Examinando por Autor "Derazkola, Hamed Aghajani"

Mostrando 1 - 7 de 7
  • Miniatura
    Ítem
    AA5754–Al2O3 nanocomposite prepared by friction stir processing: microstructural evolution and mechanical performance
    (Multidisciplinary Digital Publishing Institute (MDPI), 2024-04) Mohammed, Moustafa M.; Abdullah, Mahmoud E.; Rohim, M. Nafea M.; Kubit, Andrzej; Derazkola, Hamed Aghajani
    The utilization of Al2O3 nanopowder to reinforce AA5754 aluminum alloy through blind holes employing the friction stir processing (FSP) technique to produce an aluminum matrix nanocomposite is explored in this paper. Motivated by the necessity to enhance the strength and ductility of welded joints, the impacts of varying the tool rotational speed (rpm) and blind hole diameter on the microstructure and mechanical properties of the joints are investigated. Experimental characterization techniques including SEM, optical microscopy, microhardness, and tensile tests were employed to analyze the welded joints produced under different processing parameters (tool rotational speeds of 910, 1280, and 1700 rpm, and blind hole diameters of 0, 1, 1.5, and 2 mm). Comparative analyses were conducted against base metal properties and joints without reinforcement powder. It was found that the addition of nanopowder resulted in a decrease in the maximum generated heat during FSP, while also reducing the stir zone size compared to samples without nanopowder. Moreover, enhancements in both the strength and ductility of the joints were observed with the incorporation of Al2O3 nanoparticles. The optimal combination of welding conditions, observed at 1280 rpm rotational speed and 1.5 mm hole diameter, yielded a remarkable ultimate tensile strength of 567 MPa, accompanied by a hardness of 45 HV. These results underscore the potential of nano-Al2O3 reinforcement in significantly improving the mechanical properties of the produced nanocomposite, with implications for advancing the performance of welded structures in various engineering applications
  • Miniatura
    Ítem
    Analysis of super Cr13 stainless-steel internal fracture growth effects during skew mill piercing process
    (Elsevier B.V., 2024-03) Derazkola, Hamed Aghajani; García Gil, Eduardo; Murillo Marrodán, Alberto
    The seamless tube piercing process of super Cr13 martensitic stainless steel is addressed in this paper by comparing industrial piercing tests, laboratory hot tensile tests for material behavior characterization, and finite element simulations. Particular focus is given to the effect of process parameters on internal fracture growth and geometrical homogeneity of the tube. The geometrical non-homogeneities found on industrial pierced tubes are closely related to the change of flow stress of super Cr13 stainless steel during the piercing process. This way, the non-uniform strain rate along the tube's cross-section during piercing affects the fracture growth and, consequently, the thickness homogeneity of the tube, which varies from tip to tail. Due to obtained results, the mean value of pierced tube perimeter is 660 mm, while the mean value of the tube perimeter in the FEM simulation was predicted to be 2 % more (675 mm). The contact temperature of the plug and piercing tube was predicted at 1100 °C, and the mean value of pierced tube diameter in the simulation (210 mm) was 1.5 % more than the mean value of the actual tube (207 mm). The morphology of δ-ferrite affects the origin of primary crack initiation during the piercing process. Short and thick grains of δ-ferrite created at low strain rates that lengthen with increasing strain rate affect fracture sensitivity at the tip of the plug, favoring the non-homogeneity of the material
  • Miniatura
    Ítem
    Effect of warm forming process parameters on 42CrMo4 skew rolled bar mechanical properties and microstructure
    (Springer Science and Business Media Deutschland GmbH, 2024-04) Murillo Marrodán, Alberto; Bulzak, Tomasz; García Gil, Eduardo; Derazkola, Hamed Aghajani; Majerski, Krzysztof; Tomczak, Janusz; Pater, Zbigniew
    Skew rolling is a manufacturing process in which two or three rolls are used to reduce the diameter or modify the shape of a cylindrical workpiece, which is used to manufacture mechanical components such as shafts, rods or balls. Hot conditions are used to overcome limitations related to material ductility, residual stress and machine capacity. In this paper, the warm skew rolling (WSR) process of 42CrMo4 rods is modeled by the finite element method. The effects of forming parameters, namely initial temperature and roll rotational velocity, on the material strain rate, thermal properties, microstructure and hardness were analyzed. Simulation results were validated by experimental process data, while hardness tests and SEM-EBSD microscopy were used to assess mechanical properties and microstructure, respectively. The WSR resulting microstructure is different from the normalized ferritic–pearlitic initial one. The degree of spheroidization (DoS) of cementite increases with temperature. The maximum DoS of 86.5% occurs at the initial temperature of 750 °C, leading to the highest material softening. Rolling from lower temperatures favors grain fragmentation and the achievement of incomplete spheroidization, which, in combination with the highest proportion of high-angle boundaries, contributes to a higher hardness of the rods with respect to those rolled at higher temperatures. The highest reduction in hardness takes place at 750 °C and 30 rpm, leading to 209.4 HV1 (30.7% reduction) and 194.1 HV1 (35.7% reduction) in the near-surface and internal regions, respectively. The driving factor is the transformation of cementite precipitates into a spheroidal form characterized by the greatest degree of dispersion.
