• Advanced Composite Materials
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• v.16 no.4
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• pp.315-334
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• 2007

In the present study, chopped henequen natural fibers without and with surface modification by electron beam (E-beam) treatment were incorporated into a polypropylene matrix. Prior to composite fabrication, a bundle of raw henequen fibers were treated at various E-beam intensities from 10 kGy to 500 kGy. The effect of E-beam intensity on the interfacial, mechanical and thermal properties of randomly oriented henequen/polypropylene composites with the fiber contents of 40 vol% was investigated focusing on the interfacial shear strength, flexural and tensile properties, dynamic mechanical properties, thermal stability, and fracture behavior. Each characteristic of the material strongly depended on the E-beam intensity irradiated, showing an increasing or decreasing effect. The present study demonstrates that henequen fiber surfaces can be modified successfully with an appropriate dosage of electron beam and use of a low E-beam intensity of 10 kGy results in the improvement of the interfacial properties, flexural properties, tensile properties, dynamic mechanical properties and thermal stability of henequen/polypropylene composites.

• Structural Engineering and Mechanics
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• v.59 no.2
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• pp.343-371
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• 2016

In this paper thermo-mechanical vibration analysis of a porous functionally graded (FG) Timoshenko beam in thermal environment with various boundary conditions are performed by employing a semi analytical differential transform method (DTM) and presenting a Navier type solution method for the first time. The temperature-dependent material properties of FG beam are supposed to vary through thickness direction of the constituents according to the power-law distribution which is modified to approximate the material properties with the porosity phases. Also the porous material properties vary through the thickness of the beam with even and uneven distribution. Two types of thermal loadings, namely, uniform and linear temperature rises through thickness direction are considered. Derivation of equations is based on the Timoshenko beam theory in order to consider the effect of both shear deformation and rotary inertia. Hamilton's principle is applied to obtain the governing differential equation of motion and boundary conditions. The detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of several parameters such as porosity distributions, porosity volume fraction, thermal effect, boundary conditions and power-low exponent on the natural frequencies of the FG beams in detail. It is explicitly shown that the vibration behavior of porous FG beams is significantly influenced by these effects. Numerical results are presented to serve benchmarks for future analyses of FG beams with porosity phases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.9
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• pp.1201-1212
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• 1999

A numerical analysis is performed to predict the thermal response and ablation rate for charring or non-charring material which is designed to be used as thermal protection system (TPS). The numerical program composed of in-depth energy balance equation and the aerotherm chemical equilibrium (ACE) program. The ACE program calculates various thermochemical state from ablation products. The developed numerical program is verified by comparing the reported results from literature. The sensitivity tests for input parameters are performed. The thermal behavior of ablating material is mainly affected by density of ablating material, convective heat transfer coefficient and recovery enthalpy of flow field.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.4
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• pp.330-335
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• 2012

A characteristic behavior of the thermal storage tank for varying thermal load in heat pump water heater was studied. The control method was suggested and applied. By measuring the temperature within the storage tank, the heat pump was ON/OFF controlled. The appropriate measuring position and the size of heat exchanger gives the minimized power consumption of heat pump. As the length of heat exchanger increases, the temperature measuring position goes down of the storage tank and the power consumption increases.

• Advances in nano research
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• v.4 no.3
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• pp.197-228
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• 2016

In the present study, thermo-electro-mechanical vibration characteristics of functionally graded piezoelectric (FGP) Timoshenko nanobeams subjected to in-plane thermal loads and applied electric voltage are carried out by presenting a Navier type solution for the first time. Three kinds of thermal loading, namely, uniform, linear and non-linear temperature rises through the thickness direction are considered. Thermo-electro-mechanical properties of FGP nanobeam are supposed to vary smoothly and continuously throughout the thickness based on power-law model. Eringen's nonlocal elasticity theory is exploited to describe the size dependency of nanobeam. Using Hamilton's principle, the nonlocal equations of motion together with corresponding boundary conditions based on Timoshenko beam theory are obtained for the free vibration analysis of graded piezoelectric nanobeams including size effect and they are solved applying analytical solution. According to the numerical results, it is revealed that the proposed modeling can provide accurate frequency results of the FGP nanobeams as compared to some cases in the literature. In following a parametric study is accompanied to examine the effects of several parameters such as various temperature distributions, external electric voltage, power-law index, nonlocal parameter and mode number on the natural frequencies of the size-dependent FGP nanobeams in detail. It is found that the small scale effect and thermo-electrical loading have a significant effect on natural frequencies of FGP nanobeams.

