• Korean Journal of Materials Research
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• v.28 no.7
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• pp.381-390
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• 2018

Shape memory alloys(SMAs) have revolutionized the material engineering sciences as they exhibit exclusive features i.e. shape memory effect(SME) and super-elasticity. SMAs are those alloys that when deform return to their predeformed shape upon heating, they also restore their original shape by removing the load. Research on properties of newly advent of several types of ferrous based shape memory alloys(Fe-SMAs), shows that they have immense potential to be the counterpart of Nitinol(NiTi-SMA). These Fe-SMAs have been used and found to be effective because of their low cost, high cold workability, good weldability & excellent characteristics comparing with Nitinol(high processing cost and low cold workability) SMAs. Some of the Fe-SMAs show super-elasticity. Fe-SMAs, especially Fe-Mn-Si alloys have an immense potential for civil engineering structures because of its unique properties e.g. two-way shape memory effect, super elasticity and shape memory effect as well as due to its low cost, high elastic stiffness and wide transformation hysteresis comparative to Nitinol. Further research is being conducted on SMAs to improve and impinge better attributes by improving the material compositions, quantifying the SMA phase transition temperature etc. In this research pre-existing Fe-SMAs are categorised and collected in a tabulated form. An analysis is performed that which category is mostly available. Last 50 years data of Fe-SMA publications and US Patents is collected to show its importance in terms of increasing research on such type of alloys to invent different compositions and applications. This data is analysed as per different year groups during last 50 years and it was analysed as per whether the keywords exist in title of an article or anywhere in the article. It was found that different keywords related to Fe-SMAs/categories of Fe-SMAs, almost don't exist in the title of articles. However, these keywords related to Fe-SMAs/categories of Fe-SMAs, exist inside the article but still there are not too many publications related to Fe-SMAs/categories of Fe-SMAs.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.10-13
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• 2003

The dynamic analysis of composite plate with embedded shape memory alloys (SMAs) is studied using the finite element method. Active frequency tuning of a composite plate under electrical heating of SMAs is analyzed. The actuation of SMAs is modeled by Brinson's one-dimensional constitutive equation. The influences of the boundary conditions, the ply orientations and the pre-strains of SMA wires on the thermo-dynamic response of composite plate are discussed. It is found that the effect of SMAs on the dynamic response of composite plate is significant.

• Smart Structures and Systems
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• v.16 no.4
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• pp.641-665
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• 2015

In this paper, a simple and efficient phenomenological macroscopic one-dimensional model is proposed which is able to simulate main features of shape memory alloys (SMAs) particularly ferro-elasticity effect. The constitutive model is developed within the framework of thermodynamics of irreversible processes to simulate the one-dimensional behavior of SMAs under uniaxial simple tension-compression as well as pure torsion+/- loadings. Various functions including linear, cosine and exponential functions are introduced in a unified framework for the martensite transformation kinetics and an analytical description of constitutive equations is presented. The presented model can be used to reproduce primary aspects of SMAs including transformation/orientation of martensite phase, shape memory effect, pseudo-elasticity and in particular ferro-elasticity. Experimental results available in the open literature for uniaxial tension, torsion and bending tests are simulated to validate the present SMA model in capturing the main mechanical characteristics. Due to simplicity and accuracy, it is expected the present SMA model will be instrumental toward an accurate analysis of SMA components in various engineering structures particularly when the ferro-elasticity is obvious.

• Journal of Urban Science
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• v.7 no.1
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• pp.5-9
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• 2018

The nickel-titanium shape memory alloy (SMA), referred to as Nitinol, exhibits a superelastic effect that can be restored to its original shape even if a significant amount of deformation is applied at room temperature, without any additional heat treatment after removal of the load. Owing to these unique material characteristics, it has widely used as displacement control devices for seismic retrofitting in civil engineering fields as well as medical, electrical, electronic and mechanical fields. Contrary to ordinarty carbon steel, superelastic SMAs are very resistant to fatigue, and have force-displacement properties depending on loading speed. The change for the mechanical properties of superelastic SMAs are experimentally inviestigated in this study when loading cycle numbers and loading speeds are different. In addition, the standardized force-displacement properties of such superelastic SMAs are proposed with an aim to efficiently design the seismic retrofitting devices made of these materials.

• 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.

• Transactions of Materials Processing
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• v.20 no.5
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• pp.350-356
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• 2011

Shape memory alloys(SMAs) exhibit pseudoelastic behavior, characterized by the recovery of an original shape even after severe deformation, during loading and unloading within appropriate temperature regimes. The distinctive mechanical behavior is associated with stress-induced transformation of austenite to martensite during loading and reverse transformation to austenite upon unloading. To develop a material model for SMAs, it is imperative to consider the difference in moduli of active phases. For example, the Young’s modulus of the martensite is one-third to one half of that of the austenite. The model proposed herein is a modification of the one proposed recently by Ho[17]. The prediction of the behavior of SMAs during unloading before the onset of reverse transformation was improved by introducing a new internal state variable incorporating the variation of the elastic modulus.

