• Fire Science and Engineering
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• v.30 no.5
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• pp.54-59
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• 2016

Steel is a structural material that is inherently noncombustible. On the other hand, it has high thermal conductivity and the strength and stiffness of the material are reduced significantly when exposed to fire or high temperatures. Because the yield strength and modulus of elasticity of steel are reduced by 70% at $350^{\circ}C$ and less than 50% at $600^{\circ}C$, the load-carrying capacity of steel structure at high temperature rapidly lose. To be accepted as a fire-resisting construction, the fire test should be performed at the certificate authority. On the other hand, the fire test on a full-scale structure is limited by time, space, and high-cost. The analytical method was verified by a comparison with the fire test of H-section columns under compression and thermal analysis based on a finite element method using the ABAQUS program, and the numerical analysis method reported in this study was suggested as a complement of an actual fire test.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.44 no.1
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• pp.23-29
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• 2018

In this study, sequential cross-linked collagen gels were successfully prepared with collagen, which is biomaterial, and acrylamide (AAm), which is a synthetic monomer. The elastic moduli (E) of cross-linked collagen gels were increased from 1.5 to 3.0 kPa by varying of AAm concentrations. In addition, human dermal fibroblasts were encapsulated into the porous pores introduced into the gels, and cell growth and behavior were investigated. Increasing E of the gels led to decreases in cell growth rate, while the cellular glycosaminoglycan (GAG) production level was elevated. Overall, the growth and cellular activity of skin cells were influenced by the extracellular matrix properties of the collagen gels. In conclusion, these results will be highly useful for designing reconstructive skins and various tissue engineering researches.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.917-920
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• 2008

ECC is a special kind of high performance cementititous composite which exhibits typically more than 2% tensile strain capacity by bridging microcracks at a crack section. Therefore, micromechanics should be adopted to obtain multiple cracking and strain hardening behavior. This paper propose a linear elastic analysis method to simulate the multiple cracking and strain hardening behavior of ECC. In an analysis, the stress-crack opening relation modified considering the orientation of fibers and the number of effective fibers is adopted. Furthermore, to account for uncertainty of materials and interface between materials, the randomness is assigned to the tensile strength(${\sigma}_{fci}$), elastic modulus($E_{ci}$), peak bridging stress(${\sigma}_{Bi}$) and crack opening at peak bridging stress(${\delta}_{Bi}$), initial stress at a crack section due to chemical bonding, (${\sigma}_{0i}$), and crack spacing(${\alpha}_cX_d$). Test results shows the number of cracking and stiffness of cracked section are important parameters and strain hardening behavior and maximum strain capacity can be simulated using the proposed method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.4
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• pp.383-389
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• 2011

In this paper, a statistical calibration method is proposed in order to identify the variability of complex modulus for a rubber material due to operational temperature and experimental/model errors. To describe temperature- and frequency-dependent material properties, a fractional derivative model and a shift factor relationship are used. A likelihood function is defined as a product of the probability density functions where experimental values lie on the model. The variation of the fractional derivative model parameters is obtained by maximizing the likelihood function. Using the proposed method, the variability of a synthetic rubber material is estimated and applied to a rubber mount problem. The dynamic characteristics of the rubber mount are calculated using a finite element model of which material properties are sampled from Monte Carlo simulation. The calculated dynamic stiffnesses show very large variation.

• Geomechanics and Engineering
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• v.21 no.6
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• pp.571-582
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• 2020

Aiming at the mechanical and structural characteristics of the contact zone composite rock, the uniaxial compression tests and numerical studies were carried out. The interaction forms and formation mechanisms at the contact interfaces of different materials were analyzed to reveal the effect of interaction on the mechanical behavior of composite samples. The research demonstrated that there are three types of interactions between the two materials at the contact interface: constraint parallel to the interface, squeezing perpendicular to the interface, and shear stress on the interface. The interaction is mainly affected by the differences in Poisson's ratio and elastic modulus of the two materials, stronger interface adhesion, and larger interface inclination. The interaction weakens the strength and stiffness of the composite sample, and the magnitude of weakening is positively correlated with the degree of difference in the mechanical properties of the materials. The tensile-shear stress derived from the interaction results in the axial tensile fracture perpendicular to the interface and the interfacial shear facture. Tensile cracks in stronger material will propagation into the weaker material through the bonded interface. The larger inclination angle of the interface enhances the effect of composite tensile/shear failure on the overall sample.

