Hysteresis In Shape Memory Alloys Research Articles

Effect of hysteretic properties of superelastic shape memory alloys on the seismic performance of structures

Shape memory alloys (SMAs) are characterized by unique superelastic behaviour which enables the material to recover its original shape after experiencing large deformations. This phenomenon provides ideal recentring capabilities which can be used in the passive control of structures subjected to earthquakes. However in seismic applications, the hysteretic properties of the material play an important role in determining the structural response. Research has shown that the hysteretic properties of SMAs are highly dependent on the chemical composition, the manufacturing process, and the loading strain rate. This paper focuses on investigating the effect of variability in the hysteretic properties of superelastic SMAs when used as passive control devices in structures subjected to earthquakes. The hysteretic properties of SMAs are assumed to be defined by three independent parameters. A sensitivity analysis and two case studies are conducted to examine the effect of variability of each parameter on the effectiveness of SMAs as restrainers for bridges and bracings for buildings. The outcomes of the studies show that the slope of the SMAs hysteresis has similar effect on the structural response (less than 10% in average) regardless of the type of SMA application. However, the effect of changing the hysteretic height is more pronounced in the case of SMA bracings compared to SMA restrainers. This illustrates that, in general, superelastic SMAs are relatively stable in their effectiveness in various structural applications despite the changes in their hysteretic properties. Copyright © 2006 John Wiley & Sons, Ltd.

Segmented shape memory alloy actuators using hysteresis loop control

A new approach to the design and control of shape memory alloy (SMA) actuators ispresented. SMA wires are divided into many segments and their thermal states arecontrolled individually as a group of finite state machines. Instead of driving acurrent to the entire SMA wire and controlling the wire length based on the analogstrain–temperature characteristics, the new method controls the binary state (hot or cold)of individual segments and thereby the total displacement is proportional to thelength of the heated segments, i.e. austenite phase. Although the thermomechanicalproperties of SMA are highly nonlinear and uncertain with a prominent hysteresis,segmented binary control is robust and stable, providing characteristics similarto a stepping motor. However, the heating and cooling of each segment to itsbi-stable states entail longer time and larger energy for transition. In this paper, anefficient method for improving the speed of response and power consumption isdeveloped by exploiting the inherent hysteresis of SMA. Instead of keeping theextreme temperatures continuously, the temperatures return to intermediate ‘hold’temperatures closer to room temperature but sufficient to keep constant phase.Coordination of the multitude of segments having independent thermal states allows forfaster response with little latency time even for thick SMA wires. Based on stressdependent thermomechanical characteristics, the hold temperature satisfying a givenstress margin is obtained. The new control method is implemented using thePeltier effect thermoelectric devices for selective segment-by-segment heatingand cooling. Experiments demonstrate the effectiveness of the proposed method.

Describing internal subloops due to incomplete phase transformations in shape memory alloys

The hysteretic response of shape memory alloys (SMAs) is one of their essential characteristics and is related to the martensitic phase transformation. The hysteresis loop may be observed either in stress–strain or strain–temperature curves. In brief, it is possible to say that the major (or external) hysteresis loop can be defined as the envelope of all minor (or internal) hysteresis loops, usually denoted as subloops. The macroscopic description of the SMA hysteresis loops, together with their subloops due to incomplete phase transformations, is an important aspect in the phenomenological description of the thermomechanical behavior of SMAs, being of great interest in technological applications. This contribution exploits the description of these internal subloops and employs a constitutive model previously proposed by [1,20,25]. Numerical investigations of the phenomenon are carried out to show the capability of this model to describe these inner subloops. Comparisons between numerical and experimental results show that they are in close agreement. Moreover, numerical simulations are carried out to elucidate different aspects of this hysteretic behavior.

Hysteresis in shape memory alloys. Is it always a constant?

Hysteresis in shape memory alloys. Is it always a constant?

Monotone strain-stress models for shape memory alloys hysteresis loop and pseudoelastic behaviorx

To describe the behavior of Shape Memory Alloy we use a thermomechanical model, founded on a free energy which is a convex function with respect to the strain and to the martensitic volume fraction, and a concave one with respect to the temperature. The material parameters of the model are experimentally determined.

Hysteresis in shape-memory alloys

Hysteresis in shape-memory alloys

Hysteresis in shape-memory alloys

Hysteresis in shape-memory alloys

Hysteresis in shape-memory alloys

We present an overview of hysteresis phenomena in the martensitic transformation, and their relevance in the thermomechanical behaviour of shape-memory alloys. The first part of the paper introduces the concept of hysteresis, and the related phenomena of branching, dissipation and memory. The second part deals with revising some aspects of the thermomechanical behaviour of shape-memory alloys, emphasizing the hysteretic behaviour of single crystals and polycrystals under different driving conditions. The last part of the work is dedicated to the problem of modelling hysteresis phenomena in shape-memory alloys. Our focus is on phenomenological approaches which, as shown in the paper, account for the memory properties observed in hysteretic trajectories and open the possibility of deriving a generic energy balance for systems with hysteresis.

