scholarly journals A Constitutive Model for Superelastic Shape Memory Alloys Considering the Influence of Strain Rate

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Hui Qian ◽  
Hongnan Li ◽  
Gangbing Song ◽  
Wei Guo
Keyword(s):  
Energy Dissipation ◽  
Constitutive Equation ◽  
Shape Memory Alloys ◽  
Strain Rate ◽  
Shape Memory ◽  
Functional Materials ◽  
Tensile Tests ◽  
Hysteretic Behavior ◽  
Seismic Engineering ◽  
Energy Dissipation Devices

Shape memory alloys (SMAs) are a relatively new class of functional materials, exhibiting special thermomechanical behaviors, such as shape memory effect and superelasticity, which enable their applications in seismic engineering as energy dissipation devices. This paper investigates the properties of superelastic NiTi shape memory alloys, emphasizing the influence of strain rate on superelastic behavior under various strain amplitudes by cyclic tensile tests. A novel constitutive equation based on Graesser and Cozzarelli’s model is proposed to describe the strain-rate-dependent hysteretic behavior of superelastic SMAs at different strain levels. A stress variable including the influence of strain rate is introduced into Graesser and Cozzarelli’s model. To verify the effectiveness of the proposed constitutive equation, experiments on superelastic NiTi wires with different strain rates and strain levels are conducted. Numerical simulation results based on the proposed constitutive equation and experimental results are in good agreement. The findings in this paper will assist the future design of superelastic SMA-based energy dissipation devices for seismic protection of structures.

scholarly journals Hysteretic Behavior and Ultimate Energy Dissipation Capacity of Large Diameter Bars Made of Shape Memory Alloys under Seismic Loadings

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1099
Author(s):  
González-Sanz ◽  
Galé-Lamuela ◽  
Escolano-Margarit ◽  
Benavent-Climent
Keyword(s):  
Energy Dissipation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
High Cycle Fatigue ◽  
Large Diameter ◽  
Hysteretic Behavior ◽  
Cycle Fatigue ◽  
Seismic Loadings ◽  
Energy Dissipation Capacity ◽  
Energy Dissipation Devices

Shape memory alloys in the form of bars are increasingly used to control structures under seismic loadings. This study investigates the hysteretic behavior and the ultimate energy dissipation capacity of large-diameter NiTi bars subjected to low- and high-cycle fatigue. Several specimens are subjected to quasi-static and to dynamic cyclic loading at different frequencies. The influence of the rate of loading on the shape of the hysteresis loops is analysed in terms of the amount of dissipated energy, equivalent viscous damping, variations of the loading/unloading stresses, and residual deformations. It is found that the log-log scale shows a linear relationship between the number of cycles to failure and the normalized amount of energy dissipated in one cycle, both for low- and for high-cycle fatigue. Based on the experimental results, a numerical model is proposed that consists of two springs with different restoring force characteristics (flag-shape and elastic-perfectly plastic) connected in series. The model can be used to characterize the hysteretic behavior of NiTi bars used as energy dissipation devices in advanced earthquake resistant structures. The model is validated with shake table tests conducted on a reinforced concrete structure equipped with 12.7 mm diameter NiTi bars as energy dissipation devices.

Shape Memory Alloys for Seismic Response Modification: A State-of-the-Art Review

2005 ◽  
Vol 21 (2) ◽  
pp. 569-601 ◽  
Author(s):  
John C. Wilson ◽  
Michael J. Wesolowsky
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Seismic Response ◽  
Earthquake Engineering ◽  
Materials Science ◽  
State Of The Art ◽  
High Strength ◽  
High Energy ◽  
Hysteretic Behavior ◽  
Seismic Engineering

