• Smart Structures and Systems
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• v.16 no.1
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• pp.183-194
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• 2015

Shape memory alloy (SMA) helical springs have found a large number of different applications in industries including biomedical devices and actuators. According to the application of SMA springs in different actuators, they are usually under tension and torsion loadings. The ability of SMAs in recovering inelastic strains is due to martensitic phase transformation between austenite and martensite phases. Stress or temperature induced martensite transformation induced of SMAs is a remarkable property which makes SMA springs more superior in comparison with traditional springs. The present paper deals with the simulation of SMA helical spring at room temperature. Three-dimensional phenomenological constitutive model is used to describe superelastic behavior of helical spring. This constitutive model is implemented as a user subroutine through ABAQUS STANDARD (UMAT), and the process of the implementation is presented. Numerical results show that the developed constitutive model provides an appropriate approach to captures the general behavior of SMA helical springs.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.2
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• pp.275-282
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• 2002

Tensile residual stress happen by difference of coefficients of thermal expansion between fiber and matrix is one of the serious problems in metal matrix composite(MMC). In this study, TiNi fiber was used to solve the tensile residual stress as the reinforced material. TiNi fiber improves the tensile strength of composite by occurring compressive residual stress in matrix using shape memory effect of it. Pre-strain was added to generate compressive residual stress inside TiNi/A16061 composite. It was also evaluated the effect of compressive residual stress corresponding to pre-strains variation. AE technique was used to clarify the microscopic damage behavior at high temperature and the effect of pre-strain difference of TiNi/A16061 shape memory alloy composite.

• Proceedings of the Korean Society of Rheology Conference
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• 2000.11a
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• pp.7-10
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• 2000

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2000.11a
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• pp.46-46
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• 2000

• Smart Structures and Systems
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• v.24 no.1
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• pp.111-125
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• 2019

Metallic shape memory alloys present fascinating physical properties such as their super-elastic behavior in austenite phase, which can be exploited for providing a structure with both a self-centering capability and an increased ductility. More or less accurate numerical models have been introduced to model their behavior along the last 25 years. This is the reason for which the literature is rich of suggestions/proposals on how to implement this material in devices for passive and semi-active control. Nevertheless, the thermo-mechanical coupling characterizing the first-order martensite phase transformation process results in several macroscopic features affecting the alloy performance. In particular, the effects of day-night and winter-summer temperature excursions require special attention. This aspect might imply that the deployment of some devices should be restricted to indoor solutions. A further aspect is the dependence of the behavior from the geometry one adopts. Two fundamental lacks of symmetry should also be carefully considered when implementing a SMA-based application: the behavior in tension is different from that in compression, and the heating is easy and fast whereas the cooling is not. This manuscript focuses on the passive devices recently proposed in the literature for civil engineering applications. Based on the challenges above identified, their actual feasibility is investigated in detail and their long term performance is discussed with reference to their fatigue life. A few available semi-active solutions are also considered.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.5
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• pp.287-297
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• 2022

This paper presents experimental and analytical studies on the lateral cyclic behavior of RC columns actively confined with iron-based shape memory alloy (Fe-SMA) strips. Based on the Anexperimental study, we investigated the effectiveness of active confinement through compression testings of concrete cylinders confined by Fe SMA strips and carbon fiber-reinforced polymer (CFRP) sheets. The test results showed that the specimens confined with Fe SMA strips significantly increased the deformation capacity of the concrete, even under lower confining pressures, compared to those specimensconfined with CFRP sheets. The experimental results were used to develop finite-element models of RC columns confined with Fe SMA or CFRP in their plastic-hinge region. After validating the proposed analytical model through comparison with the results from a previous RC column test, a series of lateral cyclic load analyses were carried out for the RC columns confined with Fe SMA and CFRP. The analytical results revealed that the lateral cyclic behavior of the Fe SMA-confined column was greatly enhanced in terms of deformation and energy dissipation capacities compared with tothat of the as-built and CFRP-confined columns.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.9
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• pp.1787-1794
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• 2002