Adaptive Hysteresis Compensation for SMA Actuators with Stress-Induced Variations in Hysteresisa

The strain-temperature hysteresis for shape memory alloy (SMA) actuators has been shown to undergo large changes according to the applied load. This paper provides an adaptive hysteresis model capable of accounting for a time-varying hysteresis, specifically SMA hysteresis under a varying applied stress. Previous research has established excellent performance, in both numerical and laboratory experiments, of the adaptive hysteresis model for actuators with fixed hysteresis. In this paper, the performance of the adaptive model when there are significant changes in the hysteresis characteristics is examined in a laboratory tracking experiment.

Preisach modeling of piezoceramic and shape memory alloy hysteresis

Smart materials such as piezoceramics, magnetostrictive materials, and shape memory alloys exhibit hysteresis, and the larger the input signal the larger the effect. Hysteresis can lead to unwanted harmonics, inaccuracy in open loop control, and instability in closed loop control. The Preisach independent domain hysteresis model has been shown to capture the major features of hysteresis arising in ferromagnetic materials. Noting the similarity between the microscopic domain kinematics that generate static hysteresis effects in ferromagnetics, piezoceramics, and shape memory alloys (SMAs), we apply the Preisach model for the hysteresis in piezoceramic and shape memory alloy materials. This paper reviews the basic properties of the Preisach model, discusses control-theoretic issues such as identification, simulation, and inversion, and presents experimental results for piezoceramic sheet actuators bonded to a flexible aluminum beam, and a Nitinol SMA wire muscle that applies a bending force to the end of a beam.

Analysis of Trigger Line Models for Shape Memory Hysteresis Based on Dynamic Testing

Trigger line models for the behaviour within the pseudoelastic hysteresis of shape memory alloys are considered in the analysis of the dynamic response of a cantilevered beam constrained by shape memory wires. Quantitative results of damping and shift in natural frequencies of the structure are presented. The results are compared to theoretical predictions of the effect of inner hysteresis loops on structural dynamics. The comparison suggests that there may be two trigger lines, one for loading and one for unloading, within the hysteresis loop.

Control of Shape Memory Alloy Hysteresis Properties by Inverse Model

The realization of a shape memory alloy (SMA) actuator has been demanded in the field of microactuator for a long time. But it is difficult to control a SMA actuator precisely because of its non-linear hysteresis properties. To compensate this hysteresis property, we propose a control system in this paper. At first, we design a model of hysteresis properties and its inverse model. Then, we propose a controller to compensate the hysteretic properties by using this inverse model. Finally, we apply this method to control SMA resistance and the usefulness of this controller was demonstrated experimentally.

Temperature Hysteresis in Shape Memory Alloys

The martensitic phase transformation which produces shape memory is connected with a hysteresis. Some of the applications of shape memory alloys require small hysteresis loops, other require large ones. It is therefore important to be able to control the size of the hysteresis. For that purpose three different methods were introduced in the present paper. Mechanical vibration narrowed the hysteresis loops in both NiTi and CuZnAl alloys up to 17%, while the width of the hysteresis loops in a NiTi alloy decreased 3 similar 4 times by addition of the third element Cu. With help of a special heat treatment a nearly hysteresis-free phase transformation occured in a Ti-51Ni(at.%) alloy. The size of the hysteresis is determined by the interfacial energies of the phase boundaries and these will be big, if the E-modulus and the lattice distortion are big.

Effect of mechanical vibration, heat treatment and ternary addition on the hysteresis in shape memory alloys

The martensitic phase transition which produces shape memory is connected with a hysteresis. Some of the applications of shape memory alloys require small hysteresis loops, other require large ones. It is therefore important to be able to control the size of the hysteresis. For that purpose three different methods were introduced in the present paper. Mechanical vibration narrowed the hysteresis loops in both NiTi and CuZnAl alloys by up to 17%, while the width of the hysteresis loops in an NiTi alloy was decreased 3 to 4 times by addition of a third element, copper. With the help of a special heat treatment a nearly hysteresis-free phase transition occurred in a Ti-51 at % Ni alloy. The size of the hysteresis is determined by the interfacial energies of the phase boundaries and these will be big, if the E-modulus and the lattic distortion are big.

A mathematical model for the hysteresis in shape memory alloys

The Preisach Model for ferromagnets is generalized and adapted for the description of the hysteretic behaviour of a polycrystalline specimen of shapememory alloys. The thermodynamical properties of the individual crystallites are described by the Landau-Devonshire free energy which contains four parameters. The corresponding quadruplets of parameters of a polycrystalline body fill a region in a four-dimensional Preisach space. A thermodynamical loading path will sweep surfaces across this region and change phases in the process. The physical problem of the response of a specimen to applied loads is thus converted into the geometrical problem of counting volumes between moving surfaces. This conversion facilitates the numerical evaluation of the effect of complicated loading paths.