of the experimental tests and reference stress engineering approach results. The results indicate that Liu-Murakami creep behavior model most exactly estimates creep fracture mechanics parameter, but yet reference stress engineering approach is the most economical way to determine this parameter.

---

Combined shear extrusion (CSE) is a new severe plastic deformation (SPD) technique to produce bulk ultra-fine grained materials. CSE is obtained by the combination of simple and pure shear extrusion. This technique is based on definitions of pure and simple shear. In the present work, the nonlinear (large) deformation elasticity theory is used for obtaining the shear strain applied to the sample under pure shear extrusion with various angles of distortion. Also plastic deformation characteristics of CSE method were analyzed with finite element analysis using commercial Deform 3D software. Shear strain and effective strain applied to the sample, the load required to carry out the process and the final shape of the cross-sectional area were studied for different angles of distortion. Analytical results and finite element analysis shows by increasing the angles of distortion, shear strain and increased rate of shear strain applied to the sample increased so the effective strain and load required to carry out the process increases. Analysis of finite element and geometry of the die shows that distribution of shear strain and effective strain is inhomogeneously and symmetrical in specimen’s cross section which increases from the center to the corners and by increasing the angles of distortion, distribution of strain becomes more inhomogeneously, also the final shape of the cross-sectional area deforms more.

---

In this paper, by performing heat treatment on IN718 superalloy specimens that are manufactured by additive manufacturing method, the purpose is to investigate the experimental and analytical behavior of stress relaxation. The 3D printed specimens were made by the selective laser melting (SLM) method and after homogenization and solution heat treatment; they were subjected to stress relaxation at the temperature of 650 °C with an initial strain of 1.1% and 2.1% for 8 hours. Due to investigate the effect of strain changes on the stress relaxation, the stress relaxation limit diagram, which is 119.55 and 514.35 MPa for strains of 1.1% and 2.1%, respectively, shows that the stress relaxation limit increases with the increase of the initial strain. Furthermore, by examining the stress relaxation behavior in the experimental specimens, it was found that the amount and slope of the relaxation curve is higher in the specimen with a strain of 2.1%. In the analytical study, the creep constitute equations were also used to investigate the stress relaxation behavior, which by checking the presented comparative curves, by recording the error amount of 2.17% and 3.85% for the strains of 1.1% and 2.1%, respectively, the result of the comparison indicates a good agreement between the analytical results and the experimental curves.

---

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.
 

---

Inconel 718 superalloy is widely used in various industries due to its excellent high-temperature properties. The production of components made from Inconel 718 superalloy through the Selective Laser Melting (SLM) method enables the fabrication of parts with complex geometries. Therefore, improving the mechanical properties of parts produced by SLM using secondary strengthening processes is of great importance. This study investigates the effect of cold pre-strain on the tensile and compressive strength of Inconel 718 superalloy samples produced by SLM. The test specimens were produced by the SLM method and subjected to single-stage (5%-15%-30%) and two-stage (4%-12%-16%) loading. To examine the impact of initial loading on mechanical properties, tensile, compression, and hardness tests were performed, and the microstructure behavior was analyzed using an optical microscope. The results indicate that the yield strength and ultimate tensile strength of the Inconel 718 superalloy in the Y-axis (XY plane) increased by 31.8% and 11.6%, respectively, after applying a 30% initial strain along the Z-axis. The compressive yield strength of Inconel 718 superalloy increased by 79.3% in the Z-direction with a 30% pre-strain. In other words, applying pre-strain along the Z-axis affects the compressive strength in the XZ plane as the principal strain and the tensile strength in the XY plane as the shear strain. Increasing pre-strain to 30% has a minimal effect on the hardness properties of Inconel 718 superalloy. The results from the two-stage loading process indicate an enhancement in strength with the increase in the number of loading stages, attributed to the work-hardening phenomenon