A shape memory alloy (SMA) composition of Ni 60 Ti 40 (wt%) was chosen for the fabrication of active beam components used as cyclic actuators and incorporated into morphing aerospace structures. The active structure is a variable-geometry chevron (VGC) designed to reduce jet engine noise in the take-off flight regime while maintaining efficiency in the cruise regime. This two-part work addresses the training, characterization and derived material properties of the new nickel-rich NiTi composition, the assessment of the actuation properties of the active beam actuator and the accurate analysis of the VGC and its subcomponents using a model calibrated from the material characterization.The second part of this two-part work focuses on the numerical modeling of the jet engine chevron application, where the end goal is the accurate prediction of the VGC actuation response. A three-dimensional (3D) thermomechanical constitutive model is used for the analysis and is calibrated using the axial testing results from part I. To best capture the material response, features of several SMA constitutive models proposed in the literature are combined to form a new model that accounts for two material behaviors not previously addressed simultaneously. These are the variation in the generated maximum actuation strain with applied stress level and a smooth strain-temperature constitutive response at the beginning and end of transformation. The accuracy of the modeling effort is assessed by comparing the analysis deflection predictions for a given loading path imposed on the VGC or its subcomponents to independently obtained experimental results consisting of photogrammetric data. For the case of full actuation of the assembled VGC, the average error in predicted centerline deflection is less than 6%.

This paper addresses the modeling of hysteresis in magnetostrictive transducers. This is considered in the context of control applications which require an accurate characterization of the relation between input currents and strains output by the transducer. This relation typically exhibits signi cant nonlinearities and hysteresis due to inherent properties of magnetostrictive materials. The characterization considered here is based upon the Jiles-Atherton mean eld model for ferromagnetic hysteresis in combination with a quadratic moment rotation model for magnetostriction. As demonstrated through comparison with experimental data, the magnetization model very adequately quanti es both major and minor loops under various operating conditions. The combined model can then be used to accurately characterize output strains at moderate drive levels. The advantages to this model lie in the small number (six) of required parameters and the exibility it exhibits in a variety of operating conditions.

A shape memory alloy (SMA) with a composition of Ni 60 Ti 40 (wt%) was chosen for the fabrication of active beam elements intended for use as cyclic actuators and incorporated into a morphing aerospace structure. The active structure is a variable-geometry chevron (VGC) designed to reduce jet engine noise in the take-off flight regime while maintaining efficiency in the cruise regime. This two-part work addresses the training, characterization and derived material properties of the new nickel-rich composition, the assessment of the actuation properties of the active beam actuator and the accurate analysis of the VGC and its subcomponents using a model calibrated from the material characterization.The characterization performed in part I of this work was intended to provide quantitative information used to predict the response of SMA beam actuators of the same composition and with the same heat treatment history. Material in the form of plates was received and ASTM standard tensile testing coupons were fabricated and tested. To fully characterize the material response as an actuator, various thermomechanical experiments were performed. Properties such as actuation strain and transformation temperatures as a function of applied stress were of primary interest. Results from differential scanning calorimetry, monotonic tensile loading and constant stress thermal loading for the as-received, untrained material are first presented. These show lower transformation temperatures, higher elastic stiffnesses (60-90 GPa) and lower recoverable transformation strains (≈1.5%) when compared to equiatomic NiTi (Nitinol). Stabilization (training) cycles were applied to the tensile specimens and characterization tests were repeated for the stable (trained) material. The effects of specimen training included the saturation of cyclically generated irrecoverable plastic strains and a broadening of the thermal transformation hysteresis. A set of final derived material properties for this stable material is provided. Finally, the actuation response of a structural beam component composed of the same material given the same thermomechanical processing conditions was assessed by applying a constant bias load and a variable bias load as thermal actuation cycles were imposed.

