Investigation of direct extrusion channel effects on twist extrusion using experimental and finite element analysis

Nouri, Mehran,Mohammadian Semnani, Hamidreza,Emadoddin, Esmaeil,Seop Kim, Hyoung Elsevier 2018 MEASUREMENT -LONDON- Vol.127 No.-

<P><B>Abstract</B></P> <P>Twist extrusion (TE) is a relatively new severe plastic deformation technique in which radial deformation is heterogeneously distributed in the sample. In this research, in order to achieve favorable properties, a direct extrusion (DE) channel was embedded after the twist zone at the bottom of the TE die. The plastic deformation behavior of aluminum alloy 6063 (AA6063) was investigated in the TE process, with and without the DE channel. AA6063 successfully underwent TE under the conditions designed using the finite element analysis. According to the simulation results, a very heterogeneous distribution of the equivalent plastic strain (PEEQ) was observed in TE, while the TE+DE simulation exhibited more homogeneous PEEQ in the central and lateral regions. Microstructural evolution analysis using scanning electron microscope and Vickers microhardness evaluations showed that utilizing the DE channel increased the hardness and provided a more homogenous microstructure. Moreover, tensile testing results indicated an increase in strength and enhanced mechanical properties of the TE+DE processed AA6063.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Innovative twist extrusion was achieved by embedding a direct extrusion channel after the twist zone. </LI> <LI> Finite element analysis showed that the direct extrusion channel decreased sample deformation heterogeneity. </LI> <LI> All data indicated that absence of sufficient back pressure led to distortion and elongation of samples. </LI> <LI> The best microstructure was achieved by combining twist extrusion and direct extrusion channel. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Perfect 2-Colorings of k-Regular Graphs

Piri, Farzaneh,Semnani, Saeed Mohammadian Department of Mathematics 2020 Kyungpook mathematical journal Vol.60 No.2

We study perfect 2-colorings of regular graphs. In particular, we consider the 4-regular case. We obtain a characterization of perfect 2-colorings of toroidal grids.

Recessed Gate Cylindrical Heterostructure TFET, a Device with Extremely Steep Subthreshold Swing

Danial Keighobadi,Saeed Mohammadian Semnani,Mohaddeseh Mohtaram 한국전기전자재료학회 2022 Transactions on Electrical and Electronic Material Vol.23 No.1

In this paper, we present a novel cylindrical gate-all-around heterostructure TFET that benefits from recessed gate architecture to enable line tunneling of charge carriers normal to the gate at InGaAs/InP heterojunction. In the proposed TFET, the channel and drain regions are composed of a wide-bandgap semiconductor which results in a considerable suppression of ambipolar conduction and off-state current. The device characteristics are investigated by numerical simulations and the results indicate impressive switching performance of the proposed transistor. Owing to designed geometry and employed material system, we obtain an extremely steep subthreshold swing, sub 3mv/dec over 6 decades of drain current, sub 60mv/dec over 10 decades of drain current, and average subthreshold swing of 21mv/dec, an on-state to off-state current ratio of about 10 12 , and an on-state current of about 100nA at V GS = 0.3 V. The influence of variations in the device dimensions, doping and bias condition on its electrical characteristics is also studied and discussed physically.

Switching Performance Investigation of a Gate-All-Around Core-Source InGaAs/InP TFET

Danial Keighobadi,Saeed Mohammadian Semnani,Mohaddeseh Mohtaram 한국전기전자재료학회 2021 Transactions on Electrical and Electronic Material Vol.22 No.4

A novel core-source gate-all-around TFET based on InGaAs/InP heterojunction is presented in this paper. In the proposed device, the main current flow mechanism is line tunneling which occurs across a heterojunction composed of a narrowbandgap material of source and a wide-bandgap material of channel. The off-state current and ambipolar conduction are diminished by simultaneously employing two different doping concentrations in the channel region, as well as a wide-bandgap material in drain region. We study the switching performance of the device using a calibrated numerical device simulator. The results indicate impressive performance of the proposed transistor, including an extremely steep subthreshold swing, sub 3mv/dec over 5 decades and sub 60mv/dec over 9 decades of drain current, and average subthreshold swing of about 27mv/dec, and an on-state to off-state current ratio of about 10 11 at V GS = 0.3 V. The impact of variations in the device dimensions, doping and bias condition on its electrical characteristics is also studied and discussed physically.

Computational and Experimental Studies on the Effect Back Pressure on Twist Extrusion Process

Mehran Nouri,Hamidreza Mohammadian Semnani,Esmaeil Emadoddin 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.8

In the current study, aluminium 6063 alloy (AA6063) was successfully gain refined by twist extrusion (TE) technique. TEis a representative severe plastic deformation process to fabricate ultrafine-grained in bulk materials by repetitive passes. In order to investigate the influence of back pressure, a direct extrusion (DE) channel was embedded after the twist zoneand the behavior of AA6063 was investigated and compared with and without this channel. Analyzing microstructuralevolutions by scanning electron microscope and Vickers microhardness evaluations showed that, adding the DE channelincreased the hardness distribution and a more homogenous structure was obtained. Finite element analysis was utilized tostudy the distribution of the equivalent plastic strain (PEEQ) numerically. According to the obtained results, with applyingthe TE process, strain increase was observed all over the sample surface, whereas modeling the DE channel after the twistzone caused a better homogeneity in the PEEQ distribution of the transverse cross-section. The PEEQ distribution duringTE process can be correlated to the extent of grain refinement and the uniformity of ultrafine grains. This method seems tobe very interesting and very promising for the future industrial application.

Effect of Punch Speed on the Formability Behavior of Austenitic Stainless Steel Type 304L

H. Fathi,E. Emadoddin,H. R. Mohammadian Semnani,B. Mohammad Sadeghi 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.3

The aim of the present study is to investigate the effect of punch speed on forming limit diagram (FLD) and the formability of austenitic stainless steel type 304L. Effect of strain rate on the height of dome is studied using the hemispherical punch test. Results of this study show that strain rate has significant effect on FLD in this material and high formability obtains at low strain rate. The safe area of FLD between major and minor strains is extended under low strain rate. It is seen that at low punch speed, failure and fracture occur at the pole region (top of the dome), whereas at higher forming rates, failure occurs close to the flange region. Modeling studies are also carried out using Ls-Dyna to know the region of high stress concentration and to predict the location of fracture. There is good agreement between simulation and experimental results.

Influence of Intermediate Heating in Cross Accumulative Roll-Bonding Process on Planar Isotropy of the Mechanical Properties of Commercial Purity Aluminium Sheet

Mojtaba Dehghan,Fathallah Qods,Mahdi Gerdooei,Hamidreza Mohammadian‑Semnani 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12

In this study, the cross accumulative roll-bonding (CARB) process, as an improved technique of the conventional accumulativeroll-bonding (ARB), was conducted on the AA1050 sheet up to 10 passes in two processing modes. The specimenswere either preheated before the rolling step of CARB passes and promptly roll bonded (warm CARB) or were processedat room temperature (cold CARB). The microstructure of samples was characterized using a scanning electron microscope. The effect of intermediate heat treatment on the planar homogeneity of the mechanical properties in the CARB (and evenARB) deformed sheets has not been examined yet. Hence, the present research focuses on the comparison of the planarisotropy of tensile properties between warm and cold CARB products. Also, the uniformity of microhardness distributionthroughout the thickness of samples was evaluated. The warm CARB presented higher elongation, lower tensile strength andmicrohardness with more uniformity of the microhardness distribution, and also premier planar isotropy of the mechanicalproperties than the cold CARB.