Topical Collection "Shape Memory Alloys (SMAs) for Engineering Applications"

A topical collection in Materials (ISSN 1996-1944). This collection belongs to the section "Smart Materials".

Editors

Prof. Dr. Masoud Motavalli
Website
Collection Editor
Structural Engineering Laboratory, Empa Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland
Interests: application of advanced materials (such as fiber-reinforced polymer composites and shape memory alloys in civil engineering); structural rehabilitation and repair; seismic retrofitting; large and full scale laboratory and field experiments
Special Issues and Collections in MDPI journals
Dr. Christoph Czaderski
Website
Collection Editor
Structural Engineering Laboratory, Empa Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland
Interests: strengthening of reinforced concrete with CFRP (Carbon Fibre Reinforced Polymers), prestressed CFRP, and shape Memory Alloys (SMA) for usage in building industry
Prof. Dr. Moslem Shahverdi
Website
Collection Editor
Structural Engineering Laboratory, Empa Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland
Interests: shape memory alloys, fatigue and fracture mechanics, composite materials, solid mechanics, reinforced concrete, lightweight structures, numerical simulations, and field experiments

Topical Collection Information

Dear Colleagues,

This Special Issue of Materials is dedicated to “Shape Memory Alloys (SMAs) for Engineering Applications”. We are expecting to receive papers dealing with cutting-edge issues on research and application of SMAs in structural engineering. The topics of the Special Issue include, but are not limited to:

  1. Alloy designing of SMAs for structural engineering including:
    1. Nickel-titanium-based SMAs
    2. Copper-based SMAs
    3. Iron-based SMAs
    4. Aluminum-based SMAs
  2. Applications of SMAs for structural engineering using:
    1. Damping capacity of SMAs
    2. Superelasticity of SMAs
  3. Applications in structural engineering using shape memory effect of SMAs for tensioning applications as:
    1. Coupling, Fastener
    2. Tendon
    3. Concrete reinforcement
    4. Near surface mounted reinforcement
    5. Short fibers
  4. Actuator applications of SMAs in structural engineering
  5. Active vibration control in structural engineering using SMAs
  6. Hybrid composites of shape memory alloys and polymers for structural engineering
  7. SMAs as sensors for health monitoring of structural engineering
  8. Modeling of the SMAs applications in structural engineering including
    1. Material constitutive models
    2. Structural behavior models
    3. Long term behavior models

Prof. Dr. Masoud Motavalli
Dr. Christoph Czaderski
Prof. Dr. Moslem Shahverdi
Collection Editors

Manuscript Submission Information

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Keywords

  • shape memory alloys (SMAs)
  • shape memory effect (SME)
  • superelasticity
  • modeling
  • alloy design
  • structural engineering
  • civil engineering
  • smart materials
  • external strengthening
  • structural rehabilitation
  • constitutive models
  • long term behavior

Published Papers (11 papers)

