Shape Memory Alloys (SMA) have proven to be a lightweight, low cost alternative to conventional
actuators for a number of commercial applications. Future applications will require a more complex shape
changes and a detailed understanding of the performance of more complex SMA actuators is required. The
purpose of this study is to validate engineering models and design practices for SMA beams of various
configurations for future applications. Until now, SMA actuators have been fabricated into relatively
simple beam shapes. Boeing is now fabricating beams with more complicated geometries in order to
determine their strength and shape memory characteristics. These more complicated shapes will allow for
lighter and more compact SMA actuators as well as provide more complex shape control. Some of the
geometries evaluated include vertical and horizontal I-beams, sine wave and linear wave beams, a truss,
and a beam perforated with circular holes along the length.
A total of six beams were tested; each was a complex shape made from 57% Nickel by weight with the
remainder composed of Titanium (57NiTi). Each sample was put through a number of characterization
tests. These include a 3-point bend tests to determine force/displacement properties, and thermal cycling
under a range of isobaric loads to determine actuator properties. Experimental results were then compared
to modeled results. Test results for one representative beam were used to calibrate a 3-D constitutive
model implemented in an finite element framework. It is shown that the calibrated analysis tool is accurate
in predicting the response of the other beams. Finally, the actuation work capabilities of the beams are
compared using a second round of finite element anaylysis.
In the work to be presented, vacuum plasma spray forming has been used as a process to deposit and consolidate prealloyed
NiTi and NiTiPd powders into near net shape actuators. Testing showed that excellent shape memory behavior
could be developed in the deposited materials and the investigation proved that VPS forming could be a means to
directly form a wide range of shape memory alloy components. The results of DSC characterization and actual actuation
test results will be presented demonstrating the behavior of a Nitinol 55 alloy and a higher transition temperature NiTiPd
alloy in the form of torque tube actuators that could be used in aircraft and aerospace controls.
A significant reduction in noise and improved fuel consumption can be achieved by varying the area of a commercial jet
engine's fan nozzle. A larger diameter at takeoff and approach can reduce jet velocity reducing noise. Adjusting the
diameter in cruise, to account for varying Mach number, altitude, etc, can optimize fan loading and reduce fuel
consumption. Boeing recently tested a scaled variable area jet nozzle capable of a 20% area change. Shape Memory
Alloy actuators were used to position 12 interlocking panels at the nozzle exit. A closed loop control system was used to
maintain a range of constant diameters with varying flow conditions and to vary the diameter under constant flow
conditions. Acoustic data by side line microphones and flow field measurements at several cross-sections using PIV was
collected at each condition. In this paper the variable area nozzle's design is described. The effect of the nozzle's
diameter on its acoustic performance is presented for a range of Mach numbers and mass flow rates. Flow field data is
shown including the effects of the joints between the interlocking panels.
Within the last decade, the development of compact SMA actuators has led to the design of smart structures such as the
Variable Geometry Chevron (VGC), designed by Boeing engineers. The chevrons are aerodynamic devices actuated by
SMA beam actuators and placed along the trailing edge of a jet engine to provide noise reduction. The SMA actuators
are clamped on an elastic substrate that provides a biasing force allowing repeated one-way shape memory effect under
cyclic thermal actuation. In this work, a comprehensive characterization of thermally induced fatigue behavior of nickel-rich
NiTi SMA actuators subject to different constant applied stresses is presented. The influence of various parameters
is studied in order to assess the fatigue behavior of nickel-rich NiTi, namely: two heat treatments, two heat treatment
environments, three fatigue test specimen thicknesses and four stress levels. The purpose of this thermomechanical
fatigue study is to evaluate the shape recovery stability, the influence of large applied stresses, the amount of permanent
deformation and the resulting failure mechanisms. Fatigue limits of ~ 5,000 to ~ 60,000 cycles were found for applied
stress levels ranging from 250 MPa to 100 MPa.
As the use of active structures continues to become more commercially viable, the need for accurate numerical
modeling has gained importance. A current example of such a smart structure includes the variable geometry
chevron. Future applications are also being designed, including a variable area jet engine nozzles and a torque
tube actuators for rotor blades. This work concentrates on the FEA modeling of the Ni60Ti40 (wt %) SMA used
in these applications and subsequent experimental validation. The constitutive model employed for the SMA
material accounts for the full thermomechanical response and also accounts for such aspects as variable maximum
transformation strain and smooth material hardening during transition. Model calibration is performed via
uniaxial material testing. An overview of the model and material properties is presented followed by a discussion
of the analysis results for the complex aerospace actuation applications. Comparisons to experimental validation
of the overall system response are made.
