• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.247-250
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• 2009

본 연구에서는 반복하중을 받는 구리 나노와이어에서 나타나는 초탄성 거동을 분자동역학 전산모사를 통해 해석하였다. 나노스케일에서는 표면적 대 부피비가 매우 크기 때문에 표면효과가 지배적으로 나타난다. 이로 인해 벌크상태에서는 보이지 않던 새로운 성질들이 나노크기에서 나타나는데, 이러한 효과로 인해 나노와이어의 경우에는 초탄성 거동을 보인다. 초탄성 거동은 나노와이어의 결정학적 방향의 재배열에 의한 것으로써, 하중을 받는 동안 나노와이어의 결정 구조는 변하지 않으며, 쌍정의 발생 및 쌍정계면의 전파에 의해 결정학적 방향이 재배열된다. 재배열에 의해 부분적으로 변형되었던 나노와이어는 하중을 제거하거나 하중의 방향이 바뀜에 따라 원래의 상태를 회복하는 거동을 보이게 된다. 본 연구에서는 분자 동역학 전산 모사를 통해 <100>/{100} 구리 나노와이어가 반복적인 압축-인장 거동 하에서 초탄성을 보이게 됨을 확인하였으며, 반복 하중 싸이클을 증가시키는 전산모사를 통해 나노와이어의 초탄성이 영구적으로 유지됨을 확인하였다.

• 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 the Korean Society for Aeronautical & Space Sciences
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• v.36 no.8
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• pp.740-746
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• 2008

In this paper, robust structural design of the PEMFC stack gasket is pursued with Taguchi method by considering the noise factor in stack assembly. The study of noise problem in stacking is required to secure the safety and performance improvement of PEMFC stack. The design parameters in the Taguchi method are selected so that the structural responses are insensitive to the noise factors. In the gasket analysis, a Mooney-Rivlin strain energy function is used to consider hyperelasticity between load and displacement. By uni-axial and equi-biaxial tension tests of the gasket, the material properties are determined for the use in robust design of PEMFC gasket. The robust design of the PEMFC stack may provide structural reliability.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.4
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• pp.413-420
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• 2023

Among the seismic structures for reducing earthquake damage, the seismic control structure is a technology that can efficiently improve seismic performance and secure economic feasibility by simply applying a damper. However, existing dampers have limitations in terms of durability due to required seismic performance and material plasticity. In this study, we proposed a polyurethane damper with enhanced recovery characteristics by applying precompression to polyurethane, which basically shows elastic characteristics, and applying superelastic shape memory alloy (SSMA). To verify the characteristics of the polyurethane damper, the concept was first established, and the design details were completed by selecting SSMA and steel, and selecting the precompression size as design variables. In addition, structural tests were conducted to derive response behavior and analyze force resistance performance, residual displacement, recovery rate, and energy dissipation capacity. As a result of the analysis, the polyurethane damper showed that various performances improved when the SSMA wire was applied and the precompression increased.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.102.1-102.1
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• 2012

Ti 및 Ti 합금은 치과 및 정형외과 등의 분야에서 생체재료로써 다양한 용도로 적용되고 있으며, 보다 안전하고 우수한 특성의 Ti 합금 개발에 대한 관심이 높아지고 있다. 본 연구에서는 Ti-Nb-Ge 합금의 초탄성 특성에 미치는 집합조직의 영향에 대해 조사하였다. 집합조직 제어를 위해 등속 및 이주속 압연을 적용한 후 $850^{\circ}C$에서 30분~2시간까지 어닐링하였다. 광학현미경과 SEM-EBSD를 이용하여 미세조직 및 집합조직을 분석하고, 순환식 인장시험을 통해 시편의 초탄성 특성을 평가하였다. 등속압연 후 어닐링한 시료의 경우 alpha-fiber 집합조직이 발달하는 한편, 이속압연 후 어닐링한 시료는 {113}// 및 {331}의 집합조직이 발달하는 것으로 나타났다. 마르텐사이트 변태에 의한 변형회복능과 집합조직 성분별 강도의 관계를 비교한 결과, alpha-fiber 집합조직이 발달할수록 변형회복능이 증가하는 것으로 나타났다.

• 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.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 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.1
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• pp.11-17
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• 2024

A seismic structure is an earthquake-resistant design that dissipates seismic energy by equipping the structure with a device called a damper. As research efforts to reduce earthquake damage continue to rise, technology for isolating vibrations in structures has evolved by altering the materials and shapes of dampers. However, due to the inherent nature of the damper, there are an unescapable restrictions on the extent of plastic deformation that occurs in the material to effectively dissipate energy. Therefore, in this study, we proposed a long-life damper that offers semi-permanently usage and enhances structural performance by applying additional tension which is achieved by utilizing super elastic shape memory alloy (SSMA), a material that self-recovers after deformation. To comprehensively understand the behavior of long-life dampers, finite element analysis was performed considering the design variables such as material, wire diameter, and presence of tension, and response behavior was derived to analyze characteristics such as load resistance, energy dissipation, and residual displacement to determine the performance of long-life dampers in seismic structure. Excellence has been proven from finite element analysis results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.7
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• pp.642-650
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• 2008

In this paper, structural behavior of Gasket and GDL of a PEMFC stack is studied to improve the performance and to secure the safety. In the Gasket analysis Mooney-Rivlin strain energy function is used to consider hyperelasticity of load and displacement. The material properties is determined by testing specimens of the gasket at uni-axial and equi-biaxial mode and compared with finite element analysis results. By measuring a thickness change, the material property of GDL is determined. The pressure drop of a unit cell is measured along the channel for the clamping force. A cross sectional change of channel base on the experimental data is obtained experimentally and compare with FEM analysis results.