• Korean Journal of Materials Research
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• v.33 no.10
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• pp.422-429
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• 2023

High-strength low-alloy steel is one of the widely used materials in onshore and offshore plant engineering. We investigated the alloying effect of solute atoms in α-Fe based alloy using ab initio calculations. Empirical equations were used to establish the effect of alloying on the Vicker's hardness, screw energy coefficient, and edge dislocation energy coefficient of the steel. Screw and edge energy coefficients were improved by the addition of V and Cr solute atoms. In addition, the addition of trace quantities of V, Cr, and Mn enhanced abrasion resistance. Solute atoms and contents with excellent mechanical properties were selected and their thermal conductivity and thermal expansion behavior were investigated. The addition of Cr atom is expected to form alloys with low thermal conductivity and thermal expansion coefficient. This study provides a better understanding of the state-of-the-art research in low-alloy steel and can be used to guide researchers to explore and develop α-Fe based alloys with improved properties, that can be fabricated in smart and cost-effective manners.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.12 no.1
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• pp.41-48
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• 2016

To investigate the effect of long-term thermal aging on the microstructural and mechanical characteristics of weldment made of nickel base alloy and its weld metal, an accelerated heat treatment was applied to simulate the process of long-term thermal aging in the operating condition of nuclear power plant. A representative nickel-based weldment with Alloy 600 and Alloy 182 was fabricated and heat-treated at $400^{\circ}C$ for 1,713 h and 3,427 h to simulate the thermal aging for the period equivalent to 15 and 30 years in operating pressurized water reactors, respectively. The microstructural and mechanical characteristics were analyzed by using optical microscopy, scanning electron microscopy and Vickers microhardness measurement. Changes were observed in precipitation behavior and microhardness of each specimen, and these changes were mainly attributed to the change in precipitated morphology and residual stress across the weld during the thermal aging process.

• Journal of ILASS-Korea
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• v.4 no.3
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• pp.42-52
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• 1999

An effectiveness of thermal utilization of a dousing system in the 600 MW PHWR Nuclear Power Plant has been evaluated. The behavior and conditions of water droplet sprayed in a postulated accident conditions in containment configuration has been calculated. In this calculation, two pressure conditions with the consideration of obstruction area and containment wall effect has been established : one being the minimum containment pressure of 7 kPa(g) encountered for dousing shut off and the other being the containment design pressure 124 kPa(g). The results revealed that the effectiveness of the thermal utilization ranges from 93% to 97%. In the analysis on two cases without/with side wall effect in the containment building, the thermal utilization decreases with obstruction area from 89% to 85%, which satisfies the design criteria set for the containment pressure against the accident condition.

• Journal of Mechanical Science and Technology
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• v.17 no.3
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• pp.400-408
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• 2003

A study on the progressive inelastic deformation behavior of the 316 L stainless steel cylindrical structure with plate-to-shell junction under moving temperature front was carried out by structural test and analysis. The structural test intends to simulate the thermal ratcheting behavior occurring at the reactor baffle of the liquid metal reactor as free surface of hot sodium pool moves up and down under plant transients. The thermal ratchet load that heats the specimen up to 550$^{\circ}C$ was applied repeatedly and residual deformation was measured. The thermal ratcheting test was carried out with two types of cylindrical structures, one with plate to-shell junction and the other without the junction to investigate the effects of the geometric discontinuities on the global ratcheting deformation. The temperature distributions of the test specimens were measured and were used for the ratcheting analysis. The ratchet deformations were analyzed with the constitutive equation of the non-linear combined hardening model. The analysis results were in good agreement with those of the structural tests.

• YAKHAK HOEJI
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• v.43 no.2
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• pp.263-273
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• 1999

When glutamate was infected intrathecally, the result is similar to those produced by TPA injected. The involvement of protein kinase C (PKC) in the nociceptive responses in rat dorsal horn neurons of lumbar spinal cord was studied. In test with formalin, a PKC inhibitor (chelerythrine) inhibited dose-dependently the formalin-induced behavior response. Neomycin also inhibited it significantly. But, a PKC activator (12-O-tetradecanoylphorbol-13-ester, TPA) showed reverse effect. When gluatamate was injected intrathecally, we observed the result is smilar to those produced by TPA injection. On the other hand, intrathecal injection of glutamate induced thermal and mechanical hyperalgesia. In Tail-flick test, we examined the involvement of PKC on the glutamate-indeced thermal hyperalgesia. Chelerythrine showed an inhibitory effect and TPA enhanced thermal response. Glutamate decreased the mechanical threshold significantly. A pretreatment of chelerythrine and neomycin inhibited glutamate-induced mechanical hyperalgesia, but the effect of neomycin was not significant. TPA had little effect on the mechanical nociceptive response. These results suggest that the PKC activation through metabotropic receptor at postsynaptic region of spinal cord dorsal horn neurons may influence on the persistent nociception produced by chemical stimulation with formalin, thermal and mechanical hyperalgesia induced by glutamate.