Sharif Digital Repository

Most devices based on shape memory alloys experience both finite deformations and non-proportional loading conditions in engineering applications. This motivates the development of constitutive models considering finite strain as well as martensite variant reorientation. To this end, in the present article, based on the principles of continuum thermodynamics with internal variables, a three-dimensional finite strain phenomenological constitutive model is proposed taking its basis from the recent model in the small strain regime proposed by Panico and Brinson (J Mech Phys Solids 55:2491-2511, 2007). In the finite strain constitutive model derivation, a multiplicative decomposition of the... 

Results of recent studies on the effect of heat treatment after cold rolling on mechanical properties and transformation temperatures of the cast 52Ni48Ti alloys are described. It is seen that stress-induced martensite is formed when both the as-rolled and the low-temperature (≤400 °C) heat-treated samples are strained. Martensite reorientation due to the stress action occurs in samples heat treated at 500 °C and higher. Optimum recovery occurs below 600 °C resulting in hardness reduction. Recrystallization starts at 600 °C resulting in parent phase yield stress enhancement. Yield stress starts to decrease when grain growth and order-disorder transformation both occur above 700 °C. © 2006... 

This paper presents a three-dimensional phenomenological constitutive model for magnetic shape memory alloys (MSMAs), developed within the framework of irreversible continuum thermodynamics. To this end, a proper set of internal variables is introduced to reflect the microstructural consequences on the material macroscopic behavior. Moreover, a stress-dependent thermodynamic force threshold for variant reorientation is introduced which improves the model accuracy. Preassumed kinetic equations for magnetic domain volume fractions, decoupled equations for magnetization unit vectors and appropriate presentation of the limit function for martensite variant reorientation lead to a simple... 

This paper presents a new phenomenological constitutive model for shape memory alloys, developed within the framework of irreversible thermodynamics and based on a scalar and a tensorial internal variable. In particular, the model uses a measure of the amount of stress-induced martensite as scalar internal variable and the preferred direction of variants as independent tensorial internal variable. Using this approach, it is possible to account for variant reorientation and for the effects of multiaxial non-proportional loadings in a more accurate form than previously done. In particular, we propose a model that has the property of completely decoupling the pure reorientation mechanism from... 

This paper is focused on presenting an accurate framework to describe frequency-dependent energy harvesting via magnetic shape memory alloys (MSMAs). Modeling strategy incorporates the phenomenological constitutive model developed formerly together with the magnetic diffusion equation. A hyperbolic hardening function is employed to define reorientation-induced strain hardening in the material, and the diffusion equation is used to add dynamic effects to the model. The MSMA prismatic specimen is surrounded by a pickup coil, and the induced voltage during martensite-variant reorientation is investigated with the help of Faraday's law of magnetic field induction. It has been shown that, in... 

This paper studies the output voltage from a novel inertial energy harvester using magnetic shape memory alloys (MSMAs). The MSMA elements are attached to the root of a cantilever beam by means of two steps. In order to get electrical voltage, two coils are wound around the MSMAs and a shock load is applied to a tip mass at the end of the beam to have vibration in it. The beam vibration causes strain in the MSMAs along their longitudinal directions and as a result the magnetic flux alters in the coils. The change of magnetic flux in the surrounding coil produces an AC voltage. In order to predict the output voltage, the nonlinear governing equations of beam motion based on Euler-Bernoulli... 

In this paper, an alternative way of harvesting energy from ambient vibration is investigated through proposing a novel inertial energy harvester using magnetic shape memory alloys (MSMAs). To this end, a clamped-clamped beam is coupled with MSMA units which are attached to its roots. A shock load is applied to a proof mass in the middle of the beam. The beam vibration causes longitudinal strain in the MSMAs and as a result the magnetic flux alters in the coils wounding around the MSMA units and produce an AC voltage. To have a reversible strain in MSMAs, a bias magnetic field is applied in transverse direction of the MSMA units. The large scale vibration of Euler-Bernoulli beam is modeled... 

In this paper, a common energy harvester is investigated which uses a specimen of magnetic shape memory alloy (MSMA). The aim of this study is to improve system performance and to evaluate the magneto-mechanical loading on the MSMA material. Since demagnetization effect is not included in the employed original MSMA model, a method to incorporate this effect is proposed which has a good performance for the specific magneto-mechanical loading of this problem. In order to decrease the need for bias magnetic field and increase system efficiency, a new return mechanism for the MSMA specimen is proposed. The results indicate that the maximum harvested power from the improved system is obtained at...