• International Journal of Fluid Machinery and Systems
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• v.3 no.4
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• pp.342-351
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• 2010

During the operation of a hydro turbine the fluid mechanical pressure loading on the turbine blades provides the driving torque on the turbine shaft. This fluid loading results in a structural load on the component which in turn causes the turbine blade to deflect. Classically, these mechanical stresses and deflections are calculated by means of finite element analysis (FEA) which applies the pressure distribution on the blade surface calculated by computational fluid dynamics (CFD) as a major boundary condition. Such an approach can be seen as a one-way coupled simulation of the fluid structure interaction (FSI) problem. In this analysis the reverse influence of the deformation on the fluid is generally neglected. Especially in axial machines the blade deformation can result in a significant impact on the turbine performance. The present paper analyzes this influence by means of fully two-way coupled FSI simulations of a propeller turbine utilizing two different approaches. The configuration has been simulated by coupling the two commercial solvers ANSYS CFX for the fluid mechanical simulation with ANSYS Classic for the structure mechanical simulation. A detailed comparison of the results for various blade stiffness by means of changing Young's Modulus are presented. The influence of the blade deformation on the runner discharge and performance will be discussed and shows for the configuration investigated no significant influence under normal structural conditions. This study also highlights that a two-way coupled fluid structure interaction simulation of a real engineering configuration is still a challenging task for today's commercially available simulation tools.

• Journal of the Korean GEO-environmental Society
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• v.13 no.8
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• pp.35-43
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• 2012

Construction of sheet pile retaining walls in urban and coastal regions has resulted in sheet pile walls in close proximity to laterally loaded pile foundations. However, there is currently little information available in the literature to assist engineers for quantifying the response of sheet pile walls. This study provides a quantitative method for estimating sheet pile wall response due to loads imposed from a nearby laterally loaded pile. Three dimensional finite element analyses using commercial software, ABAQUS, were performed to assess the response of a sheet pile wall and nearby laterally loaded pile. The soils were modeled using Drucker-Prager constitutive model with associated flow rule, and the sheet pile wall and pile foundation were assumed to behave linear elastic. Four parameters were investigated: sheet pile wall bending stiffness, distance from the pile face to the wall, excavation depth in front of the sheet pile wall, and elastic modulus of the soil. Results from the analyses have been used to develop preliminary design charts and simple equations for estimating the maximum horizontal displacement and maximum bending moment in the sheet pile wall.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.2
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• pp.921-926
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• 2015

Embossed aluminum sheets were been used in heat insulation purpose for automative exhaust parts because of increasing their surface areas and stiffness reinforcement. However, there are many restrictions because of high rate of wrinkle occurrence on press working. We have performed the tensile and bending tests for embossed sheets to clarity its mechanical properties and springback characteristics. Embossed aluminum sheets showed a different flow stress after plastic yielding due to flattening the embossed cone shape. Above all, yield stress of parallel embossed specimen decreases while its diagonal one increases and the decrease of young's modulus in the embossed sheets contributes to the increase of springback amount.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.4
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• pp.1999-2004
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• 2011

This research aims to develop polymer composites which can be used for PEMFC bipolar plate by injection molding process. Considering the moldability and stiffness, we used LCP(Liquid crystal polymer) as base resin. In order to improve electrical conductivity and mechanical properties, we chose carbon black, and both synthetic graphite and expanded graphite. The composites with different recipe are prepared for injection molding of PEMFC bipolar plate and CAE(Computer Aided Engineering) analysis was performed to predict melt flow and fiber orientation We did successfully fabricate the ASTM specimens by injection molding, and measure the electrical conductivity of the samples by using four point probe device. We measured mechanical properties such as flexural strength, flexural modulus and Izod impact strength. Conclusively, the electrical conductivity increased with increasing additive concentration, but both flexural strength and Izod impact strength decreased due to the brittle nature of carbon-based additives.

• Journal of Korean Society of Steel Construction
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• v.18 no.2
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• pp.225-237
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• 2006

Based on the study conducted by Kim et al. (205a, b), an improved stability design method for evaluating the effective buckling lengths of beam-column members is proposed herein, using system elastic/inelastic buckling analysis and second-order elastic analysis. For this purpose, the stress-strain relationship of a column is inversely formulated from the reference load-carrying capacity proposed in design codes, so as to derive the tangent modulus of a column as a function of the slenderness ratio. The tangent stiffness matrix of a beam-column element is formulated using the so-called "stability functions," and elastic/inelastic buckling analysis Effective buckling lengths are then evaluated by extending the basic concept of a single simply-supported column to the individual members as one component of a whole frame structure. Through numerical examples of several structural systems and loading conditions, the possibilities of enhancement in stability design for frame structures are addressed by comparing their numerical results obtained when the present design method is used with those obtained when conventional stability design methods are used.