2020

Jump to: 2019, 2018

Open AccessArticle
RC Structures Strengthened by an Iron-Based Shape Memory Alloy Embedded in a Shotcrete Layer—Nonlinear Finite Element Modeling
Materials 2020, 13(23), 5504; https://doi.org/10.3390/ma13235504 - 03 Dec 2020
Abstract
Shape memory alloys (SMAs) have been widely used in civil engineering applications including active and passive control of structures, sensors and actuators and strengthening of reinforced concrete (RC) structures owing to unique features such as the shape memory effect and pseudo-elasticity. Iron-based shape [...] Read more.
Shape memory alloys (SMAs) have been widely used in civil engineering applications including active and passive control of structures, sensors and actuators and strengthening of reinforced concrete (RC) structures owing to unique features such as the shape memory effect and pseudo-elasticity. Iron-based shape memory alloys (Fe-SMAs) have become popular in recent years. Use of iron-based SMAs for strengthening RC structures has received attention in the recent decade due to the advantages it presents, that is, no ducts or anchor heads are required, friction losses do not occur and no space is needed for a hydraulic device to exert force. Accordingly, Fe-SMAs embedded in a shotcrete layer have been used for pre-stressing RC beams at Empa. The aim of this study is to present an approach to model and analyze the behavior of RC members strengthened and pre-stressed with Fe-SMA rebars embedded in a shotcrete layer. The lack of research on developing finite element models for studying the behavior of concrete structures strengthened by iron-based shape memory alloys is addressed. Three-dimensional finite element models were developed in the commercial finite element code ABAQUS, using the concrete damaged plasticity model to predict the studied beams’ load–displacement response. The results of the finite element analyses show a considerably good agreement with the experimental data in terms of the beams’ cracking load and ultimate load capacity. The effects of different strengthening parameters, including SMA rebar diameter, steel rebar diameter and pre-stressing force level on the beam behavior, were investigated based on the verified finite element models. The results were compared. The load-displacement response of an 18-m concrete girder strengthened and pre-stressed with iron-based SMA bars was examined by the developed finite element model as a case study. Full article
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Open AccessEditor’s ChoiceArticle
Embedded NiTi Wires for Improved Dynamic Thermomechanical Performance of Silicone Elastomers
Materials 2020, 13(22), 5076; https://doi.org/10.3390/ma13225076 - 11 Nov 2020
Abstract
The extraordinary properties of shape memory NiTi alloy are combined with the inherent viscoelastic behavior of a silicon elastomer. NiTi wires are incorporated in a silicon elastomer matrix. Benefits include features as electrical/thermal conductivity, reinforcement along with enhanced damping performance and flexibility. To [...] Read more.
The extraordinary properties of shape memory NiTi alloy are combined with the inherent viscoelastic behavior of a silicon elastomer. NiTi wires are incorporated in a silicon elastomer matrix. Benefits include features as electrical/thermal conductivity, reinforcement along with enhanced damping performance and flexibility. To gain more insight of this composite, a comprehensive dynamic thermomechanical analysis is performed and the temperature- as well as frequency-dependent storage modulus and the mechanical loss factor are obtained. The analyses are realized for the composite and single components. Moreover, the models to express the examined properties and their temperature along with the frequency dependencies are also presented. Full article
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Open AccessArticle
In Search of the Optimal Conditions to Process Shape Memory Alloys (NiTi) Using Fused Filament Fabrication (FFF)
Materials 2020, 13(21), 4718; https://doi.org/10.3390/ma13214718 - 22 Oct 2020
Abstract
This research was performed so as to investigate the additive manufacturing of NiTi shape memory alloys, which is associated with direct processes, such as selective laser melting. In addition to its expensive production costs, NiTi readily undergoes chemical and phase modifications, mainly as [...] Read more.
This research was performed so as to investigate the additive manufacturing of NiTi shape memory alloys, which is associated with direct processes, such as selective laser melting. In addition to its expensive production costs, NiTi readily undergoes chemical and phase modifications, mainly as a result of Ni loss during processing as a result of high temperatures. This research explores the potential usefulness of NiTi as well as its limitations using indirect additive processes, such as fused filament fabrication (FFF). The first step was to evaluate the NiTi critical powder volume content (CPVC) needed to process high-quality filaments (via extrusion). A typical 3D printer can build a selected part/system/device layer-by-layer from the filaments, followed by debinding and sintering (SDS), in order to generate a near-net-shape object. The mixing, extruding (filament), printing (shaping), debinding, and sintering steps were extensively studied in order to optimize their parameters. Moreover, for the sintering step, two main targets should be met, namely: the reduction of contamination during the process in order to avoid the formation of secondary phases, and the decrease in sintering temperature, which also contributes to reducing the production costs. This study aims to demonstrate the possibility of using FFF as an additive manufacturing technology for processing NiTi. Full article
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Open AccessArticle
Investigation of Mechanical Properties of Large Shape Memory Alloy Bars under Different Heat Treatments
Materials 2020, 13(17), 3729; https://doi.org/10.3390/ma13173729 - 24 Aug 2020
Cited by 1
Abstract
Shape memory alloys (SMAs) are a class of functional materials that possess unique thermomechanical properties, such as shape memory effect (SME), superelasticity (SE), damping, and good fatigue and corrosion resistance, which enable them to become ideal materials for applications in earthquake engineering. Numerous [...] Read more.