• Smart Structures and Systems
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• v.5 no.5
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• pp.565-585
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• 2009

Superelastic Shape Memory Alloys (SMAs) are gaining acceptance for use as reinforcing bars in concrete structures. The seismic behaviour of concrete frames reinforced with SMAs is being assessed in this study. Two eight-storey concrete frames, one of which is reinforced with regular steel and the other with SMAs at the plastic hinge regions of beams and regular steel elsewhere, are designed and analyzed using 10 different ground motion records. Both frames are located in the highly seismic region of Western Canada and are designed and detailed according to current seismic design standards. The validation of a finite element (FE) program that was conducted previously at the element level is extended to the structure level in this paper using the results of a shake table test of a three-storey moment resisting steel RC frame. The ten accelerograms that are chosen for analyzing the designed RC frames are scaled based on the spectral ordinate at the fundamental periods of the frames. The behaviour of both frames under scaled seismic excitations is compared in terms of maximum inter-storey drift, top-storey drift, inter-storey residual drift, and residual top-storey drift. The results show that SMA-RC frames are able to recover most of its post-yield deformation, even after a strong earthquake.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.51-54
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• 2005

Shape memory alloys (SMAs) find many applications in smart composite structural systems as the active components. Their ability to provide a high force and large displacement makes them an excellent candidate for an actuator for controlling the shape of smart structures. In this paper, using a macroscopic model that captures the thermo-mechanical behaviors and the two-way shape memory effect (TWSME) of SMAs smart morphing polymeric composite shell structures like shape-changeable UAV wings is demonstrated and analyzed numerically and experimentally when subjected to various kinds of pressure loads. The controllable shapes of the morphing shells to that thin SMA strip actuator are attached are investigated depending on various phase transformation temperatures. SMA strips start to transform from the martensitic into the austenitic state upon actuation through resistive heating, simultaneously recover the prestrain, and thus cause the shell structures to deform three dimensionally. The behaviors of composite shells attached with SMA strip actuators are analyzed using the finite element methods and 3-D constitutive equations of SMAs. Several morphing composite shell structures are fabricated and their experimental shape changes depending on temperatures are compared to the numerical results. That two results show good correlations indicates the finite element analysis and 3-D constitutive equations are accurate enough to utilize them for the design of smart composite shell structures for various applications.

• International Journal of Aeronautical and Space Sciences
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• v.7 no.1
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• pp.137-147
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• 2006

In this study, shape memory alloy damper with characteristics of pseudoelastic hysteresis for helicopter rotor blades are investigated. SMAs can be available in damping augmentation of vibrating structures. SMAs show large hysteresis in the process of pseudoelastic austenite-martensite phase transformation which takes place while subjected to loading above the austenite finish temperature. Since SMAs display pseudoelastic hysteresis behavior over large strain ranges, a significant amount of energy dissipation is possible. A damper can be designed with SMA wires prestressed to a baseline level somewhere in the middle of the pseudoelastic stress range. An experimental study of the effects of pre-strain and cyclic strain amplitude as well as frequency on the damping behavior of pseudoelastic shape memory alloy wires are performed. The effects of the shape memory alloy damper on aeroelastic and ground resonance stability of helicopter are studied. In aeroelastic stability, the dynamic characteristics of blades related to pitch angle and the amplitude of lag motion for the rotor equipped with SMA damper were examined. The performance of SMA damper on ground resonance instability are presented through the frequencies and modal damping with respect to rotating speed.

• Earthquakes and Structures
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• v.23 no.5
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• pp.431-444
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• 2022

The unique thermomechanical properties of shape memory alloys (SMAs) make it a versatile material for strengthening and repairing structures. In particular, several research studies have already demonstrated the effectiveness of using the heat activated shape memory effect of nickel-titanium (Ni-Ti) based SMAs to actively confine concrete members. Despite the proven effectiveness and wide commercial availability of Ni-Ti SMAs, however, their high cost remains a major obstacle for applications in real structural engineering projects. In this study, the shape memory effect of a new, much more economical iron-based SMA (Fe-SMA) is characterized and the compressive behavior of concrete confined with Fe-SMA strips is investigated. Tests showed the Fe-SMA strips used in this study are capable of developing high levels of recovery stress and can be easily formed into hoops to provide effective active and passive confining pressure to concrete members. Compared to concrete cylinders confined with conventional carbon fiber-reinforced polymer (CFRP) composites, Fe-SMA confinement yielded significantly higher compressive deformation capacity and residual strength. Overall, the compressive behavior of Fe-SMA confined concrete was comparable to that of Ni-Ti SMA confined concrete. This study clearly shows the potential for Fe-SMA as a robust and cost-effective strengthening solution for concrete structures and opens possibilities for more practical applications.