A review of shape memory alloy research, applications and opportunities

This chapter introduces the finite element method (FEM) as a tool for solution of classical electromagnetic problems. Although we discuss the main points in the application of the finite element method to electromagnetic design, including formulation and implementation, those who seek deeper understanding of the finite element method should consult some of the works listed in the bibliography section.

Introduction to the Finite Element Method

Review of State of Art of Smart Structures and Integrated Systems

The mechanism of the giant unipolar strain recently observed in a lead-free piezoceramic, 0.92(Bi0.5Na0.5)TiO3-0.06BaTiO(3)-0.02(K0.5Na0.5)NbO3 [S.-T. Zhang, A. B. Kounga, E. Aulbach, H. Ehrenberg, and J. Rodel, Appl. Phys. Lett. 91, 112906 (2007) was investigated. The validity of the previously proposed mechanism that the high strain comes both from a significant volume change during the field-induced phase transition, from an antiferroelectric to a ferroelectric phase and the domain contribution from the induced ferroelectric phase was examined. Monitoring the volume changes from the simultaneously measured longitudinal and transverse strains on disk-shaped samples showed that the phase transition in this specific material does not involve any notable volume change, which indicates that there is little contribution from a volume change due to the phase transition to the total strain response. Temperature dependent hysteresis measurements on unpoled samples of a nearby ferroelectric composition, 0.93(Bi0.5Na0.5)TiO3-0.06BaTiO(3) -0.01(K0.5Na0.5)NbO3 demonstrated that the origin of the large strain is due to the presence of a nonpolar phase that brings the system back to its unpoled state once the applied electric field is removed, which leads to a large unipolar strain.

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Origin of the large strain response in (K0.5Na0.5)NbO3-modified (Bi0.5Na0.5)TiO3―BaTiO3 lead-free piezoceramics

Book reviewsComposite materials: fatigue and fracture: Edited by: H.T. Hahn ASTM STP 907, 1986 (£64.00)

In this paper, we present a nonlinear constitutive relation for magnetostrictive materials that includes nonlinear coupling effects arising between temperature/preload and magnetic field strengths. The relations are derived from thermodynamic principles using Gibbs free energy expanded in a Taylor series with only the pertinent constants included as determined from experimental evidence present in existing literature. By assuming that the magnetostrictive material is operated in a biased magnetic field and perturbing this field with a small value, relations between the nonlinear material constants and linear coefficients present in existing literature are derived. The accuracy of the nonlinear constitutive relation is evaluated by comparing experimental results obtained on a Terfenol-D rod operating under both magnetic field and stress biases with theoretical values. Results indicate that the model adequately predicts the nonlinear strain/field relations in specific regimes. The nonlinear constitutive rel...

Nonlinear Constitutive Relations for Magnetostrictive Materials with Applications to 1-D Problems

Response of piezoelectric stack actuators under combined electro-mechanical loading

This paper presents results on the electro-thermo-mechanical behavior of piezoelectric materials for use in actuator applications with an emphasis on durability performance. The objective of this study was to compare the performance of different commercially available actuator systems and to determine the properties necessary for the design of such actuator systems. Basic piezoelectric properties of five stack actuators were determined as a function of mechanical preload and temperature. Changes in these properties during ferroelectric fatigue up to 107cycles were determined from strain-field relations after a specified number of fatigue cycles. Experimental results indicate a strong dependence of piezoelectric properties and power requirements on mechanical loading conditions. Results indicate that the optimum operating conditions (i.e., mechanical preload) that will improve actuation capabilities of piezoelectric stack actuators can be determined. That is, strain output was found to increase by 60% for ...

Durability properties of piezoelectric stack actuators under combined electromechanical loading

This paper presents experimental results on thermomechanical behavior of Extrinsic Fabry-Perot Interferometric fiber optic strain sensors (EFPI-FOSS). The objective of this study was to determine the accuracy, strength characteristics, and durability properties of both bare (nonembedded) EFPI sensors, and embedded optical fiber sensors in either a neat resin or aerospace grade composite laminate. Experimental results suggest that the embedded EFPI sensors provide reliable strain measurements for values exceeding 10,000 μ∊ under static loading conditions. A major portion of this study focused on evaluating the long term tension–tension fatigue behavior of optical fiber sensors. Test data suggest the EFPI sensors provide reliable data up to 1 million cycles at fatigue strain levels below 3,000 μ∊. For fatigue strain levels above this value, failure of the fiber optic sensor was observed. While the sensor failed it did not influence the strength and fatigue life of the composite coupons. Considering the desi...

Characterization of Fiber Optic Sensors for Structural Health Monitoring

The response of five commercial piezoelectric stack actuators under electrical, mechanical, and combined electro-mechanical loading was investigated in this study. The focus was to understand the behavior of piezoelectric materials under the combined electro-mechanical loading scenario, and to determine fundamental properties important for design of actuator systems that incorporate these materials. Parameters that were evaluated include strain output, permittivity, mechanical stiffness, energy density, and coupling coefficients as a function of mechanical preload and electric field values representative of in- service conditions. Stiffness measurements indicate strong dependence on applied electric field and mechanical preload, as well as the number of mechanical cycles. For certain actuators, stiffness values change by as much as 100% depending on the operating conditions. The voltage induced strain output of some of these samples which include both PZT and PLZT compositions exceeds 2,000 microstrain for certain operating conditions (under the constant preload). Initially, the strain output is enhanced with an increase in mechanical preload and the maximum strain values are obtained when the stacks are preloaded between 4 - 6 ksi. High values of output energy density can be achieved for this operating region. Applying a higher preload has the advance effect on the stacks response since mechanical loading impedes domain wall motion reducing the overall strain output. A similar effect is observed under the combined out-of-phase electro-mechanical loading, and we have found that the highest energy density is obtained if the mechanical loading amplitude does not exceed +/- 2.5 ksi.

Milan Mitrovic

Papers

Nonlinear Constitutive Relations for Magnetostrictive Materials with Applications to 1-D Problems

Response of piezoelectric stack actuators under combined electro-mechanical loading

Durability properties of piezoelectric stack actuators under combined electromechanical loading

Characterization of Fiber Optic Sensors for Structural Health Monitoring

Electromechanical characterization of piezoelectric stack actuators