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Rokni M.R.,University of Tehran | Zarei-Hanzaki A.,University of Tehran | Abedi H.R.,Automotive Industries Research and Innovation Center | Haghdadi N.,University of Tehran
Materials and Design | Year: 2012

The present work deals with the microstructure evolution of 7075 aluminum alloy which has been backward thixoextruded in the temperature range of 550-600 °C using different ram diameters and ram displacement velocities. The recrystallization and partial melting (RAP) route has been used to obtain the semi-solid feedstocks for thixoforming. The results indicate that the back extruded microstructures mostly consist of semisolid grains which have been elongated along extrusion direction. The finest semisolid grain size has been obtained at lower deformation temperature and higher equivalent strain. This is attributed to the higher imposed shearing force on the liquid phase which could in turn fragment the grains. The current work also explores the room temperature mechanical properties of thixoformed work-pieces using shear punch testing method. It is found that the room temperature shear strength and ductility values have been substantially influenced by the deformation temperature, ram displacement velocity, and ram diameter. © 2011 Elsevier Ltd. Source


Rokni M.R.,University of Tehran | Zarei-Hanzaki A.,University of Tehran | Abedi H.R.,Automotive Industries Research and Innovation Center
Materials Science and Engineering A | Year: 2012

The present work deals with the microstructural evolution and mechanical properties of 7075 aluminum alloy which has been backward extruded under different deformation conditions. The backward extrusion passes were carried out in the temperature range of 450-520°C using different punch diameters (12 and 15. mm) and punch displacement velocities (5 and 25. mm/min). The results indicate that a combination of different recrystallization mechanisms (i.e., continuous, discontinuous and geometrical ones) may contribute to the formation of new recrystallized grains during applied backward extrusion process. A small specimen testing technique (shear punch testing method) was employed to evaluate the mechanical properties of backward extruded work-pieces at room temperature. The results showed that the corresponding mechanical properties have been improved through applied backward extrusion passes. It is also found that the shear strength and ductility values have been substantially influenced by the deformation temperature and punch velocity and punch diameter. © 2011 Elsevier B.V. Source


Shahri Z.,University of Tehran | Zarei-Hanzaki A.,University of Tehran | Abedi H.R.,Automotive Industries Research and Innovation Center | Fatemi-Varzaneh S.M.,University of Tehran
Materials and Design | Year: 2012

The design and control of thermomechanical processing (TMP) schedule are substantially facilitated by a thorough understanding of the dominant deformation mechanisms and phase transformations which occur in the alloy system under consideration. In this regards due to the effects of deformation history, the results of conventional methods such as dilatometry and thermal analysis are insufficient. In the present work, the hot deformation characteristics of AZ31 magnesium alloy has been studied through applying a series of continuous cooling compression (CCC) tests. The compression tests were conducted as the temperature was continuously reduced from 500 °C to 100 °C. The variations of true stress with true strain (or temperature) were extracted and the critical temperatures were determined. The derived true stress-true strain curves revealed five deviations at 440 ± 5 °C, 350 ± 5 °C, 300 ± 5 °C, 215 ± 5 °C and 150 ± 5 °C, which were properly addressed considering the related microstructural evolutions. © 2011. Source


Ebnali-Heidari M.,Automotive Industries Research and Innovation Center | Chehrezad M.R.,K. N. Toosi University of Technology | Heidari M.E.,Shahrekord University | Shateri A.R.,Shahrekord University
Iran Occupational Health | Year: 2016

Background and aims: Occurrence of crashes and forward collisions as the most frequent types of roads and highways' incidents is mostly resulted by drivers' distraction. Forward collision warning systems (FCWS) are of the technologies which may improve driver's situational awareness, and consequently driving performance. The present study has aimed to design an intelligent forward collision warning system (IFCWS), and evaluate its effect on driving performance. Methods: Driving performance variables including initial reaction time (IRT), movement time (MT), brake reaction time (BRT), frequency if errors (ER) and distance between two vehicles (D), were measured through four various tests (without and with a cognitive secondary in-vehicle task, off/on warning system). Results: The results indicate a significant effect of the secondary task on drivers' reaction time, frequency of errors, and distance between the two vehicles. Moreover, the IFCW system led to a decreased frequency of errors and reaction time. However, the warning system had no significant effect on drivers' movement time. Conclusion: The IFCW system improved driving performance. Further naturalistic studies, with more participants are required to validate the results of the study. © 2016, Tehran University of Medical Sciences and Health Services. All rights reserved. Source

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