Shape memory alloys (SMAs) are a remarkable class of metals that can offer high strength, large energy dissipation through hysteretic behavior, extraordinary strain capacity (up to 8%) with full shape recovery to zero residual strain, and a high resistance to corrosion and fatigue—aspects that are all desirable from an earthquake engineering perspective. Their various physical characteristics result from solid-solid transformation between austenite and martensite phases of the alloy that may be induced by stress or temperature. The most commercially successful SMA is a binary alloy of nickel and titanium (NiTi). Although SMAs are expensive relative to most other materials used in seismic engineering, in certain forms their capacity for high energy loss per unit volume means that comparatively small quantities can be made to be especially effective, for example when used in wire form as part of a seismic bracing system. This state-of-the-art paper presents current materials science aspects, material models, and mechanical behavior of SMAs relevant to seismic engineering, and examines the current state of design of SMA-based seismic response modification devices and their use in buildings and bridges. SMA-based devices offer promising advantages for development of next-generation seismic protection systems.

An Energy Dissipation Device Based on Shape Memory Alloys for Frame Structures

2014 ◽  
Vol 580-583 ◽  
pp. 1591-1594
Author(s):  
Yun Chen ◽  
Nai Long Zhu ◽  
Shuai Gao
Keyword(s):  
Energy Dissipation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Analytical Study ◽  
Time History ◽  
Frame Structures ◽  
Finite Element Program ◽  
History Analysis ◽  
Element Program ◽  
Energy Dissipation Devices

This paper proposes an energy dissipation device based on shape memory alloys (SMA) for frame structures. By setting anchorage device below and near the inflection point of the first storey columns, a set of force cable and energy dissipation cable using SMA are installed symmetrically in the anchorage device and the bottom of them fixed in the ground. Analytical study including the push-over and time-history analysis were investigated by ANSYS finite element program to a new CFST frame and an ordinary CFST frame. Studies have shown that the device can effectively control the structural displacement response and acceleration response, dissipating large amounts of earthquake energy. Therefore, the energy dissipation devices had a better value and prospects in engineering.

scholarly journals Effect of Crystallographic Orientation and Grain Boundaries on Martensitic Transformation and Superelastic Response of Oligocrystalline Fe–Mn–Al–Ni Shape Memory Alloys

2021 ◽  
Author(s):  
A. Bauer ◽  
M. Vollmer ◽  
T. Niendorf
Keyword(s):  
Martensitic Transformation ◽  
Grain Boundary ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Grain Boundaries ◽  
Tensile Tests ◽  
Image Correlation ◽  
Stress Concentrations ◽  
Grain Orientations ◽  
High Degree

AbstractIn situ tensile tests employing digital image correlation were conducted to study the martensitic transformation of oligocrystalline Fe–Mn–Al–Ni shape memory alloys in depth. The influence of different grain orientations, i.e., near-〈001〉 and near-〈101〉, as well as the influence of different grain boundary misorientations are in focus of the present work. The results reveal that the reversibility of the martensite strongly depends on the type of martensitic evolving, i.e., twinned or detwinned. Furthermore, it is shown that grain boundaries lead to stress concentrations and, thus, to formation of unfavored martensite variants. Moreover, some martensite plates seem to penetrate the grain boundaries resulting in a high degree of irreversibility in this area. However, after a stable microstructural configuration is established in direct vicinity of the grain boundary, the transformation begins inside the neighboring grains eventually leading to a sequential transformation of all grains involved.

Adaptive Elastic SMA Elements for Damping Applications

2013 ◽  
Author(s):  
Alexander Czechowicz ◽  
Peter Dültgen ◽  
Sven Langbein
Keyword(s):  
Boundary Conditions ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Smart Materials ◽  
Electrical Resistance ◽  
Thermal Activation ◽  
Hysteretic Behavior ◽  
Damping Function ◽  
Actual Shape ◽  
Elastic Elements

Shape memory alloys (SMA) are smart materials, which have two technical usable effects: While pseudoplastic SMA have the ability to change into a previously imprinted actual shape through the means of thermal activation, pseudoelastic SMA show a reversible mechanical elongation up to 8% at constant temperature. The transformation between the two possible material phases (austenite and martensite) shows a hysteretic behavior. As a result of these properties, SMA can be used as elastic elements with intrinsic damping function. Additionally the electrical resistance changes remarkably during the material deformation. These effects are presented in the publication in combination with potential for applications in different branches at varying boundary conditions. The focus of the presented research is concentrated on the application of elastic elements with adaptive damping function. As a proof for the potential considerations, an application example sums up this presentation.

