Effects of materials positioning and tool rotational speed on metallurgical and mechanical properties of dissimilar modified friction stir clinching of AA5754-O and AA2024-T3 sheets

YesThe performance of the modified friction stir clinched and friction stir spot welded joints of AA5754-O and AA2024-T3 Al alloy was improved by investigating the impact of material flow influencing parameters such as material positioning and tool rotational speed on the microstructure, mechanical and fracture behaviors of the joints. The results reveal that the positioning of a harder material (AA2024-T3) as the upper plate induces higher peak temperatures in the friction stir clinched (500 °C) and friction stir spot welded (475 °C) joints. This positioning favors inter-material mingling, grain coarsening with inherent higher dislocation density and tangles, and improved tensile failure loads in the AA2024-T3/AA5754-O joint than the AA5754-O/AA2024-T3 joint. The formation of partial weld-center defect declines in the AA2024-T3/AA5754-O at low tool rotational speed due to the better local heat build-up and geometric-differential flow effect in comparison with the AA5754-O/AA2024-T3 counterparts. The positioning of harder Al alloy on the top of a soft Al alloy is thus recommended for the improvement of modified friction stir clinched joints

Modelling of Recrystallization and Grain Boundary Migration by Cellular Automata

Abstract. Within past ten years, the importance of cellular automata (CA) models of both recrystallization and grain boundary migration has been recognized. It can be shown that CA provides a computationally efficient mathematical framework for simulations of physically relevant models of the above processes. Generally, CA works in such models with a vast number of identical copies of several generic processes -as recrystallization, nucleation, grain boundary migration, etc. -which interact locally and results in a complex global response. The attention is focused to some important aspects of recrystallization, grain growth and CA modelling. Finally, possible future development of more physically relevant models are briefly outlined

The Anti-Oriental Narrative of Vambery in Travels in Central Asia

A reader of Travels in Central Asia by Vambery expects a reliable and authentic picture of the history of orient; however, what he/she receives is nothing but a biased and prejudiced narrative mingled with misguided epistemological understanding on the one hand and a high opinion of the West on the other hand. The application of Edward Said’s notions of Orientalism as the theoretical framework in the present study made it possible to identify and highlight such misleading narrations in which the author betrays his reader by imposing anti-orient views in keeping with mere bigotry. Bereft of minimal understanding of the differences between the East and the West, Vambery openly casts doubt concerning the historically established values of the orient against the occident from a variety of vantage points. Vambery recruits a Hungarian anti-orient to prioritize the occident against the orient and employs what Edward Said introduces as distorted knowledge, reductive images and disputatious polemics to accomplish his goal. This study concerns itself with presenting an unbiased reading where both the orient and occident are equally respected rather than prioritized

Generalized Poisson--Nernst--Planck-based physical model of O2_2 I LSM I YSZ electrode

The paper presents a generalized Poisson-Nernst-Planck model of an yttria-stabilized zirconia electrolyte developed from first principles of nonequilibrium thermodynamics which allows for spatial resolution of the space charge layer. It takes into account limitations in oxide ion concentrations due to the limited availability of oxygen vacancies. The electrolyte model is coupled with a reaction kinetic model describing the triple phase boundary with electron conducting lanthanum strontium manganite and gaseous phase oxygen. By comparing the outcome of numerical simulations based on different formulations of the kinetic equations with results of EIS and CV measurements we attempt to discern the existence of separate surface lattice sites for oxygen adatoms and O2- from the assumption of shared ones. Furthermore, we discern mass-action kinetics models from exponential kinetics models

Diffusion brazing of IN738 to SiC ceramic with Ag-Cu-Ti powder: Effect of bonding time on metallurgical and mechanical properties

YesDiffusion brazing of SiC ceramic to IN738 using an Ag-Cu-Ti powder-mixture as an interlayer was carried out for the first time. The impact of the bonding time (30 and 45 min) on metallurgical features and shear strength of the joints was assessed. The results revealed that raising the bonding time resulted in expanding of the brazing layer from 46.98 µm to 55.31 µm. Besides, increasing the bonding time also enhanced the shear strength of the SiC/Ag-Cu-Ti/IN738 joints

Fabrication of AA6061/316 composites via a double pin FSP tool

YesIn this study, a new double pin tool was utilized for the development of AA6061/316 stainless steel reinforced composite by employing the friction stir processing technique for the first time. The microstructure, hardness, tensile, tribological, and corrosion behaviors of the fabricated composites were investigated and comparative assessments were made with the results obtained from the single-pin tool. The results showed that particle-matrix reaction did not occur in the composites irrespective of the nature of the tool profile. The double-pin tool outstandingly boosted the grain refinement (7.01–5.78 μm), particle fragmentation, and distribution within the Al matrix due to the additional pin-assisted plastic deformation, high straining, dynamic recrystallization, and Zener pinning effects. The double-pin tool improved the microhardness (127–141 HV), tensile strength (162–233 MPa), and corrosion resistance of the composite with respect to the single-pin tool counterparts. The replacement of the single pin tool with a double pin tool diminished the specific wear rate (0.38–0.22 mm3/Nm) of the composite. The double-pin tool has a favourable impact on the structure, mechanical, and corrosion behaviours of the AA6061/316 stainless steel reinforced composite. It is thus recommended for composite development

