Experimentally validated numerical analysis of aerostructures incorporating shape memory alloys

Hartl, Darren J.; Mooney, Jesse T.; Lagoudas, Dimitris C.; Mabe, James H.; Calkins, Frederick T.

doi:10.1117/12.776356

Cited by 5 publications

(3 citation statements)

References 16 publications

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“…17 Specifically, it relies on the Convex Cutting Plane form of the Return Mapping Algorithm. 18 The tensor-valued evolution equation for transformation strain is integrated subject to the KuhnTucker constraints on the rate-independent transformation process and further considering the elastic relations between stress, total strain, transformation strain, and temperature.…”

Section: Analysis Toolsmentioning

confidence: 99%

Analysis and optimization of improved hybrid SMA flexures for high rate actuation

Oehler

Hartl

Lagoudas

2011

Industrial and Commercial Applications of Smart Structures Technologies 2011

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The utilization of shape memory alloys (SMAs) as actuators in aerospace applications continues to show promise. These materials, when subjected to controlled changes in temperature, have the capability to provide motion while under loads that exceed thousands of times their own weight and can do so over tens of thousands of cycles. However, the rate of thermally-induced SMA transformation is significantly hindered by low thermal conductivity and latent heat effects observed in this material. The relatively long cooling times observed in SMA geometries such as beams and tubes make it difficult for controlled devices to operate with sufficiently high frequency. Therefore, the application of SMA beams as aerospace control actuators has been limited. Morphing structures such as flight control mechanisms require higher cyclic actuation frequencies than are commonly observed in SMAs, and thus have motivated the effort to increase thermal actuation rates attainable in SMA active components.This work presents an analytical study of a tapered beam actuator and discusses the possibility of using SMAs in conjunction with more conductive materials to enhance actuation performance, especially with regard to actuation cyclic frequency. The analysis involves computing the actuation work output over time of various loaded, thermally cycled active SMA beams using an accurate constitutive model implemented in a finite element framework. This set of analyses considers the solution to a transient thermomechanically coupled problem and includes the effects of latent heat of transformation on the energy balance. The study compares the effectiveness of aluminum, copper, and silver secondary material regions and their geometric configurations in altering the actuation power-to-mass ratio of the beam. An optimization scheme is used to determine the geometric distribution of each secondary material that results in the highest power-to-mass ratio. It is shown that aluminum, when optimally distributed, provides the best overall design solution of the three materials considered.

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Section: Analysis Toolsmentioning

confidence: 99%

Analysis and optimization of improved hybrid SMA flexures for high rate actuation

Oehler

Hartl

Lagoudas

2011

Industrial and Commercial Applications of Smart Structures Technologies 2011

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“…During stress-assisted TWSME, the SMA operates between a deformed and recovered configuration between the LCT and UCT, respectively, therein producing actuation stroke against external load. Generally the LCT and UCT are preferred to be less than and greater than the marteniste finish (M f ) and austenite finish (A f ) temperatures, respectively, as this leads to a complete forward and reverse transformation and maximizes stroke during each thermal cycle (Otsuka and Wayman 1998, Yuse and Kikushima 2005, Hartl et al 2008, Stebner et al 2008, Wada and Liu 2008, Grossmann et al 2009, Romano and Tannuri 2009, Lagoudas et al 2012, Saleeb et al 2013a, 2013cetc). With the above in mind, polycrystalline Ni 49.9 Ti 50.1 (nominal at%, also designated as 55NiTi) has been studied extensively with emphasis placed on the isobaric test condition (Padula et al 2014, Saleeb et al 2013aand Benafan et al 2014b.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional deformation response of a NiTi shape memory helical-coil actuator during thermomechanical cycling: experimentally validated numerical model

Dhakal

Nicholson

Saleeb

et al. 2016

Smart Mater. Struct.