Shape Memory Alloys Wires: From Small to Medium Diameter

2016 ◽  
Vol 101 ◽  
pp. 79-88 ◽  
Author(s):  
Vicenç Torra ◽  
Sara Casciati ◽  
Michele Vece
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Mechanical Energy ◽  
Critical Discussion ◽  
Point Of View ◽  
Hysteretic Behavior ◽  
External Temperature ◽  
Cold Temperatures ◽  
Thin Wires ◽  
Different Diameters

The use of Shape Memory Alloys in dampers devices able to reduce the wind, rain or traffic induced oscillations in stayed cables is well represented in the literature. An analysis realized on standard cables at existing facilities shows the reliable efficiency of the SMA wire in damping oscillations. Such studies also provide tools to build the SMA dampers and to account for the effects of the external temperature in the SMA. The particular study reported in this paper focuses on a critical discussion on the relation between the wire diameter and macroscopic behavior and external temperature effects. The damping requires the absorption of the mechanical energy and its conversion to heat via the action of hysteresis cycles. The study was realized on wires of different diameters. In particular, the study centers on wires of diameter 0.2, 0.5 and 2.46 mm. The flat cycles showed by the thin wires (i.e., diameter 0.2 and 0.5 mm) and the non-classical S-shaped cycles of wires of diameter 2.46 mm establish clear differences of the response under external summer-winter temperature actions. Depending of the room temperature and SMA composition, a complete flat transformation in thin wires requires stresses, in general, near 300-400 MPa. A complete transformation for an S-shaped cycle need stresses as higher as 600 MPa. The analysis of the behavior of these wires under the action of warm temperatures in summer and cold temperatures in winter, suggests that thin wires lose their pseudo-elastic state in winter. The S-shaped permits positive working in extended temperature domain and a supplementary investigation establishes that S-shaped can be increased by strain aging. The hysteretic behavior in S-shaped permits practical working under external temperatures as applications in bridges require. From a fundamental point of view, the flat cycles are coherent with the classical treatment of the SMA as a first order phase transition but the S-shaped can be considered associated to an anomaly in heat capacity.

Effect of Nitrogen Addition on TiNi Shape Memory Alloys

2020 ◽  
Vol 12 (9) ◽  
pp. 1403-1408
Author(s):  
Izaz Ur Rehman ◽  
Tae-Hyun Nam
Keyword(s):  
Mechanical Properties ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Tensile Tests ◽  
Nitrogen Addition ◽  
Ternary Alloys ◽  
X Ray Diffraction ◽  
Transformation Temperatures ◽  
Arc Melting ◽  
Type Phase

In present paper we will show how nitrogen effects microstructures, transformation temperatures, and mechanical properties of equiatomic Ti50–Ni50 and Ti-rich Ti51–Ni49 binary shape memory alloys. 0.5 at.% of nitrogen was added to prepare Ti50–Ni49.5–N0.5, and Ti51–Ni48.5–N0.5 (at.%) alloys by arc-melting. Microstructures were investigated by scanning electron microscope (SEM), phase constitutions were investigated by X-ray diffraction (XRD), transformation temperatures were investigated by differential scanning calorimeter (DSC) and mechanical properties were tested by tensile tests. Solutions treated Ti–Ni–N shape memory alloys contain TiNi matrix without nitrogen, Ti2Ni type phase containing a small amount of nitrogen and a new Ti2N type phase containing a small amount of nickel. Compared with Ti50–Ni50 and Ti51–Ni49 binary alloys, the martensitic transformation starts temperatures (Ms) of Ti50–Ni49.5–N0.5 and Ti51–Ni48.5–N0.5 ternary alloys decreased from 63.4 °C to 41.6 °C and from 85.3 °C to 79.4 °C, respectively. By adding N, fracture strain decreased and incomplete superelasticity was observed.

