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RISS 인기검색어
- 검색키워드
- 저자 : K. K. Poornesh (검색결과 6 건)
- 무료
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Poornesh, K.K.,Sohn, Y.J.,Park, G.G.,Yang, T.H. Pergamon Press ; Elsevier Science Ltd 2012 International journal of hydrogen energy Vol.37 No.20
The design of robust polymer electrolyte fuel cell requires a thorough understanding of the materials' response of the cell components to the operational conditions such as temperature and hydration. As the electrolyte membrane's mechanical properties are temperature, hydration and rate dependent, its response under cyclic loading is of significant importance to predict the damage onset and thus the membrane lifetime. This article reports on the variation in stress levels in the membrane induced due to the gas-diffusion layer's (GDL) anisotropic mechanical properties while accurately capturing the membrane's mechanical response under time dependent hygrothermomechanical conditions. An observation is made on the evolution of negative strain in the membrane under the bipolar plate channel area, which is an indication of membrane thinning, and the magnitude of this strain found to depend upon the GDL's in-plane mechanical properties. In order to come up with a strategy that reduces the magnitude of tensile stresses evolved in the membrane during the hygrothermal unloading and to increase the membrane's lifetime, we numerically show that by employing a fast hygrothermal loading rate and unloading rate strategy, significant reduction (in this study, nearly 100%) in the magnitude of tensile stresses is achievable. The present study assists in understanding the relation between materials compatibility and durability of fuel cell components.
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Poornesh, K.K.,Lee, Sang-Kyo,Cho, Chong-Du,Choi, Kyu-Won 한국정밀공학회 2010 International Journal of Precision Engineering and Vol.11 No.4
In polymer electrolyte fuel cell (PEFC) system, ideal structural integrity design takes into account the end-to-end load transfer mechanism. Hence, structural durability of cell is dependent of individual layers response to the external clamp loading. Since failure modes of each layer differ from another, multidisciplinary approach is needed to innovative designs. Bipolar plate (BPP) of PEFC is multi-functional layer that has a significant potential for research to avoid its structural failure as well as neighboring layers. To this end, present work investigates the effect of BPP materials on the stress transfer as well as distribution in cell layers based on theoretical investigation for clamping load. Gas-diffusion layer (GDL) / BPP interface has drawn considerable interest among researchers due to its susceptibility for damage failure and other related losses. Hence, investigating the interfacial behavior and relating this to the electrical contact resistance is the key feature in proposed investigation.
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조종두,K. K. Poornesh,김재민 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.3
In this article, a micromechanically motivated constitutive model is presented for nafion membrane to capture the rate, temperature,and hydration dependency under monotonic and cyclic tensile loadings. The basic framework of this model is derived from the Arruda-Boyce viscoplastic model and is modified to include hygrothermal correction factors to show that this model can be manipulated to producereliable results under various virtual testing conditions.
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Xiao, Yang,Poornesh, Kumar K.,Wendling, Loic,Cho, Chongdu Elsevier 2014 Materials letters Vol.124 No.-
Nafion N117 is a kind of polymer electrolyte membrane widely used as the ion exchange material in Ionic Polymer-Metal Composite (IPMC) actuators. The mechanical properties of N117 have a great effect on the performance of IPMC actuators. During the manufacturing of IPMC, the procedure includes heating/annealing, and soaking/drying. The membrane is very sensitive to temperature and humidity conditions, so we believe that returning to the initial conditions, irreversible variation of the mechanical properties has occurred during these treatments. This paper focuses on the effect of thermal and hygroscopic treatments on the mechanical responses of the Nafion N117 membrane. The results obtained from this study showed that no matter the thermal or hygroscopic treatments applied, it would decrease the elastic modulus and yielding stress. Furthermore, this decreasing was mainly showed in the intermolecular response. We also found the treated specimens regardless of thermal and hygroscopic treatments showed a sharp transition from elastic to plastic behavior. (C) 2014 Elsevier B.V. All rights reserved.
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Vaishakh Raju,Poornesh K Koorata,Yogeesh Kamat 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.3
In this study, the effect of graded design in comparison to homogeneous cartilage material is investigated for contact pressure distribution in the human knee joint. Knee implants are assumed a homogeneous material. In reality, cartilages are not homogeneous, and to replicate the heterogeneity of cartilages, a graded design is proposed. Simulation results show improved contact pressure distribution in the knee joint due to the graded composition of cartilages. The results are helpful in designing a new class of implant materials.
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Thermally induced nonlinear optical response and optical power limiting of acid blue 40 dye
S. Pramodini,P. Poornesh,K.K. Nagaraja 한국물리학회 2013 Current Applied Physics Vol.13 No.7
We report the investigations of thermally induced third-order nonlinear optical and optical limiting characterizations for various concentrations of acid blue 40 dye in N,N-Dimethyl Formamide, studied by employing z-scan technique under cw HeeNe laser irradiation at 633 nm wavelength. The samples exhibited nonlinear absorption and nonlinear refraction under the experimental conditions. For lower concentration, the samples display both saturable absorption (SA) and reverse saturable absorption (RSA); whereas with increase in concentration, RSA behaviour prevails. The estimated values of the effective coefficients of nonlinear absorption beff, nonlinear refraction n2 and third-order nonlinear susceptibility c(3) were found to be of the order of 10-2 cm/W, 10-4 esu and 106 esu respectively. Multiple diffraction rings were observed when the samples were exposed to laser beam due to refractive index change and thermal lensing. The effect of concentration and the laser intensity on the selfdiffraction ring patterns was studied experimentally. The acid blue 40 dye also exhibited strong optical limiting properties under cw excitation and reverse saturable absorption is found to be the dominant nonlinear optical process leading to the observed nonlinear behaviour.
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