Magnetic Shape Memory Alloys (MSMAs) are a type of smart material that exhibit a large amount of recoverable strain when subjected to an applied compressive stress in the presence of a magnetic field or an applied
magnetic field in the presence of a compressive stress. These macroscopic recoverable strains are the result of
the reorientation of tetragonal martensite variants. Potential applications for MSMAs include power harvesters,
sensors, and actuators. For these applications, the stress is assumed to be applied only in the axial direction,
and the magnetic field is assumed to be applied only in the transverse direction.
To realize the full potential of MSMA and optimize designs, a mathematical model that can predict the
material response under all potential loading conditions is needed. Keifer and Lagoudas [1, 2] developed a phenomenological model that characterizes the response of the MSMA to axial compressive stress and transversely
applied magnetic field based on thermodynamic principles. In this paper, a similar thermodynamic framework
is used. However, a simpler hardening function is proposed based on the observation that the reorientation
phenomenon is the same in both forward and reverse loading, as well as under both magnetic and mechanical
loading. The magnetic domains are redefined to more accurately reflect the magnetic field measured experimentally . This revised model is shown to adequately predict the magneto-mechanical response of the MSMA in
2D loading, i.e. axial compressive stress and transversely applied magnetic field.
Magnetic shape memory alloys (MSMAs) are materials that can display up to 10% recoverable strain in response to the application of a magnetic field or compressive mechanical stress. The recoverable strain depends on the magnitude of the stress and magnetic field that is applied to the material. Due to their large strains as well as fast response, MSMAs are suitable for actuation, power harvesting, and sensing applications. Broadening the range of applications for MSMAs requires an understanding of their magneto-mechanical behavior beyond 2D loading cases that have been studied to date. The response of MSMAs is primarily driven by the reorientation of martensite variants. During the reorientation process a change in material’s magnetization occurs. Using a pick-up coil (placed around, or on the side, of the specimen) one may convert this change in magnetization into an electric potential/voltage, making the material act as a power harvester. The magnitude of the output voltage depends on the number of turns of the pick-up coil, the amplitude of the reorientation strain, the magnitude and direction of the biased magnetic field, and the frequency at which the reorientation occurs. This paper presents experimental results for the material behavior under 3D loading conditions, including power harvesting data generated under such loading conditions. The 3D experimental data includes the material’s response to two compressive mechanical stresses, applied in perpendicular directions, simultaneously with the application of a magnetic field applied in the remaining orthogonal direction. The power harvesting data includes magnetic fields in multiple directions and different orientations of the pick-up coil. Results indicate that the presence of a bias magnetic field along the specimen length (i.e. the direction of application of the compressive stress) in addition to that applied normal to the specimen length, leads to an increase in the electric potential output.
The paper presents electrical and mechanical properties of structural supercapacitors and discusses limitations associated
with the approach taken for the electrical properties evaluation. The structural supercapacitors characterized in this work
had the electrodes made of carbon fiber weave, separator made of several cellulose based products, and the solid
electrolyte made as PEGDGE based polymer blend. The reported electrical properties include capacitance and leakage
resistance; the former was measured using cyclic voltammetry. Mechanical properties have been evaluated thorough
tensile and three point bending tests performed on structural supercapacitor coupons.
The results indicate that the separator material plays an important role on the electrical as well as mechanical properties
of the structural capacitor, and that Celgard 3501 used as separator leads to most benefits for both mechanical and
electrical properties. Specific capacitance and leakage resistance as high as 1.4kF/m3 and 380kΩ, respectively, were
achieved. Two types of solid polymer electrolytes were used in fabrication, with one leading to higher and more
consistent leakage resistance values at the expense of a slight decrease in specific capacitance when compared to the
other SPE formulation. The ultimate tensile strength and modulus of elasticity of the developed power storage composite
were evaluated at 466MPa and 18.9MPa, respectively. These values are 58% and 69% of the tensile strength and
modulus of elasticity values measured for a single layer composite material made with the same type of carbon fiber and
with a West System 105 epoxy instead of solid polymer electrolyte.