• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.4
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• pp.353-362
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• 2016

An accurate hysteresis model of an elastomer is important for quantifying viscoelastic energy loss. We suggest a highly nonlinear hyper-viscoelastic constitutive model of elastomers. The model captures a nonlinear viscoelastic characteristic by combining Yeoh's hyperelastic model and Hoofatt's hysteresis model used Neo-Hookean hyperelastic model. Analytical and numerical models were generated from uniaxial cyclic tests of an elastomer under a sinusoidal load with a mean strain of 150%, amplitudes of 20~80%, and frequencies of 0.02~0.2Hz. The viscoelastic model can highly capture the viscoelastic energy loss up to a strain of 230%.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.3
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• pp.361-374
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• 2016

The material property of the rubber has been studied in order to improve the reliability of the finite element model of a lead rubber bearing (LRB) which is a typical base isolator. Rubber exhibits elastic behaviour even within the large strain range, unlike the general structural material, and has a hyper-elastic characteristics that shows non-linear relationship between load and deformation. This study represents the mechanical characteristics of the rubber by strain energy function in order to develop a finite element (FE) model of LRB. For the study, several strain energy functions were selected and mechanical properties of the rubber were estimated with the energy functions. A finite element model of LRB has been developed by using material properties of rubber and lead which were identified by stress tests. This study estimated the horizontal and vertical force-displacement relationship with the FE model. The adequacy of the FE model was validated by comparing the analytical results with the experimental data.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.1
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• pp.9-15
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• 2011

The influence of the strain-rate on the superelastic behaviors of shape memory alloys (SMAs) wires is experimentally and numerically investigated. The one-dimensional SMA constitutive equations considering strain-rate effect is developed. The evolution of stress-strain curves of SMA wires is examined with various strain-rates. Results show that the superelastic behaviors of SMAs may significantly be changed depending on the variation of strain-rate.

• Journal of Korean Society of Steel Construction
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• v.27 no.6
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• pp.493-501
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• 2015

Superelastic shape memory alloys (SMAs) are metallic materials that can automatically recover to their original condition without heat treatment only after the removal of the applied load. These smart materials have been wildly applied instead of steel materials to the place where large deformation is likely to concentrate. In spite of many advantages, superelastic SMA materials have been limited to use in the construction filed because there is lack of effort and research involved with the development of the material model, which is required to reproduce the behavior of superelastic SMA materials. Therefore, constitutive material models as well as algorithm codes are mainly treated in this study for the purpose of simulating their hysteretic behavior through numerical analyses. The simulated curves are compared and calibrated to the experimental test results with an aim to verify the adequacy of material modeling. Furthermore, structural analyses incorporating the material property of the superelastic SMAs are conducted on simple and cantilever beam models. It can be shown that constitutive material models presented herein are adequate to reliably predict the behavior of superelastic SMA materials under cyclic loadings.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.5
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• pp.273-278
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• 2019

In this study, a new simple method for the estimation of hyperelastic material properties by indentation tests is proposed. Among hyperelastic material models, the Yeoh model with three material properties ($C_{10}$, $C_{20}$, $C_{30}$) is adopted to describe the strain energy density in terms of strain invariants. Finite element simulations of the spherical indentation of hyperelastic materials of the Yeoh model with different material properties are performed to establish a database of indentation force-displacement curves. The indentation force-displacement curves are fitted by cubic polynomials, which are approximated as a product of third-order polynomials of ($C_{10}$, $C_{20}$, $C_{30}$). A regression analysis is conducted to determine the coefficients of the equations for the indentation force-displacement curve approximations. A regression equation is used to estimate the hyperelastic material properties. The present method is verified by comparing the estimated material properties with true values.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.875-888
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• 2013

