Examinando por Autor "Aghajani Derazkola, Hamed"
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Ítem Effect of pin shape on thermal history of aluminum-steel friction stir welded joint: computational fluid dynamic modeling and validation(MDPI, 2021-12-01) Bokov, Dmitry; Jawad, Mohammed Abed; Suksatan, Wanich; Abdullah, Mahmoud E. ; Świerczyńska, Aleksandra ; Fydrych, Dariusz; Aghajani Derazkola, HamedThis article studied the effects of pin angle on heat generation and temperature distribution during friction stir welding (FSW) of AA1100 aluminum alloy and St-14 low carbon steel. A validated computational fluid dynamics (CFD) model was implemented to simulate the FSW process. Scanning electron microscopy (SEM) was employed in order to investigate internal materials’ flow. Simulation results revealed that the mechanical work on the joint line increased with the pin angle and larger stir zone forms. The simulation results show that in the angled pin tool, more than 26% of the total heat is produced by the pin. Meanwhile, in other cases, the total heat produced by the pin was near 15% of the total generated heat. The thermo-mechanical cycle in the steel zone increased, and consequently, mechanical interlock between base metals increased. The simulation output demonstrated that the frictional heat generation with a tool without a pin angle is higher than an angled pin. The calculation result also shows that the maximum heat was generated on the steel side.Ítem Effects of FSW tool plunge depth on properties of an Al-Mg-Si alloy t-joint: thermomechanical modeling and experimental evaluation(MDPI AG, 2021-08-02) Memon, Shabbir; Fydrych, Dariusz; Conde Fernández, Aintzane; Aghajani Derazkola, Hamed ; Aghajani Derazkola, HesamoddinOne of the main challenging issues in friction stir welding (FSW) of stiffened structures is maximizing skin and flange mixing. Among the various parameters in FSW that can affect the quality of mixing between skin and flange is tool plunge depth (TPD). In this research, the effects of TPD during FSW of an Al-Mg-Si alloy T-joint are investigated. The computational fluid dynamics (CFD) method can help understand TPD effects on FSW of the T-joint structure. For this reason, the CFD method is employed in the simulation of heat generation, heat distribution, material flow, and defect formation during welding processes at various TPD. CFD is a powerful method that can simu-late phenomena during the mixing of flange and skin that are hard to assess experimentally. For the evaluation of FSW joints, macrostructure visualization is carried out. Simulation results showed that at higher TPD, more frictional heat is generated and causes the formation of a bigger stir zone. The temperature distribution is antisymmetric to the welding line, and the concentration of heat on the advancing side (AS) is more than the retreating side (RS). Simulation results from viscosity changes and material velocity study on the stir zone indicated that the possibility of the formation of a tunnel defect on the skin–flange interface at the RS is very high. Material flow and defect formation are very sensitive to TPD. Low TPD creates internal defects with incomplete mixing of skin and flange, and high TPD forms surface flash. Higher TPD increases frictional heat and axial force that diminish the mixing of skin and flange in this joint. The optimum TPD was selected due to the best materials flow and final mechanical properties of joints.Ítem The effects of pin profile on HDPE thermomechanical phenomena during FSW(MDPI, 2022-10-31) Khalaf, Hassanein I. ; Al-Sabur, Raheem; Demiral, Murat; Tomków, Jacek; Łabanowski, Jerzy ; Abdullah, Mahmoud E. ; Aghajani Derazkola, HamedFriction stir welding (FSW) of polymeric materials has recently attracted significant attention. Herein, we present the effect of the tool pin profile on the FSW of high-density polyethylene (HDPE) joints through joint experimental analysis and thermomechanical simulations. For analysis of pin profile effects on the thermomechanical properties of HDPE joints, frustum (FPT), cubic (CPT), and triangular (TPT) pin shapes were selected in this study. This research investigated the heat generation of the parts of the different tools as well as heat flux (internal and surface). The results revealed that the heat generation in pins with more edges (cubic (96 °C) and triangular (94 °C)) was greater than in pins with a smooth shape (frustum (91 °C)). The higher heat generation caused the heat flux on the surface of the HDPE from the cubic pin profile to be greater than for other joints. Due to the properties of HDPE, higher heat generation caused higher material velocity in the stirring zone, where the velocity of the materials in TPT, CPT, and FPT pins were 0.41 m/s, 0.42 m/s, and 0.4 m/s, respectively. The simulation results show sharp-edged pins, such as triangular and cubic, lead to over-stirring action and internal voids formed along the joint line. Furthermore, the simulation results indicated that the size of the stirred zones (SZs) of the FPT, TPT, and CPT samples were 17 mm2, 19 mm2, and 21 mm2, respectively, which is around three times the corresponding values in the HAZ.