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%.

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.

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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.

a b s t r a c tThe mechanical and functional behaviors of a Ni-rich Ni 50.3 Ti 29.7 Hf 20 high temperature shape memory alloy were investigated through combined ex situ macroscopic experiments and in situ synchrotron X-ray diffraction. Isothermal tension and compression tests were conducted between room temperature and 260 C, while isobaric thermomechanical cycling experiments were conducted at selected stresses up to 700 MPa. Isothermal testing of the martensite phase revealed no plastic strain up to the test limit of 1 GPa and near-perfect superelastic behavior up to 3% applied strain at temperatures above the austenite finish. Excellent dimensional stability with greater than 2.5% actuation strain without accumulation of noticeable residual strains (at stresses less than or equal to À400 MPa) were observed during isobaric thermal cycling experiments. The absence of residual strain accumulation during thermomechanical cycling was confirmed by the lattice strains, determined from X-ray spectra. Even in the untrained condition, the material exhibited little or no history or path dependence in behavior, consistent with measurements of the bulk texture after thermomechanical cycling using synchrotron X-ray diffraction. Post deformation cycling revealed the limited conditions under which a slight two-way shape memory effect (TWSME) was obtained, with a maximum of 0.34% two-way shape memory strain after thermomechanical cycling under À700 MPa.Published by Elsevier Ltd.