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Shape memory alloy (SMA) actuators often operate under a complex state of stress for an extended number of thermomechanical cycles in many aerospace and engineering applications. Hence, it becomes important to account for multi-axial stress states and deformation characteristics (which evolve with thermomechanical cycling) when calibrating any SMA model for implementation in large-scale simulation of actuators. To this end, the present work is focused on the experimental validation of an SMA model calibrated for the transient and cyclic evolutionary behavior of shape memory Ni49.9Ti50.1, for the actuation of axially loaded helical-coil springs. The approach requires both experimental and computational aspects to appropriately assess the thermomechanical response of these multi-dimensional structures. As such, an instrumented and controlled experimental setup was assembled to obtain temperature, torque, degree of twist and extension, while controlling end constraints during heating and cooling of an SMA spring under a constant externally applied axial load. The computational component assesses the capabilities of a general, multi-axial, SMA material-modeling framework, calibrated for Ni49.9Ti50.1 with regard to its usefulness in the simulation of SMA helical-coil spring actuators. Axial extension, being the primary response, was examined on an axially-loaded spring with multiple active coils. Two different conditions of end boundary constraint were investigated in both the numerical simulations as well as the validation experiments: Case (1) where the loading end is restrained against twist (and the resulting torque measured as the secondary response) and Case (2) where the loading end is free to twist (and the degree of twist measured as the secondary response). The present study focuses on the transient and evolutionary response associated with the initial isothermal loading and the subsequent thermal cycles under applied constant axial load. The experimental results for the helical-coil actuator under two different boundary conditions are found to be within error to their counterparts in the numerical simulations. The numerical simulation and the experimental validation demonstrate similar transient and evolutionary behavior in the deformation response under the complex, inhomogeneous, multi-axial stress-state and large deformations of the helical-coil actuator. This response, although substantially different in magnitude, exhibited similar evolutionary characteristics to the simple, uniaxial, homogeneous, stress-state of the isobaric tensile tests results used for the model calibration. There was no significant difference in the axial displacement (primary response) magnitudes observed between Cases (1) and (2) for the number of cycles investigated here. The simulated secondary responses of the two cases evolved in a similar manner when compared to the experimental validation of the respective cases.

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“…NiTi-based actuators have been successfully used to bend a chevron on the trailing edge of a jet engine fairing into the exhaust stream, improving the mixing characteristics of the boundary layer and reducing engine noise (Hartl et al, 2008). The small size, relative simplicity, and ruggedness of these actuators also make them strong candidates for torsional actuators to be inserted into helicopter rotor blades that optimally change their twist profile depending on flight conditions (Mabe et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

Fusion welding of nickel–titanium and 304 stainless steel tubes: Part I: laser welding

Hahnlen

Fox

Dapino

2012

Journal of Intelligent Material Systems and Structures

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Due to their large blocking stresses, high recovery strains, and solid-state operation, nickel-titanium actuators can offer substantial weight and space savings relative to traditional electric or hydraulic systems. A challenge surrounding NiTibased actuators is integration of the NiTi components into a given system; this alloy is difficult and expensive to machine and challenging to weld to itself and structural materials. In this research, we join NiTi and 304 stainless steel tubes of 9.53 mm (0.375 in) in diameter through laser welding to create joints with weld depths up to 1.65 mm (0.065 in). By joining NiTi to a common structural material that is easily machined and readily welded to other materials, system integration is greatly improved. The joints prepared in this study were characterized through optical microscopy, hardness mapping, energy dispersive X-ray spectroscopy, mechanical testing, and analysis of the resulting fracture surfaces. The average ultimate shear strength of these joints is 429 MPa (62.2 10 3 lbf/in 2 ) and the resulting fusion zone has a maximum width of 21.9 mm with a maximum hardness of 929 HV, while a possible heat-affected zone in NiTi is limited between 1 and 2 mm over most of the weld.

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Experimentally validated numerical analysis of aerostructures incorporating shape memory alloys

Cited by 5 publications

References 16 publications

Analysis and optimization of improved hybrid SMA flexures for high rate actuation

Analysis and optimization of improved hybrid SMA flexures for high rate actuation

Three-dimensional deformation response of a NiTi shape memory helical-coil actuator during thermomechanical cycling: experimentally validated numerical model

Fusion welding of nickel–titanium and 304 stainless steel tubes: Part I: laser welding

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