TiNi alloy fiber was used to solve the problem of the tensile residual stress as the reinforced material. TiNi alloy fiber improves the tensile strength of composite by occurring compressive residual stress in the matrix using shape memory effect. In order to generate compressive residual stress in TiNi/Al6061 shape memory alloy(SMA) composite, 1, 3 and 5% pre-strains were applied to the composite in advance. It was also evaluated the effect of compressive residual stress corresponding to the pre-strain variation and the volume fraction of TiNi alloy. AE technique was used to clarify the microscopic damage behavior at high temperature and the effect of pre-strain in TiNi/Al6061 SMA composite. The results of the microscopic damage evaluation of TiNi/Al6061 SMA composite under various pre-strain using AE technique can be divided into three stage corresponding to the AE signals. AE counts and events were useful parameters to evaluate the fracture mechanism according to the variation of pre-strain. In addition, two dimensional AE source location technique was applied for monitoring the crack initiation and propagation in composite.

• The Korean Journal of Rheology
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• v.9 no.1
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• pp.33-39
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• 1997

PCL, MDI, BD 및 DMPA를 이용, 폴리우레탄(PU)을 ionomer 및 nonionomergudxo 로 제조하였으며 이때 연질성분의 함량(SSC) 및 길이가 PU의 기계적, 동적기계적 특성은 물론 형상기억특성에 미치는 영향을 연구하였다. Ionomer는 nonionomer에 비하여 경도, 탄 성율 및 강도가 모두 우수하였으며 그 효과는 실온에서 경질성분의 함량(HSC)이 높은 PU 일수록 보다 뚜렷하였는데 이는 HSC가 증가할수록 ion 중심의 농도가 증가하며 ion 중심간 의 Coulob 력이 고온보다 실온에서 보다 큰데 기인하는 것으로 해석하였다. 반복인장하중실 험에서 ionomer는 nonionomer에 비해 회복변형이 크고 잔류변형이 작았는데 이는 ionomer 의 고무탄성율이 보다 큰 데 기인한 것으로 해석하였다. 나아가 재료의 형상기억거동은 기 본적으로 탄성율의 온도의존성에 크게 의존함을 알수있었다.

• Journal of the Korean Society for Heat Treatment
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• v.15 no.1
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• pp.9-15
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• 2002

Deformation behavior of nickel-rich Ti-51.5at.%Ni single crystals was investigated over a wide range of temperatures(77 to 440K) and strain levels(up to 9%) in compression. These alloys combined superior strength with wide range of pseudoelasticity temperature interval(~200K). The slip deformation in [001] orientation did not occur due to the prevailing slip system, and consequently, exhibited pseudoelastic deformation at temperatures ranging from 77 to 283K and 273 to 440K for the solutionized and over-aged cases, respectively. The critical transformation stress levels were in the range of 800 to 1800MPa for the solutionized case, and 200 to 1000MPa for the over-aged case depending on the temperature and specimen orientation. These stress levels are considerably higher compared to these class of alloys having lower Ni contents. The maximum transformation strains, measured from incremental straining experiments in compression, were lower compared to the phenomenological theory with Type II twinning. A compound twinning model depending on the successive austenite(B2) to intermediate phase(R) to martensite(B19') transformation predicts lower transformation strains compared to the Type II twinning case.

• Structural Engineering and Mechanics
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• v.22 no.5
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• pp.563-574
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• 2006

This paper studies mechanical behavior of the superelastic shape memory alloy (SMA) rods in terms of local deformations and time via tensile loading-unloading cycles for both ends fixed end constraints. Besides the unique stress induced martensitic transformation (SIMT), SMA's time dependent behavior when it is in mixed-phase condition upon loading and unloading, also need careful attention with a view of investigating the local deformation of the structural elements made of the same material. With this perspective, the so-called stress-relaxation tests have been performed to demonstrate and investigate the local strains-total strains relationships with time, particularly, during the forward SIMT. Some remarkable phenomena have been observed pertaining to SIMT, which are absent in traditional materials and those unique phenomena have been explained qualitatively. For example, at the stopped loading conditions the two ends (fixed end and moving end of the tensile testing machine) were in fixed positions. So that there was no axial overall deformation of the specimen but some notable increase in the axial local deformation was shown by the extensometer placed at the middle of the SMA specimen. It should be noted that this peculiar behavior termed as 'inertia driven SIMT' occurs only when the loading was stopped at mixed phase condition. Besides this relaxation test for the SMA specimens, the same is performed for the mild steel (MS) specimens under similar test conditions. The MS specimens, however, show no unusual increase of local strains during the stress relaxation tests.