Shape memory alloys (SMAs) are a class of functional materials that possess unique thermomechanical properties, such as shape memory effect (SME), superelasticity (SE), damping, and good fatigue and corrosion resistance, which enable them to become ideal materials for applications in earthquake engineering. Numerous studies have shown that the mechanical properties of superelastic SMAs mainly depend on the wire form, or the relationship between the microstructure and thermally induced phase transitions. However, extremely few studies have elucidated the effects of the heat-treatment strategy, size effect of large diameters, and cyclic loading. Herein, the mechanical properties of SMA bars, such as residual strain, energy dissipation, and equivalent damping ratio, were studied with different heat-treatment strategies, cyclic loadings, and strain amplitudes; this was achieved by conducting cyclic tensile tests on SMA bars with four different diameters. The results indicate that the maximum phase transformation stress was obtained with a 14 mm SMA bar subjected to heat treatment at 400 ℃ for 15 min. The mechanical properties were relatively stable after five loading–unloading cycles, which should be considered in engineering applications. The test results provide a mechanical basis for using large SMA bars in self-centering structures in seismic regions. Full article
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Open AccessArticle
Seismic Assessment of RC Bridge Columns Retrofitted with Near-Surface Mounted Shape Memory Alloy Technique
Materials 2020, 13(7), 1701; https://doi.org/10.3390/ma13071701 - 05 Apr 2020
Cited by 2
Abstract
From past earthquakes, it has been found that the large residual displacement of bridges after seismic events could be one of the major causes of instability and serviceability disruption of the bridge. The shape memory alloy bars have the ability to reduce permanent [...] Read more.
From past earthquakes, it has been found that the large residual displacement of bridges after seismic events could be one of the major causes of instability and serviceability disruption of the bridge. The shape memory alloy bars have the ability to reduce permanent deformations of concrete structures. This paper represents a new approach for retrofitting and seismic rehabilitation of previously designed bridge columns. In this concept, the RC bridge column was divided into three zones. The first zone in the critical region of the column where the plastic hinge is possible to occur was retrofitted with near-surface mounted shape memory alloy technique and wrapped with FRP sheets. The second zone, being above the plastic hinge, was confined with Fiber-Reinforced Polymer (FRP) jacket only, and the rest of the column left without any retrofitting. For this purpose, five types of shape memory alloy bars were used. One rectangular and one circular RC bridge column was selected and retrofitted with this proposed technique. The retrofitted columns were numerically investigated under nonlinear static and lateral cyclic loading using 2D fiber element modeling in OpenSees software. The results were normalized and compared with the as-built column. The results indicated that the relative self-centering capacity of RC bridge piers retrofitted with this new approach was highly greater than that of the as-built column. In addition, enhancements in strength and ductility were observed. Full article
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Open AccessArticle
Resistance Characteristics of SMA Actuator Based on the Variable Speed Phase Transformation Constitutive Model
Materials 2020, 13(6), 1479; https://doi.org/10.3390/ma13061479 - 24 Mar 2020
Cited by 2
Abstract
The shape memory alloy (SMA)-based actuators have been increasingly used in different domains, such as automotive, aerospace, robotic and biomedical applications, for their unique properties. However, the precision control of such SMA-based actuators is still a problem. Most traditional control methods use the [...] Read more.
The shape memory alloy (SMA)-based actuators have been increasingly used in different domains, such as automotive, aerospace, robotic and biomedical applications, for their unique properties. However, the precision control of such SMA-based actuators is still a problem. Most traditional control methods use the force/displacement signals of the actuator as feedback signals, which may increase the volume and weight of the entire system due to the additional force/displacement sensors. The resistance of the SMA, as an inherent property of the actuator, is a dependent variable which varies in accordance with its macroscopic strain or stress. It can be obtained by the voltage and the current imposed on the SMA with no additional measuring devices. Therefore, using the resistance of the SMA as feedback in the closed-loop control is quite promising for lightweight SMA-driven systems. This paper investigates the resistance characteristics of the SMA actuator in its actuation process. Three factors, i.e., the resistivity, the length, and the cross-sectional area, which affect the change of resistance were analyzed. The mechanical and electrical parameters of SMA were obtained using experiments. Numerical simulations were performed by using the resistance characteristic model. The simulation results reveal the change rules of the resistance corresponding to the strain of SMA and demonstrate the possibility of using the resistance for feedback control of SMA. Full article
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Open AccessArticle
Study on the Mechanical Properties of Bionic Protection and Self-Recovery Structures
Materials 2020, 13(2), 389; https://doi.org/10.3390/ma13020389 - 15 Jan 2020
Cited by 1
Abstract
A novel protective structure, based on shrimp chela structure and the shape of odontodactylus scyllarus, has been shown to improve impact resistance and energy absorption. A finite element model of NiTi alloy with shape memory was constructed based on the basic principles of [...] Read more.
A novel protective structure, based on shrimp chela structure and the shape of odontodactylus scyllarus, has been shown to improve impact resistance and energy absorption. A finite element model of NiTi alloy with shape memory was constructed based on the basic principles of structural bionics. The protective structure utilizes NiTi alloy as the matrix, a material with many advantages including excellent compression energy absorption, reusability after unloading, and long life. The mechanical properties of the single-layer model were obtained by static crushing experiments and numerical simulations. Building upon the idea of the monolayer bionic structure design, a two-layer structure is also conceived. Both single-layer and double-layer structures have excellent compression energy absorption and self-recovery capabilities. Compared with the single-layer structure, the double-layer structure showed larger compression deformation and exhibited better energy absorption capacity. These results have important academic and practical significance for improving the impact resistance of protective armor. Our study makes it possible to repair automatic rebounds under the action of pressure load and improves the endurance and material utilization rate of other protective structures. Full article
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2019

