Use of a Ni60Ti shape memory alloy for active jet engine chevron application: II.Experimentally validated numerical analysis

Abstract

A shape memory alloy (SMA) composition ofNi60Ti40 (wt%) was chosen for the fabrication of active beam components used as cyclic actuatorsand incorporated into morphing aerospace structures. The active structure is avariable-geometry chevron (VGC) designed to reduce jet engine noise in the take-off flightregime while maintaining efficiency in the cruise regime. This two-part work addresses thetraining, characterization and derived material properties of the new nickel-rich NiTicomposition, the assessment of the actuation properties of the active beam actuator andthe accurate analysis of the VGC and its subcomponents using a model calibrated from thematerial characterization.The second part of this two-part work focuses on the numerical modeling of the jet enginechevron application, where the end goal is the accurate prediction of the VGC actuationresponse. A three-dimensional (3D) thermomechanical constitutive model is used for theanalysis and is calibrated using the axial testing results from part I. To best capture thematerial response, features of several SMA constitutive models proposed in the literatureare combined to form a new model that accounts for two material behaviors not previouslyaddressed simultaneously. These are the variation in the generated maximum actuationstrain with applied stress level and a smooth strain–temperature constitutive response atthe beginning and end of transformation. The accuracy of the modeling effort isassessed by comparing the analysis deflection predictions for a given loading pathimposed on the VGC or its subcomponents to independently obtained experimentalresults consisting of photogrammetric data. For the case of full actuation of theassembled VGC, the average error in predicted centerline deflection is less than 6%.