• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.4 s.175
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• pp.946-954
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• 2000

The purposes of the paper are to calculate stresses and strains of the disk with overcoating layer rotating quickly under normal loading and shear loading by contacting with head and to present material properties preventing the delamination between the disk and overcoating layer. The hard disk is modeled as two-layered disk composed with overcoating layer and the rest layers and the loading onto the disk is assumed axisymmetric. Solutions to equilibrium equations and compatibility equations are derived with the form of polynimial and Bessel function and coefficients satisfying boundary conditions are obtained differently for the case of body force, normal force and shear force. The risk of delamination are investigated for us to calculate the differences of strains at the interface between the disk and overcoating layer and the material properties preventing delamination are presented by calculating the differences of strains according to Young's modulus and density of disk.

• Journal of Korean Society of Steel Construction
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• v.18 no.6
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• pp.707-716
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• 2006

The optimization of the direct design system of semi-rigid steel frames using advanced analysis and genetic algorithm was presented. Advanced analysis can predict the combined nonlinear effects of connection, geometry, and material on the behavior and strength of semi-rigid frames. Geometric nonlinearity was determined using stability functions. On the other hand, material nonlinearity was determined using the Column Research Council (CRC) tangent modulus and parabolic function. The Kishi-Chen power model was used to describe the nonlinear behavior of semi-rigid connections. The genetic algorithm was used as the optimization technique. The objective function was assumed as the weight of the steel frame, with the constraint functions accounting for load-carrying capacities, deflections, inter-story drifts and ductility requirement. Member sizes determined by the proposed method were compared with those derived using the conventional method.

• Macromolecular Research
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• v.9 no.3
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• pp.129-142
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• 2001

To efficiently demonstrate the molecular motion, physical properties, and mechanical properties of polycarbonates, we studied the differences between bisphenol-A polycarbonate(BPA-PC) and tetramethyl bisphenol-A-polycarbonate(TMBPA-PC) using molecular modeling techniques. To investigate the conformations of BPA-PC and TMBPA-PC and the effect of the conformation on mechanical properties, we performed conformational energy calculation, molecular dynamics calculation, and stress-strain curves based on molecular mechanics method. From the result obtained from conformational energy calculations of each segment, the molecular motions of the carbonate and the phenylene group in BPA-PC were seen to be more vigorous and have lower restriction to mobility than those in TMBPA-PC, respectively. In addition, from the results of radial distribution function, velocity autocorrelation function, and power spectrum, BPA-PC appeared to have higher diffusion constant than TMBPA-PC and is easier to have various conformations because of the less severe restrictions in molecular motion. The result of stress-strain calculation for TMBPA-PC seemed to be in accordance with the experimental value of strain-to-failure ∼4%. From these results of conformational energy calculations of segments, molecular dynamics, and mechanical properties, it can be concluded that TMBPA-PC has higher modulus and brittleness than BPA-PC because the former has no efficient relaxation mode against the external deformations.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.10 s.253
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• pp.1227-1234
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• 2006

Up to now, several mathematical theories based on strain energy functions have been developed for rubber materials. These theories, coupled with the finite element method, can be used very effectively by engineers to analyze and design rubber components. However, due to the complexities of the mathematical formulations and the lack of general guidelines available fur the analysis of rubber components, it is a formidable task for an engineer to analyze rubber components. In this paper a method for predicting strain energy functions - Neo-Hookean model and Mooney-Rivlin model - from the hardness using the empirical equation without any experiment is discussed. First based on the elasticity theories of rubber, the relation between stress and strain is defined. Then for the butyl rubbers, the model constants of Neo-Hookean model and Mooney-Rivlin model are calculated from uniaxial tension tests. From the results, the usefulness of the empirical equation to estimate elastic modulus from hardness is confirmed and, fur Mooney-Rivlin model, the predicted and the experimental model constants are compared and discussed.

