• Smart Structures and Systems
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• v.25 no.2
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• pp.241-254
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• 2020

Using confined shape memory alloy (SMA) bar or plate, this study proposes an innovative self-centering damper. The damper is essentially properly machined SMA core, i.e., bar or plate, that encased in buckling-restrained device. To prove the design concept, cyclic loading tests were carried out. According to the test results, the damper exhibited desired flag-shape hysteretic behaviors upon both tension and compression actions, although asymmetric behavior is noted. Based on the experimental data, the hysteretic parameters that interested by seismic applications, such as the strength, stiffness, equivalent damping ratio and recentering capacity, are quantified. Processed in the Matlab/Simulink environment, a preliminary evaluation of the seismic control effect for this damper was conducted. The proposed damper was placed at the first story of a multi-story frame and then the original and controlled structures were subjected to earthquake excitations. The numerical outcome indicated the damper is effective in controlling seismic deformation demands. Besides, a companion SMA damper which represents a popular type in previous studies is also introduced in the analysis to further reveal the seismic control characteristics of the newly proposed damper. In current case, it was found that although the current SMA damper shows asymmetric tension-compression behavior, it successfully contributes comparable seismic control effect as those having symmetrical cyclic behavior. Additionally, the proposed damper even shows better global performance in controlling acceleration demands. Thus, this paper reduces the concern of using SMA dampers with asymmetric cyclic behavior to a certain degree.

• 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.

• Journal of Korea Foundry Society
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• v.18 no.6
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• pp.534-540
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• 1998

6061Al-matrix composite with TiNi shape memory fiber as reinforcement has been fabricated by Permanent Mold Casting to investigate the mechanical properties of the smart composites. The composites have showed good interface bonding as a result of the analysis of SEM and EDX. The smartness of composite is given due to the shape memory effect of the TiNi fiber which generates compressive residual stresses in the matrix material when heated after being prestrained. The tensile strength of the composites was tested at temperatures between $90^{\circ}C$ and room temperature with increasing amount of pre-strain, and it showed that the tensile strength at $90^{\circ}C$ was higher than that of the room temperature. Especially, the tensile strength of the composite increases with increasing pre-strain. It showed that hardness of matrix was higher than that of common 6061Al alloy.

• Smart Structures and Systems
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• v.20 no.5
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• pp.595-605
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• 2017

The present article reported the thermal buckling strength of the sandwich shell panel structure and subsequent improvement of the same by embedding shape memory alloy (SMA) fibre via a general higher-order mathematical model in conjunction with finite element method. The geometrical distortion of the panel structure due to the temperature is included using Green-Lagrange strain-displacement relations. In addition, the material nonlinearity of SMA fibre due to the elevated thermal environment also incorporated in the current analysis through the marching technique. The final form of the equilibrium equation is obtained by minimising the total potential energy functional and solved computationally with the help of an original MATLAB code. The convergence and the accuracy of the developed model are demonstrated by solving similar kind of published numerical examples including the necessary input parameter. After the necessary establishment of the newly developed numerical solution, the model is extended further to examine the effect of the different structural parameters (side-to-thickness ratios, curvature ratios, core-to-face thickness ratios, volume fractions of SMA fibre and end conditions) on the buckling strength of the SMA embedded sandwich composite shell panel including the different geometrical configurations.

• Journal of Powder Materials
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• v.17 no.1
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• pp.29-35
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• 2010

We produced cylindrical porous TiNi bodies by Self-propagating High-temperature Synthesis (SHS) process, varying the heating schedule prior to ignition of a loose preform compact made from (Ti+Ni) powder mixture. To investigate the effect of the heating schedule on the behaviour of combustion wave propagation and the structure of porous TiNi shape-memory alloy (SMA) body, change of temperature in the compact during SHS process was measured as a function of time and used for determining combustion temperature and combustion wave velocity. Microstructure of produced porous TiNi SMA body was observed and the results were discussed with the combustion characteristics. From the results it was concluded that the final average pore size could be controlled either by the combustion wave velocity or by the average temperature of the preform compact prior to ignition.

• Computers and Concrete
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• v.25 no.4
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• pp.293-302
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• 2020

Connections play a significant role in strength of structures against earthquake-induced loads. According to the post-seismic reports, connection failure is a cause of overall failure in reinforced concrete (RC) structures. Connection failure results in a sudden increase in inter-story drift, followed by early and progressive failure across the entire structure. This article investigated the cyclic performance and behavioral improvement of shape-memory alloy-based connections (SMA-based connections). The novelty of the present work is focused on the effect of shape memory alloy bars is damage reduction, strain recoverability, and cracking distribution of the stated material in RC moment frames under seismic loads using 3D nonlinear static analyses. The present numerical study was verified using two experimental connections. Then, the performance of connections was studied using 14 models with different reinforcement details on a scale of 3:4. The response parameters under study included moment-rotation, secant stiffness, energy dissipation, strain of bar, and moment-curvature of the connection. The connections were simulated using LS-DYNA environment. The models with longitudinal SMA-based bars, as the main bars, could eliminate residual plastic rotations and thus reduce the demand for post-earthquake structural repairs. The flag-shaped stress-strain curve of SMA-based materials resulted in a very slight residual drift in such connections.