Micro pulling down growth of very thin shape memory alloys single crystals

2017 ◽  
Vol 10 (01) ◽  
pp. 1740003 ◽  
Author(s):  
I. López-Ferreño ◽  
J. San Juan ◽  
T. Breczewski ◽  
G. A. López ◽  
M. L. Nó
Keyword(s):  
Mechanical Properties ◽  
Shape Memory Alloys ◽  
Single Crystal ◽  
Shape Memory ◽  
Single Crystals ◽  
Functional Materials ◽  
Small Scale ◽  
Cylindrical Shape ◽  
Minimum Diameter ◽  
Wide Range

Shape memory alloys (SMAs) have attracted much attention in the last decades due to their thermo-mechanical properties such as superelasticity and shape memory effect. Among the different families of SMAs, Cu–Al–Ni alloys exhibit these properties in a wide range of temperatures including the temperature range of 100–200[Formula: see text]C, where there is a technological demand of these functional materials, and exhibit excellent behavior at small scale making them more competitive for applications in Micro Electro-Mechanical Systems (MEMS). However, polycrystalline alloys of Cu-based SMAs are very brittle so that they show their best thermo-mechanical properties in single-crystal state. Nowadays, conventional Bridgman and Czochralski methods are being applied to elaborate single-crystal rods up to a minimum diameter of 1[Formula: see text]mm, but no works have been reported for smaller diameters. With the aim of synthesizing very thin single-crystals, the Micro-Pulling Down ([Formula: see text]-PD) technique has been applied, for which the capillarity and surface tension between crucible and the melt play a critical role. The [Formula: see text]-PD method has been successfully applied to elaborate several cylindrical shape thin single-crystals down to 200[Formula: see text][Formula: see text]m in diameter. Finally, the martensitic transformation, which is responsible for the shape memory properties of these alloys, has been characterized for different single-crystals. The experimental results evidence the good quality of the grown single-crystals.

A Macromechanical Constitutive Model of Shape Memory Alloys Under Uniaxial Cyclic Loading

2012 ◽  
Vol 28 (3) ◽  
pp. 469-477 ◽  
Author(s):  
H. Lei ◽  
B. Zhou ◽  
Z. Wang ◽  
Y. Wang
Keyword(s):  
Cyclic Loading ◽  
Constitutive Model ◽  
Shape Memory Alloys ◽  
Mechanical Behavior ◽  
Shape Memory ◽  
Hysteretic Behavior ◽  
Test Results ◽  
Model Match ◽  
Number Of Cycles ◽  
The Relationship

AbstractIn this paper, the thermomechanical behavior of shape memory alloys (SMAs) subjected to uniaxial cyclic loading is investigated. To obtain experimental data, the strain-controlled cyclic loading-unloading tests are conducted at various strain-rates and temperatures. Dislocations slip and deformation twins are considered to be the main reason that causes the unique cyclic mechanical behavior of SMAs. A new variable of shape memory residual factor was introduced, which will tend to zero with the increasing of the number of cycles. Exponential form equations are established to describe the evolution of shape memory residual factor, elastic modulus and critical stress, in which the influence of strain-rate, number of cycles and temperature are taken into account. The relationship between critical stresses and temperature is modified by considering the cycling effect. A macromechanical constitutive model was constructed to predict the cyclic mechanical behavior at constant temperature. Based on the material parameters obtained from test results, the hysteretic behavior of SMAs subjected to isothermal uniaxial cyclic loading is simulated. It is shown that the numerical results of the modified model match well with the test results.

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