In August of 2005 The Boeing Company conducted a full-scale flight test utilizing Shape Memory Alloy (SMA)
actuators to morph an engine's fan exhaust to correlate exhaust geometry with jet noise reduction. The test was
conducted on a 777-300ER with GE-115B engines. The presence of chevrons, serrated aerodynamic surfaces mounted at
the trailing edge of the thrust reverser, have been shown to greatly reduce jet noise by encouraging advantageous mixing
of the free, and fan streams. The morphing, or Variable Geometry Chevrons (VGC), utilized compact, light weight, and
robust SMA actuators to morph the chevron shape to optimize the noise reduction or meet acoustic test objectives. The
VGC system was designed for two modes of operation. The entirely autonomous operation utilized changes in the
ambient temperature from take-off to cruise to activate the chevron shape change. It required no internal heaters, wiring,
control system, or sensing. By design this provided one tip immersion at the warmer take-off temperatures to reduce
community noise and another during the cooler cruise state for more efficient engine operation, i.e. reduced specific fuel
consumption. For the flight tests a powered mode was added where internal heaters were used to individually control the
VGC temperatures. This enabled us to vary the immersions and test a variety of chevron configurations. The flight test
demonstrated the value of SMA actuators to solve a real world aerospace problem, validated that the technology could be
safely integrated into the airplane's structure and flight system, and represented a large step forward in the realization of
SMA actuators for production applications. In this paper the authors describe the development of the actuator system, the
steps required to integrate the morphing structure into the thrust reverser, and the analysis and testing that was required
to gain approval for flight. Issues related to material strength, thermal environment, vibration, electrical power, controls,
data acquisition, and engine operability are discussed. Furthermore the authors layout a road map for the next stage of
development of SMA aerospace actuators. A detailed look at the requirements and specifications that may define a
production SMA actuator and the technology development required to meet them are presented. A path for meeting
production requirements and achieving the next level of technology readiness for both autonomous and controlled SMA
actuators is proposed. This path relies strongly on cross functional and organizational teaming including industry,
academia, and government.
An accurate measure of a Shape Memory Alloy's (SMA) transition temperatures is necessary for the development of successful SMA actuator designs. Differential Scanning Calorimetry (DSC) is used to obtain SMA transition temperatures associated with changes in alloy formulations, fabrication processes, and forming methods, and to predict an SMA's thermal characteristics when designed into an actuator. However there is little data directly correlating a material's DSC results with its performance in an actuator configuration, particularly for large-scale actuators producing high force and large displacements. In this paper the authors compare the DSC results of several NiTinol samples with the thermal performance of the same material in a rotary actuator. Data are presented for NiTinol torque tubes 14cm (5.5 in) long by 1 cm (0.4 in) in diameter. The tubes were tested over a range of loads exceeding 17 N*m (150 in-lbs) of torque, with angular displacements of more than 60 degrees, and for durations exceeding 3,500 thermal cycles. Data from various NiTinol suppliers, levels of cold work, and a range of aging temperatures is presented. The DSC data is directly compared to the strain vs. temperature hysteresis curves of the same material under various loads; both before and after extended cycling. The value of the DSC measurements as a predictor of a material's thermal characteristics in an actuator configuration is assessed.
Boeing is applying cutting edge smart material actuators to the next generation morphing technologies for aircraft. This effort has led to the Variable Geometry Chevrons (VGC), which utilize compact, light weight, and robust shape memory alloy (SMA) actuators. These actuators morph the shape of chevrons on the trailing edge of a jet engine in order to optimize acoustic and performance objectives at multiple flight conditions. We have demonstrated a technical readiness level of 7 by successfully flight testing the VGCs on a Boeing 777-300ER with GE-115B engines. In this paper we describe the VGC design, development and performance during flight test. Autonomous operation of the VGCs, which did not require a control system or aircraft power, was demonstrated. A parametric study was conducted showing the influence of VGC configurations on shockcell generated cabin noise reduction during cruise. The VGC system provided a robust test vehicle to explore chevron configurations for community and shockcell noise reduction. Most importantly, the VGC concept demonstrated an exciting capability to optimize jet nozzle performance at multiple flight conditions.
The successful and practical application of shape memory alloy (SMA) torque tube actuators has frequently been hindered by an incomplete understanding of the effects of manufacturing and processing variables, particularly when working with large-scale systems producing high force and large displacements. Recently the authors have developed data for NiTinol SMA torque tubes subjected to a variety of processes routinely encountered in everyday industrial practice, with the objective of developing a robust and reliable high-energy actuator. Data are presented for more than 25 NiTinol torque tubes 5.5" long by 0.4" in diameter. The tubes were tested over a range of steady and variable loads exceeding 150 in-lbs of torque, with angular displacements of more than 60 degrees, and for durations exceeding 10,000 thermal cycles. Each tube's performance is characterized as a function of material source, level of cold work, heat treatment, tube fabrication technique, and training regime, and the results are shown. Changes in mechanical and shape memory property were also tracked, and they are reported. Application of NiTinol characteristics to practical design and fabrication of SMA actuators meeting a wide range of angular displacement and torque requirements will also be discussed.
The Boeing Active Flow Control (AFC) System (BAFCS) is a DARPA sponsored program to develop AFC technology to achieve a significant increase in payload for rotorcraft applications such as the V-22 tiltrotor vehicle. The program includes Computational Fluid Dynamics (CFD) analysis, wind tunnel testing and development of smart material based AFC actuators. This paper will provide an overview of the program, concentrating on the development of the AFC actuators, and is an update of reference 1,2.
A laboratory study has been performed by Boeing Aerospace Electronics under the sponsorship of the Air Force to investigate the effects of contamination on the electrostatic charging phenomena of spacecraft thermal blankets for the Ulysses mission. Induced contamination by the upperstage PAM-S Star-48B motor nozzle post-burn outgassing was studied for three types of electrically conductive thermal blankets: indium-tin-oxide-coated electrodag-coated and aluminized Kapton. Blanket samples were irradiated with 50 eV electrons at temperatures ranging from 25C to -100C and contaminant deposition thicknesses ranging from 200 to 3000 A (assuming specific gravity of 1. 0). The experimental results show that the charging characteristics of all three contaminated blankets are similar. Charge accumulation was observed to be a strong function of contaminant deposition temperature and a non-linear function of primary electron flux. 1.