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RISS 인기검색어
- 검색키워드
- 저자 : Amir Momeni (검색결과 4 건)
- 무료
- 기관 내 무료
- 유료
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Robust Observer-based H_∞ Control of a Markovian Jump System with Different Delay and System Modes
Amir Hossein Abolmasoumi,Hamid Reza Momeni 제어·로봇·시스템학회 2011 International Journal of Control, Automation, and Vol.9 No.4
This paper investigates the problem of robust observer-based stabilization for a delayed Markovian jump system. The sources of randomness in the system mode and the delay mode are assumed to be different. To this end, two different Markov processes are considered for modeling the randomness of the system matrices and the state delay. A two mode-dependent Lyapunov-Krasovskii functional is used to design a robust observer based feedback control rule for the stochastic stability of the closed-loop system. The rule4 should also satisfy the condition of disturbance reduction at a prescribed level in the presence of parametric uncertainties. The procedure is implemented by solving linear matrix inequalities (LMIs). The results are tested within a simulation example and the effectiveness of the proposed design method is verified.
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Influence of Graphene Oxide Nanoplates on Strengthening Mechanism of Al6061-GO Nanocomposites
Mahdi Hedayatian,Amir Momeni 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.1
In this paper, the effect of graphene oxide (GO) nanoplates on the strengthening mechanism of Al6061-GO nanocompositeshave been investigated. To make composite samples, GO nanosheets with various weight percents of 0.0, 0.2, 0.5, and 0.8%were added to the molten Al6061 through the stir casting method. Then the cast composite slabs were hot rolled. Tensiletest was used to study the mechanical properties of composite specimens. The experimental results showed that the nanoplatesof GO have strong strengthening effects along with increase in ductility in the fabricated composites. To model thestrengthening effect of GO in Al6061 matrix, the modified shear-lag and the modified Zhang-Chen strengthening mechanismshave been utilized. Comparisons between the model predictions and the experimental results revealed that both models cansatisfactorily predict the yield strength of fabricated nanocomposites.
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Constitutive Analysis and Processing Map for Hot Working of a Ni-Cu Alloy
Gholam Reza Ebrahimi,Amir Momeni,Seyed Mehdi Abbasi,Hossein Monajatizadeh 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.1
The hot deformation behavior of a Ni-Cu alloy was studied using hot compression testing in the temperature range of 950 °C-1150 °C and at strain rates of 0.001 s.1-1 s.1. Flow curves at low strain rates, up to 0.01 s.1, were typical of DRX characterized by a single peak, while at higher strain rates, the typical form of a DRX flow curve was not observed. The power-law constitutive equation was used to correlate flow stress to strain rate and temperature, and the apparent activation energy of hot deformation was determined to be about 462.4 kJ/mol. The peak strain and stress were related to the Zener-Hollomon parameter and the modeling formula was proposed. The dependence of flow stress to the Z changed at ln Z=38.5,which was considered to be a critical condition for the change in the mechanism of dynamic recrystallization. The efficiency of power dissipation was determined to be between 10-35 percent at different deformation conditions. According to the dynamic material model, stable flow was predicted for the studied temperature and strain rate ranges. Highly serrated grain boundaries at low strain rates were considered to be a reason for the occurrence of continuous dynamic recrystallization. On the contrary, at high strain rates, equiaxed grain structure was attributed to the typical discontinuous dynamic recrystallization.
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Microstructural and Mechanical Behavior of Al6061-Graphene Oxide Nanocomposites
Mahdi Hedayatian,Khodadad Vahedi,Alireza Nezamabadi,Amir Momeni 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.6
In this paper, the mechanical properties and microstructure of Al6061-graphene oxide (GO) nanocomposites material, producedby stir casting and hot rolling process have been investigated. In order to make composite samples, GO nanoplateswith various weight percents of 0.2, 0.5 and 0.8% were added to the molten Al6061 through the stir casting process. Thenthe cast composite slabs were hot rolled at 530 °C. Tensile and hardness tests were used to study the mechanical propertiesof nanocomposite specimens. The microstructures of samples were examined by optical and scanning electron microscopes. The scanning electron microscope images and energy dispersive spectroscopy map analyses showed that the GO nanoplateshave been uniformly distributed within the Al matrix. The mechanical test results showed considerable improvements inthe hardness (by 41%), yield strength (by 43%), tensile strength (by 38%), ductility (by 58%) and toughness (by 116%) ofthe composite samples with respect to the base alloy. Studying the fracture surface also showed that ductile fracture is thedominant mechanism of fracture in all the specimens.
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