Jump to: 2020, 2018

Open AccessArticle
Active Adjustment of Surface Accuracy for a Large Cable-Net Structure by Shape Memory Alloy
Materials 2019, 12(16), 2619; https://doi.org/10.3390/ma12162619 - 16 Aug 2019
Abstract
The high surface accuracy design of a cable-net antenna structure under the disturbance of the extremely harsh space environment requires the antenna to have good in-orbit adjustment ability for surface accuracy. A shape memory cable-net (SMC) structure is proposed in this paper and [...] Read more.
The high surface accuracy design of a cable-net antenna structure under the disturbance of the extremely harsh space environment requires the antenna to have good in-orbit adjustment ability for surface accuracy. A shape memory cable-net (SMC) structure is proposed in this paper and believed to be able to improve the in-orbit surface accuracy of the cable-net antenna. Firstly, the incremental stiffness equation of a one-dimensional bar element of the shape memory alloy (SMA) to express the relationship between the force, temperature and deformation was effectively constructed. Secondly, the finite element model of the SMC antenna structure incorporated the incremental stiffness equation of a SMA was established. Thirdly, a shape active adjustment procedure of surface accuracy based on the optimization method was presented. Finally, a numerical example of the shape memory cable net structure applied to the parabolic reflectors of space antennas was analyzed. Full article
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Open AccessArticle
Thermal Cycling Effect on Transformation Temperatures of Different Transformation Sequences in TiNi-Based Shape Memory Alloys
Materials 2019, 12(16), 2512; https://doi.org/10.3390/ma12162512 - 07 Aug 2019
Cited by 3
Abstract
In TiNi-based shape memory alloys (SMAs), the effects of thermal cycling on the transformation peak temperatures of B2 ↔ B19′, B2 ↔ R, B2 ↔ B19, B2 ↔ R ↔ B19′, and B2 ↔ B19 ↔ B19′ one-stage and two-stage transformations have been [...] Read more.
In TiNi-based shape memory alloys (SMAs), the effects of thermal cycling on the transformation peak temperatures of B2 ↔ B19′, B2 ↔ R, B2 ↔ B19, B2 ↔ R ↔ B19′, and B2 ↔ B19 ↔ B19′ one-stage and two-stage transformations have been investigated and compared. Experimental results of the differential scanning calorimeter and hardness tests indicate that the alloy’s intrinsic hardness and the shear strain, s, associated with martensitic transformation, are two important factors, due to their relation to the ease of introducing dislocations during cycling. The temperature decrease by cycling for one-stage transformation was in the order of B2 ↔ B19′ > B2 ↔ B19 > B2 ↔ R according to the orders of magnitude of their s values. This phenomenon also affected the suppression of B19 ↔ B19′ and R ↔ B19′ transformation peak temperatures in two-stage transformation. Both Ti50Ni48Fe2 and Ti48.7Ni51.3 SMAs aged at 450 °C for 4 h exhibited B2 ↔ R ↔ B19′ transformation, but the hardness of the latter was much higher than that of the former due to the precipitation hardening of the Ti3Ni4 precipitates. This causesd the decrease of the R ↔ B19′ transformation peak temperature in the Ti50Ni48Fe2 SMA to be much higher than that in Ti48.7Ni51.3 SMAs aged at 450 °C for 4 h, which directly affected the sequential B2 ↔ R transformation of Ti50Ni48Fe2 SMA in the next thermal cycle and decreased this transformation peak temperature. The Ti48Ni52 SMA aged at 600 °C for 150 h underwent B2 ↔ B19′ transformation and then B2 → R → B19′/B19′ → B2 transformation as the cycle number increased, in which the B2 ↔ R transformation peak temperature raised slightly by cycling. This characteristic is uncommon and may have resulted from the strain field around the thermal-cycled dislocations favoring the formation of the R-phase. Full article
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Open AccessArticle
Strengthening of Reinforced Concrete Beams with Externally Mounted Sequentially Activated Iron-Based Shape Memory Alloys
Materials 2019, 12(3), 345; https://doi.org/10.3390/ma12030345 - 22 Jan 2019
Cited by 5
Abstract
Iron based shape memory alloys (Fe-SMA) have recently been used as active flexural strengthening material for reinforced concrete (RC) beams. Fe-SMAs are characterized by a shape memory effect (SME) which allows the recovery of previously induced plastic deformations through heating. If these deformations [...] Read more.
Iron based shape memory alloys (Fe-SMA) have recently been used as active flexural strengthening material for reinforced concrete (RC) beams. Fe-SMAs are characterized by a shape memory effect (SME) which allows the recovery of previously induced plastic deformations through heating. If these deformations are restrained a recovery stress is generated by the SME. This recovery stress can be used to prestress a SMA applied as a strengthening material. This paper investigates the performance and the load deformation behavior of RC beams strengthened with mechanical end anchored unbonded Fe-SMA strips activated by sequentially infrared heating. The performance of a single loop loaded and a double loop loaded SMA strengthened RC beam are compared to an un-strengthened beam and a reference beam strengthened with commercially available structural steel. In these tests the SMA strengthened beam had the highest cracking load and the highest ultimate load. It is shown that the serviceability behavior of a concrete beam can be improved by a second thermal activation. The sequential heating procedure causes different temperature and stress states during activation along the SMA strip that have not been researched previously. The possible effect of this different temperature and stress states on metal lattice phase transformation is modeled and discussed. Moreover the role of the martensitic transformation during the cooling process on leveling the inhomogeneity of phase state in the overheated section is pointed out. Full article
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2018