We present a methodology based on the Néel model to build spin-lattice models for cubic crystals capable of describing magnetic properties induced by the spin-orbit coupling like magnetocrystalline anisotropy and anisotropic magnetostriction. The dipole and quadrupole terms of the Néel model are parameterized through the Bethe-Slater curve. We apply this method to develop a spin-lattice model for BCC Fe and FCC Ni, and we show that it accurately reproduces the experimental elastic tensor, magnetocrystalline anisotropy under pressure, and anisotropic magnetostrictive coefficients at zero-temperature. This work could constitute a step towards large-scale modeling of magnetoelastic phenomena.

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In order to continue the current rate of improvements in aircraft performance, aircraft and components which are continuously optimized for all flight conditions, will be needed. Toward this goal morphing-capable, adaptive structures based on shape memory alloy (SMA) technology that enable component and system-level optimization at multiple flight conditions are being developed. This paper reviews five large-scale SMA based technology programs initiated by The Boeing Company. The SAMPSON smart inlet program showed that fully integrated SMA wire bundles could provide a fighter aircraft with a variable engine inlet capability. The reconfigurable rotor blade program demonstrated the ability of highly robust, controlled 55-Nitinol tube actuators to twist a rotor blade in a spin stand test to optimize rotor aerodynamic characteristics. The variable geometry chevron (VGC) program, which was the first use of 60-Nitinol for a major aerospace application, included a flight test and static engine test of the GE90-115B engine fitted with controlled morphing chevrons that reduced noise and increased engine efficiency. The deployable rotor tab employed tube actuators to deploy and retract small fences capable of significantly reducing blade-vortex interaction generated noise on a rotorcraft. Most recently, the variable geometry fan nozzle program has built on the VGC technology to demonstrate improved jet engine performance. Continued maturation of SMA technology is needed in order to develop innovative applications and support their commercialization.

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The performance of magnetostrictive Terfenol-D is highly dependent on the state of the material and in particular on the mechanical prestress. This paper presents an experimental investigation of the effect of prestress on the dynamic performance of a Terfenol-D transducer. The effects of both prestress and magnetic bias on the near DC transducer performance are also presented. Experimental results demonstrate the sensitivity of the transducer performance in terms of strain, strain rate with applied field, and material properties to relatively small changes in initial mechanical prestress. Trends in material properties, Young' s Modulus, magnetomechanical coupling factor, permeability, dynamic strain coefficient, and mechanical quality factor with prestress and drive level are developed. In addition, the effect of magnetic bias and frequency of operation on the strain at different applied fields are examined and shown to significantly influence transducer output at a given prestress level. For the transducer as operated in this study, including the appropriate magnetic bias, both the magnetomechancial coupling and the strain coefficient are optimized with a prestress of 1 .0 to 1.25 ksi. Keywords: Terfenol-D, magnetostriction, magnetostrictive transducer, magnetomechanical effect MOTIVATIONMechanical prestress is considered one of the primary factors, along with magnetic field and temperature, which influences a magnetostrictive material's performance1. Therefore, it is of interest to the Terfenol-D designer to thoroughly investigate the effects of prestress on the performance of a Terfenol-D transducer. This will aid in the development of accurate models of transducer designs and assist in specification of a prestress optimized for a given application. In an effort to help define the investigation presented here, we pose two questions. First, what is the impact of prestress on the dynamic performance of a prototype Terfenol-D transducer? And second, will this information allow us to optimize transducer properties and performance? THE EFFECT OF PRESTRESSA compressive mechanical load or prestress on a Terfenol-D sample has several observable effects. First, the total strain capability of the material is increased by more than the initial compressive strain. Second, the ability of the material to survive high accelerations and shock conditions improves since Terfenol-D is very brittle in tension (tensile strength -28 MPa) versus compression (compressive strength -700 MPa)7. And finally, the Terfenol-D performance, as measured by the material properties, can be greatly improved or degraded. This first effect is often illustrated by the changing slope and maximum strain in the double sided strain versus applied magnetic field plots (butterflies), obtained under quasi-static conditions7. The butterflies increase in slope and saturation strain with increasing prestress until a peak is reached. Further increases in prestress result in a decrease in the slope and much larger applied fields required to reach saturation st...