Ítem Effects of rapid cooling on properties of aluminum-steel friction stir welded joint(MDPI AG, 2021-02-02) Aghajani Derazkola, Hamed ; García Gil, Eduardo ; Eyvazian, Arameh; Aberoumand, MohammadIn this study, dissimilar sheets including AA3003 aluminum and A441 AISI steel were welded via cooling-assisted friction stir welding (FSW). Three different cooling mediums including forced CO2, forced water, and forced air were employed, and a non-cooled sample was processed to compare the cooling-assisted condition with the traditional FSW condition. The highest cooling rate belongs to CO2 and the lowest cooling rate belongs to the non-cooled sample as FSW. The best macrograph without any segregation at interface belongs to the water-cooled sample and the poorest joint with notable segregation belongs to the CO2 cooling FSW sample. The CO2 cooling FSW sample exhibits the smallest grain size due to the suppression of grain growth during dynamic recrystallization (DRX). The intermetallic compound (IMC) thickening was suppressed by a higher cooling rate in CO2 cooling sample and just Al-rich phase was formed in this joint. The lowest cooling rate in the FSW sample exhibits formation of the Fe rich phase. The IMC layers were thicker at the top of the weld due to closeness with the heat generation source. The water cooling sample exhibits the highest tensile strength due to proper mechanical bonding simultaneously with optimum IMC thickness to provide appropriate metallurgical bonding. Fractography observation indicates that there is a semi-ductile fracture in the water cooling sample and CO2 cooling sample exhibits more brittle fracture. Hardness evaluation reveals that the higher the cooling rate formed, the higher the hardness in stir zone, and hardness changes in the aluminum side were higher than the steel side.Ítem Effects of tool–workpiece interfaces friction coefficient on power and energy consumption during the piercing phase of seamless tube production(Elsevier Editora Ltda, 2022-06-17) Aghajani Derazkola, Hamed; García Gil, Eduardo; Murillo Marrodán, AlbertoThis research analyzes the impact of various friction conditions at the interface of the tube piercing machine tools and Super Cr13 steel workpiece. For this reason, the three-dimensional finite element method (FEM) is employed in the simulation of the tube piercing process. The friction conditions are simulated considering Tresca, Viscoplastic, IFUM and Neumaier models which have been implemented at the Rollers-Billet (RF), Plug–Billet (PF), and Diescher–Billet (DF) interfaces. After testing their performance, Viscoplastic is selected for RF interface, and Tresca for PF and DF interfaces, respectively. Additionally, a friction coefficient range between 0.01 and 0.6 is used for RF, 0.06–0.15 for PF, and 0.1–0.3 for DF. The relation between normal stress, strain, temperature, and quality of pierced tubes is discussed, as well as the connection between the friction coefficient and the energy consumption. The FEM results are validated by actual piercing process data provided by Industry. The results show that the normal stress on billet during piercing increases by increasing friction on RF interface. With increasing friction in PF, both friction power and plastic power increase, while increasing friction in RF lead to a friction and plastic power decrease. According to the results, the minimum energy consumption is recorded at RF = 0.5, PF = 0.06, and DF = 0.1.Ítem Review on dynamic recrystallization of martensitic stainless steels during hot deformation: part I—experimental study(MDPI AG, 2021-04-01) Aghajani Derazkola, Hamed ; García Gil, Eduardo; Murillo Marrodán, Alberto; Méresse, DamienThe evolution of the microstructure changes during hot deformation of high-chromium content of stainless steels (martensitic stainless steels) is reviewed. The microstructural changes taking place under high-temperature conditions and the associated mechanical behaviors are presented. During the continuous dynamic recrystallization (cDRX), the new grains nucleate and growth in materials with high stacking fault energies (SFE). On the other hand, new ultrafine grains could be produced in stainless steel material irrespective of the SFE employing high deformation and temperatures. The gradual transformation results from the dislocation of sub-boundaries created at low strains into ultrafine grains with high angle boundaries at large strains. There is limited information about flow stress and monitoring microstructure changes during the hot forming of martensitic stainless steels. For this reason, continuous dynamic recrystallization (cDRX) is still not entirely understood for these types of metals. Recent studies of the deformation behavior of martensitic stainless steels under thermomechanical conditions investigated the relationship between the microstructural changes and mechanical properties. In this review, grain formation under thermomechanical conditions and dynamic recrystallization behavior of this type of steel during the deformation phase is discussed.Ítem Tribological behaviour of DIN 1.2740 hot working tool steel during mandrel mill stretching process(Elsevier Ltd, 2025-02) Aghajani Derazkola, Hamed; Fauconnier, Dieter; Kalácska, Ádám; García Gil, Eduardo; Murillo Marrodán, Alberto; De Baets, PatrickThis study evaluates the tribological properties of DIN 1.2740 hot tool steel against Super Cr13 martensitic stainless steel at 700 °C. The results show that the coefficient of friction (COF) ranged from 0.15 to 0.63, indicating moderate frictional interaction. The wear rate of DIN 1.2740 was observed to be low, suggesting good resistance to wear at high temperatures. The complex surface oxide layer that formed on the pin's top surface, significantly reducing the COF and acting as a solid lubricant at elevated temperatures. The oxide layer was also fragile and unable to withstand the high sliding velocities and high loads. The steel exhibited a high surface roughness when subjected to increasing normal loads and increasing sliding velocities.