The researches have recently progressed toward the use of the superelastic shape memory alloys (SMAs) to develop new smart control systems that reduce permanent deformation occurring due to severe earthquake events and that automatically recover original configuration. The superelastic SMA materials are unique metallic alloys that can return to undeformed shape without additional heat treatments only after the removal of applied loads. Once the superelastic SMA materials are thus installed at the place where large deformations are likely to intensively occur, the structural system can make the best use of recentering capabilities. Therefore, this study is intended to propose new buckling-restrained braced frames (BRBFs) with superelastic SMA bracing systems. In order to verify the performance of such bracing systems, 6-story braced frame buildings were designed in accordance with the current design specifications and then nonlinear dynamic analyses were performed at 2D frame model by using seismic hazard ground motions. Based on the analysis results, BRBFs with innovative SMA bracing systems are compared to those with conventional steel bracing systems in terms of peak and residual inter-story drifts. Finally, the analysis results show that new SMA bracing systems are very effective to reduce the residual inter-story drifts.

• Journal of Ocean Engineering and Technology
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• v.32 no.4
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• pp.253-260
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• 2018

Recently, the application of non-steel materials in ships and offshore plants is increasing because of the development of various nonlinear materials and the improvement of performance. Especially, hyper-elastic materials, which have a nonlinear stress-strain relationship, are used mainly in marine plant structures or ships where impact relaxation, vibration suppression, and elasticity are required, while elasticity must be maintained, even under high strain conditions. In order to simulate and evaluate the behavior of the hyperelastic material, it is very important to select an appropriate material model according to the strain of the material. This study focused on the selection of material models for hyperelastic materials, such as rubber used in the marine and offshore fields. Tension and compression tests and finite element simulations were conducted to compare the accuracy of the nonlinear material models due to variations in the stretch ratio of hyper-elastic material. Material coefficients of nonlinear material models are determined based on the curve fitting of experimental data. The results of this study can be used to improve the reliability of nonlinear material models according to stretch ratio variation.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.3
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• pp.1-7
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• 2020

Fused filament fabrication (FFF) is a process extruding and stacking materials. PLA materials are one of the most frequently used materials for FFF method of 3D printing. Polylactic acid (PLA)-based materials are among the most widely used materials for FFF-based three-dimensional (3D) printing. PLA is an eco-friendly material made using starch extracted from corn, as opposed to plastic made using conventional petroleum resin; PLA-based materials are used in various fields, such as packaging, aerospace, and medicines. However, it is important to analyze the mechanical properties of theses materials, such as elastic strength, before using them as structural materials. In this study, the reliability of PLA-based materials is assessed through an analysis of the changes in the linear elasticity of these materials under thermal degradation by applying a hyperelastic analytical model.

• Journal of Aerospace System Engineering
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• v.11 no.1
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• pp.28-34
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• 2017

Elastomeric o-ring performance and structure when subjected to a foreign object is studied using finite element analysis (FEA). Elastomeric o-rings have been studied using 2D analysis for a long time. Contact pressure is an important factor in o-ring design. When contact pressure is lower than applied pressure, leaking, vibration, and noise can occur; resulting in decreased output. In this study, we compared 2D and 3D analyses of elastomeric o-rings. Similar results were shown for 2D and 3D contact pressure. However, when an o-ring encounters foreign object matter, 3D analysis is required because contact pressure in every direction needs to be considered. We determined the influence of foreign matter on o-ring performance and structure by analyzing 10 cases with different clearances in a 3D model. Therefore, an o-ring encountering foreign object matter must be analyzed in 3D with the result included in the o-ring design.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.6
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• pp.619-628
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• 2011

Human soft tissues, including muscles, ligaments, skin, and blood vessels, are an interesting subject because damage to them can be observed in everyday life. Besides the lack of available experimental data and the large deformation upon loading, the anisotropic and compressible nature of annulus fibrosus makes it more difficult to find a simple material model. A fiber-reinforced hyperelastic material model is used to determine the stress-strain curves upon uniaxial loading. The energy potential function for annulus fibrosus is composed of three different parts: matrix, fibers, and matrix-fiber interaction, which accounts for the angles between two families of fibers. In this paper, two different types of energy potential function for the matrix are considered, and are inserted into the fiber-reinforced model. The calculated results are compared with the Neo-Hookean model and experimental data, and reasonable agreement is observed overall.