• Steel and Composite Structures
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• v.3 no.3
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• pp.185-198
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• 2003

The concept of performance based seismic design has been gradually accepted by the earthquake engineering profession recently, in which the cost-effectiveness criterion is one of the most important principles and more attention is paid to the structural performance at the inelastic stage. Since there are many uncertainties in seismic design, reliability analysis is a major task in performance based seismic design. However, structural reliability analysis may be very costly and time consuming because the limit state function is usually a highly nonlinear implicit function with respect to the basic design variables, especially for the complex large-scale structures for dynamic and nonlinear analysis. Understanding statistical properties of the structural inelastic deformation, which is the aim of the present paper, is helpful to develop an efficient approximate approach of reliability analysis. The present paper studies the statistical properties of the maximum elastoplastic story drift of steel frames subjected to earthquake load. The randomness of earthquake load, dead load, live load, steel elastic modulus, yield strength and structural member dimensions are considered. Possible probability distributions for the maximum story are evaluated using K-S test. The results show that the choice of the probability distribution for the maximum elastoplastic story drift of steel frames is related to the mean value of the maximum elastoplastic story drift. When the mean drift is small (less than 0.3%), an extreme value type I distribution is the best choice. However, for large drifts (more than 0.35%), an extreme value type II distribution is best.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.2
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• pp.155-164
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• 2009

In this paper, a spectral finite element method for a rectangular sandwich plate with viscoelastic core having the Levy-type boundary conditions has been plated. The sandwich plate consists of two isotropic and elastic face plates with a surfaced-bonded viscoelastic core. For the analysis, the in-plane and transverse energy in the face plates and only shear energy in the core are considered, respectively. To account for the frequency dependent complex shear modulus of the viscoelastic core, the Golla-Hughes-McTavish model is adopted. To evaluate the validity and accuracy of the proposed method, the frequency response function and dynamic responses of the sandwich plate with all edges simply supported subject to an impact load are calculated and compared with those calculated by a finite element method. Though these calculations, it is confirmed that the proposed method is very reliable and efficient one for vibration analysis of a rectangular sandwich plate with viscoelastic core having the Levy-type boundary conditions.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.6
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• pp.113-122
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• 2003

Topology optimization is begun with layout optimization that is attributed to Rozvany and Prager of the 1960's. They claimed that structure was transformed into truss connecting all the nodes of finite element and optimized by control of its sectional modulus. But, this method is partial topology optimization. General layout optimal design appliable to continum structure was proposed by Bendsoe and Kikuchi in 1988. Topology optimization expresses material stiffness of structure into function of arbitrary variable. If this variable is 1, material exists but if this variable is 0, material doesn't exist. Therefore, topology optimization searches the distribution function of material stiffness for structure. There are a few researchs for simple engineering problem such as topology optimization of square plane structure or truss structure. So, This study applied to topology optimization of table liner for vertical roller mill that is the largest scale in the world. After table liner decreased by 20% of original weight, the structure analysis for first optimized model was performed.

• The Journal of the Acoustical Society of Korea
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• v.25 no.5
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• pp.222-228
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• 2006

The acoustical property of micro-speaker had been investigated as a function of the diaphragm material in this study. Young's modulus and the density of material is deeply related to the determination of sound velocity and stiffness. As a result, it was appeared that the resonance frequency of micro-speaker was PEI < PPS < PET < PEN. This experimental result was in an excellent agreement with the theoretical one. The increasing ratio of sound pressure level to the frequency between 20Hz and the resonance frequency ($f_s$) and the high resonance frequency ($f_h$) were not affected by the diaphragm material.

• Corrosion Science and Technology
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• v.10 no.3
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• pp.95-100
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• 2011

Protective coatings play an important role in the protection of metallic structures against corrosive environment. The main function of anticorrosive coating is to prevent the materials from corrosive agents, such as water, oxygen and ions. In the study, the corrosion protection properties of urethane and epoxy coating systems were evaluated using EIS methods exposed to the corrosion acceleration test such as Norsok M501, Prohesion and hygrothermal cyclic test. AFM analysis of the coating systems was carried out to monitor the change of roughness of coatings. Urethane coating system was more stable than the epoxy coating under given cyclic conditions. Water uptake into the urethane coatings was less than that into the epoxy coating. The urethane coating system showed better corrosion protection than epoxy coating system based on the changes of the impedance modulus at low frequency region with exposure time. Consequently, the corrosion protection properties of the epoxy and urethane coatings was well correspond with their surface roughness changes and water uptakes.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.30B no.10
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• pp.69-76
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• 1993

In this paper we propose a design of a digital neuron processor using the residue number system for efficient matrix.vector multiplication involved in neural processing. Since the residue number system needs no carry propagation for modulus operations, the neuron processor can perform multiplication considerably fast. We also propose a high speed algorithm for computing the sigmoid function using the specially designed look-up table. Our method can be implemented area-effectively using the current technology of digital VLSI and siumlation results positively demonstrate the feasibility of our method. The proposed method would expected to adopt for application field of digital neural network, because it could be realized to currently developed digital VLSI Technology.