  • Miniatura
    Ítem
    Effects of underwater friction stir welding heat generation on residual stress of AA6068-T6 aluminum alloy
    (MDPI, 2022-03-17) Khalaf, Hassanein I. ; Al-Sabur, Raheem ; Abdullah, Mahmoud E. ; Kubit, Andrzej ; Derazkola, Hamed Aghajani
    This article aims to study water-cooling effects on residual stress friction stir welding (FSW) of AA6068-T6 aluminum alloy. For this reason, the FSW and submerged FSW processes are simulated by computational fluid dynamic (CFD) method to study heat generation. The increment hole drilling technique was used to measure the residual stress of welded samples. The simulation results show that materials softening during the FSW process are more than submerged. This phenomenon caused the residual stress of the joint line in the submerged case to be lower than in the regular FSW joint. On the other hand, the results revealed that the maximum residual stresses in both cases are below the yielding strength of the AA6068-T6 aluminum alloy. The results indicated that the residual stress along the longitudinal direction of the joint line is much larger than the transverse direction in both samples.
  • Miniatura
    Ítem
    Investigating the effects of geometrical parameters of re-entrant cells of aluminum 7075-T651 auxetic structures on fatigue life
    (MDPI, 2023-02-10) Ghiasvand, Amir; Fayazi Khanigi, Alireza ; Guerrero, John William Grimaldo; Derazkola, Hamed Aghajani; Tomków, Jacek; Janeczek, Anna; Wolski, Adrian
    In this study, the effects of two geometrical parameters of the re-entrant auxetic cells, namely, internal cell angle ((Formula presented.)) and H/L ratio in which H is the cell height, and L is the cell length, have been studied on the variations of Poisson’s ratio and fatigue life of Aluminum 7075-T6 auxetic structures. Five different values of both the H/L ratio and angle (Formula presented.) were selected. Numerical simulations and fatigue life predictions have been conducted through the use of ABAQUS (version 2022) and MSC Fatigue (version 11.0) software. Results revealed that increases in both the H/L ratio and angle (Formula presented.) improved the average value of Poisson’s ratio. Increasing the H/L ratio from 1 to 1.4 and (Formula presented.) from 50° to 70° increased the values of Poisson’s ratio, respectively, 7.7% and 80%. In all angles, increasing the H/L values decreased the fatigue life of the structures significantly. Furthermore, in all H/L values, an increment in (Formula presented.) caused a reduction in fatigue life. The effects of H/L and (Formula presented.) parameters on fatigue life were dominant in the low cycle fatigue regime. Results also showed that the H/L ratio parameter had greater influence as compared to the (Formula presented.) angle, and the structures with higher auxeticity experienced higher fatigue resistance. It was found that the auxetic property of the structure has a direct relationship with the fatigue resistance of the structure. In all samples, structures with greater auxetic property had higher fatigue resistance.
  • Miniatura
    Ítem
    Microstructural and mechanical analysis of seamless pipes made of superaustenitic stainless steel using cross-roll piercing and elongation
    (Multidisciplinary Digital Publishing Institute (MDPI), 2023-10-14) Murillo Marrodán, Alberto; Gamin, Yury; Kaputkina, Liudmila; García Gil, Eduardo; Aleshchenko, Alexander; Derazkola, Hamed Aghajani ; Pashkov, Alexey; Belokon, Evgeniy
    The cross-roll piercing and elongation (CPE) is a forming process performed at high temperatures and high strain rates. The final product quality is strongly dependent on its microstructure. In this study, a finite element method (FEM) model was developed to better understand plastic deformation effects on microstructure during CPE and to analyze alternative thermo-mechanical processing routes. Specific models were used to simulate dynamic and meta-dynamic recrystallization (DRX and MDRX) for the processing of superaustenitic stainless steel (SASS). In addition, the CPE of SASS was investigated experimentally. The microstructure, mechanical properties, and chemical changes of the final product were assessed using optical microscopy, hardness testing, X-ray diffraction, and SEM-EDS. The results revealed higher temperatures and strain rates in the exterior area of the shell after piercing, and MDRX occurred in the whole thickness. However, an average grain size reduction of 13.9% occurred only in the shell middle and inner diameters. During elongation, the highest values of the strain rate and DRX were observed in the inner region, exhibiting a grain size reduction of 38%. Spread in terms of grain size and grain shape anisotropy was found to be less accentuated for tube samples as compared to the pierced shells.
  • Miniatura
    Ítem
    Room temperature tribological properties of molybdenum-titanium-zirconium (TZM) in metal forming processes
    (Elsevier B.V., 2025-03) Derazkola, Hamed Aghajani; Pelcastre, Leonardo; García Gil, Eduardo; Jimbert Lacha, Pedro José; Hardell, Jens
    This study investigate the effects of temperature on the tribological properties of Titanium-zirconium-molybdenum (TZM). TZM alloy was subjected to sliding contact against AISI 430 steel counterparts at varying temperatures. The results shows, the coefficients of friction (COF) at interface were 0.77, 0.75, 0.71, and 0.69, in the case of 25 °C, 300 °C, 600 °C, and 900 °C test temperatures. The presence of MoO3 and Mo9O26 phases suggested the wear resistance and decreasing COF at high temperature. Temperature is a critical factor influencing material transfer between TZM and AISI 430 steel. The primary TZM wear mechanism at 25 °C involved scratching, surface deformation, and local cracks, while elevated temperatures near 900 °C intensified material adhesion phenomena with a surface shearing effect on the TZM surface after the trotest.