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TRIPLE CENTRALIZERS OF C<sup>*</sup> -ALGEBRAS
Davarpanah, Seyed Mohammad,Omidvar, Mohsen Erfanian,Moradi, Hamid Reza The Kangwon-Kyungki Mathematical Society 2018 한국수학논문집 Vol.26 No.4
In this paper, we extend the concept of double centralizer to triple centralizer and we show that, the triple centralizer is a $C^*$-algebra. Some algebraic properties are investigated.
Advanced Approach to Modify Friction Stir Spot Welding Process
Behrouz Bagheri,Mahmoud Abbasi,Amin Abdollahzadeh,Hamid Omidvar 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.10
Nowadays, friction stir spot welding (FSSW) is used in automotive, rail vehicle construction, the aerospace industry, andelectrical industry. In the current research, a modified version of the FSSW process entitled friction stir spot vibration weldingwas introduced to join Al5083 specimens. The joining specimens were vibrated normal to the tool movement direction,while the joint position cooled by passing coolant through the fixture. Different characteristics of developed joint namelymicrostructure, mechanical properties, corrosion behavior were studied. The results showed that stir zone grain size decreasedsignificantly as the vibration was employed and the joint position was cooled. It was found that vibration enhanced thedynamic recrystallization and coolant decreased the grain growth. Both led to enhanced grain refinement in the stir zone. The results also indicated that shear strength and hardness of the weld region increased as the modified version of FSSWwas applied. Corrosion tests revealed that corrosion resistance increased as the modified method was applied.
Mohammad J. Moradi,Esmaeil Emadoddin,Hamid Omidvar 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12
Conventional and two-step heating transient liquid phase bonding (TLP) experiments of martensitic precipitation hardeningstainless steel 17-4-PH were studied employing AMS 4777 braze filler at temperature of 1050 °C for different times (15 to90 min) to accomplish the ideal brazing condition. The effect of TLP methods and bonding conditions on the microstructureand shear bond strength was investigated. The critical bonding time for isothermal solidification in conventional and two-stepheating TLP was 60 min and 45 min, respectively. The microstructure of isothermal solidification zone consisted of Ni-richsolid solution phase. Eutectic constituents Cr-rich boride and Ni3Siwere formed in the joint centerline in the athermallysolidified zone. In the conventional method planar interface was formed, however in TLP bonding under temperature gradientnon-planar interface was formed, high angel grain boundaries merged at the end of isothermal solidification and homogenousbond was produced. Due to the decrease of athermally solidified zone the shear strength increased by increasing the holdingtime and when using the two-step heating process because of better metal to metal contact, the shear strength was higher. The optimum condition was a temperature gradient TLP in 60 min bonding time, which led to shear strength of 435 MPa.