• Earthquakes and Structures
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• v.23 no.3
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• pp.221-229
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• 2022

The external post-tension technique is one of the best strengthening methods for reinforcement and improvement of the various steel structures and substructure components such as beams. In the present work, the load carrying capacity of the post-tensioned tapered steel beams with external shape memory alloy (SMA) tendons are studied. 3D nonlinear finite element method with ABAQUS software is used to determine the effects of the increase in the flexural strength, and the improvement of the load carrying capacity. The effect of the different parameters, such as geometrical characteristics and the post-tension force applied to the tendons are also studied in this research. The results reveal that the external post-tension with SMA tendons in comparison with the steel tendons causes a significant improvement of the loading capacity. According to this, using SMA tendon for the reinforcement of the tapered beams causes a decrease in weight of these structures and as a consequence causes economic benefits for their application. This method can be used extensively for steel beams due to low executive costs and simplicity of the operation for post-tension.

• The korean journal of orthodontics
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• v.33 no.6 s.101
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• pp.465-474
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• 2003

The great variety of commercial brands of orthodontic wires available on the market, stimulated by the so called superior wires (nickel titanium with shape memory effect and superelastic nickel titanium), makes the professional choice for a suitable and less expensive material difficult. The in vitro study of the mechanical properties of the orthodontic wires acts as an auxiliary tool for the professional. In this paper, a comparative study of mechanical properties was made, using stress strain tests for 4 types of orthodontic wires (conventional stainless steel, multistranded steel, superelastic nickel titanium and thermoactivated nickel titanium) separated into 5 groups. A series of 6 tests were tested for each group of wires. Initially, each group was tested 3 times until the wires broke. Furthermore, 3 more tests for each group were performed, stretching the wires under standardized activation loads, for a reliable comparison of their mechanical properties, during loading and unloading. 1 tests were applied to check differences among the groups. In vitro, the results suggest that regarding the mechanical properties supposedly desirable for physiological teeth movement, such as resilience, elasticity modulus, strength liberated during unloading, and the way that strength is liberated, thermoactivated nickel titanium wires, acting under mouth temperature, seems to be a good choice, fellowed by superelastic nickel titanium, multistranded stainless steel, and conventional stainless sleet. Superelasticity was demonstrated for superelastic nickel titanium wires. When at $37^{\circ}C$, thermoactivated nickel titanium wires showed shape memory effect, showing that temperature is important for enhancing the mechanical properties.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.5
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• pp.79-85
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• 2017

As the number of patients suffering from Pes Planus increases, research on a correctional insole that can cope with them is increasingly required. Therefore, the design of an insole for Pes Planus Correction was studied using the superelastic effect, which is one of the characteristics of the shape memory alloy in this paper. To design an effective insole, the effect of the contact pressure induced by the insole on the plantar fascia, which is the most important muscle in the foot structure, was evaluated. Three parameters (thickness, max. height and asymmetric ratio) were set as the main design factors of the insole, and the maximum contact pressure appearing on the plantar fascia was calculated by finite element analysis and analyzed using the Taguchi method. As a result of the analysis, it was confirmed that the contact pressure was influenced in the order of max. height, thickness, and asymmetric ratio. In addition, the contact pressure was converted to a feeling pressure that could be felt by a person, and then a safety correction range was established that would not cause any irritation to the plantar fascias, even though the correction effect could be expected. This indicates the best design for the safety correction range. The design method considering the important factors established through this study can form the basis for designing a personalized correctional insole in the future.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.67-76
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• 2020

This paper reports an experimental study to evaluate the flexural behavior of concrete beams reinforced using Fe based shape memory alloy (Fe-SMA) bars. For the experiment, a concrete beam of 200mm×300mm×2,200mm was produced, and a 4% pre-strained Fe-SMA bar was used as a tensile reinforcement. As experimental variables, type of tensile reinforcement (SD400, Fe-SMA), reinforcement ratio (0.2, 0.39, 0.59, 0.78), activation of Fe-SMA (activation, non-activation), and joint method of Fe-SMA bar (Continuous, welding, coupler) were considered. The electric resistance heating method was used to activate the Fe-SMA bar, and a current of 5A/㎟ was supplied until the specimen reached 160℃. After the upward displacement of the specimen due to the camber effect was stabilized, a three-point flexural loading experiment was performed using an actuator of 2,000 kN capacity. As a result of the experiment, it was found that the upward displacement occurred due to the camber effect as the Fe-SMA bar was activated. The specimen that activated the Fe-SMA bar had an initial crack at a higher load than the specimen that did not activate it. However, as with general prestressed concrete, the effect of the prestress by Fe-SMA activation on the ultimate state of the beam was insignificant.