The role of stirring time on the metallurgical and mechanical properties during modified friction stir clinching of AA6061-T6 and AA7075-T6 sheets

YesIn this study, the modified friction stir clinching process was successfully utilized to weld the AA7075-T6 to AA6061-T6 aluminum alloys. The approach of this study was to appraise the influence of the stirring time (6, 12, and 18 s) on the metallurgical and mechanical behavior of the welded samples. The microstructural study demonstrated that stirring time significantly affected joint properties and material flow, which can be ascribed to the discrepancy in the properties of the Al alloys used in this study. Void, local melting and defect-free joints were produced under the stirring times of 6 s, 18 s, and 12 s respectively. It was found that tensile/shear strength increased significantly from 63.5 MPa to 109 MPa as the stirring time increased from 6 s to 12 s, while a further increase in the stirring time to 18 s significantly decreased the joint's strength to 76.1 MPa. The observed failed samples showed that stirring time did not influence fracture mode

Interatomic potentials for atomistic simulations of the Ti-Al system

Semi-empirical interatomic potentials have been developed for Al, alpha-Ti, and gamma-TiAl within the embedded atomic method (EAM) by fitting to a large database of experimental as well as ab-initio data. The ab-initio calculations were performed by the linear augmented plane wave (LAPW) method within the density functional theory to obtain the equations of state for a number of crystal structures of the Ti-Al system. Some of the calculated LAPW energies were used for fitting the potentials while others for examining their quality. The potentials correctly predict the equilibrium crystal structures of the phases and accurately reproduce their basic lattice properties. The potentials are applied to calculate the energies of point defects, surfaces, planar faults in the equilibrium structures. Unlike earlier EAM potentials for the Ti-Al system, the proposed potentials provide reasonable description of the lattice thermal expansion, demonstrating their usefulness in the molecular dynamics or Monte Carlo studies at high temperatures. The energy along the tetragonal deformation path (Bain transformation) in gamma-TiAl calculated with the EAM potential is in a fairly good agreement with LAPW calculations. Equilibrium point defect concentrations in gamma-TiAl are studied using the EAM potential. It is found that antisite defects strongly dominate over vacancies at all compositions around stoichiometry, indicating that gamm-TiAl is an antisite disorder compound in agreement with experimental data.Comment: 46 pages, 6 figures (Physical Review B, in press

Effect of watercress seed mucilage (Lepidium sativum L.) on the wound healing in New Zealand rabbits

Background and aims: Wound healing is one of the most important issues in medical science. Synthetic drugs have long been introduced and used to speed up the healing process of wounds, but most of them have many side effects. The present study was performed to evaluate the healing efficiency of watercress seed mucilage (Lepidium sativum L.) on wounds. Methods: In this study, the animals were randomly divided into five groups. The treatment groups were (1), (2), (3), sham (4), and control (5). The treatment groups were treated with 20%, 10%, and 5% watercress seed mucilage in the Eucerin base, respectively, and the sham was treated with Eucerin, while the control received no treatment. Then, 5 pairs of full-thickness wounds with a diameter of 7 mm were created on both sides of the rabbit’s spine. Macroscopic and wound area studies were performed on days 4, 7, and 14 after surgery. Results: According to the analysis of variance, there was a significant difference between groups 1, 2, 3, sham, and control (P=0.001), but no significant difference was observed between group 3, sham group, and control group (P=0.993). Based on these findings, at the end of the treatment period, group 1 had the highest healing rate and the lowest wound area (1.12±0.77) compared to group 2 (4.42±0.30) and 3 (7.05±0.35), as well as the sham (8.34±1.10) and control (8.50±1.90) groups. Thus, the treatment method of this group has been more effective in wound healing than that of the other treatment groups. Conclusion: It seems that watercress seed mucilage can treat wounds due to its important compounds such as flavonoids, phenols, and vitamins A and C

The Impact of Sanctions and Neo-Liberalism on Women’s Organising in Iran

As in the case of many contemporary movements, Iranian women’s activism is connected into local, international and transnational politics. However, Iranian women’s views of transnational solidarity and perceptions of foreign support for women’s rights in Iran are complicated by the experience of Western foreign policy of the last three decades. This is perceived to have claimed to support women’s rights and liberalism against what is often described as a “conservative theocratic state” but has, in some ways, made it more difficult for women to organise “on the ground” and strengthened the hand of conservative forces both materially and ideologically. Two facets of Western foreign policy towards Iran will be discussed and analysed in relation to their impact on women; firstly, this article will investigate the impact of sanctions and the international isolation of the country since 1979 on women’s organisations. Secondly, it will analyse neo-liberalism and the changing nature of the Iranian state, as well as political elites. Utilising interviews with Iranian women activists conducted in 2009, in addition to April 2015, the article will discuss views of transnational solidarity and the diverse political strategies utilised by women activists and organisations in Iran today