Jump to: 2020, 2019

Open AccessArticle
The Analysis of Superelasticity and Microstructural Evolution in NiTi Single Crystals by Molecular Dynamics
Materials 2019, 12(1), 57; https://doi.org/10.3390/ma12010057 - 24 Dec 2018
Cited by 5
Abstract
Superelasticity in shape memory alloys is an important feature for actuators and medical devices. However, the function of the devices is typically limited by mechanical bandwidth and fatigue, which are dominated by the microstructures. Thus, in order to correlate the mechanical response and [...] Read more.
Superelasticity in shape memory alloys is an important feature for actuators and medical devices. However, the function of the devices is typically limited by mechanical bandwidth and fatigue, which are dominated by the microstructures. Thus, in order to correlate the mechanical response and the microstructures, the microstructural evolution in NiTi single crystals under the compression, tensile, and shearing tests is simulated by molecular dynamics (MD) in the current study. Then, the martensite variant identification method, which identifies the crystal variants/phases of each lattice based on the transformation matrix, is used to post-process the MD results. The results with the detailed information of variants and phases reveal many features that have good agreement with those reported in the literature, such as X-interfaces and the transitional orthorhombic phase between the austenite and monoclinic phases. A new twin structure consisting of diamond and wedge-shaped patterns is also discovered. The macroscopic behavior, such as stress-strain curves and the total energy profile, is linked with the distribution of dislocation and twin patterns. The results suggest that the loading cases of shear and compression allow a low critical strain for the onset of martensitic transformation and a better superelasticity behavior. Therefore, the two loading cases are suitable to apply to the NiTi actuators. The current work is expected to provide insight into the mechanical responses and design guideline for NiTi shape memory alloy actuators. Full article
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