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.
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.
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.
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.
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.
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.
Rules governing airport noise levels are becoming more restrictive and will soon affect the operation of commercial air traffic. Sound produced by jet engine exhaust, particularly during takeoff, is a major contributor to the community noise problem. The noise spectrum is broadband in character and is produced by turbulent mixing of primary, secondary, and ambient streams of the jet engine exhaust. As a potential approach to controlling the noise levels, piezoelectric bimorph actuators have been tailored to enhance the mixing of a single jet with its quiescent environment. The actuators are located at the edge of the nozzle and protrude into the exhaust stream. Several actuator configurations were considered to target two excitation frequencies, 250 Hz and 900 Hz, closely coupled to the naturally unstable frequencies of the mixing process. The piezoelectric actuators were constructed of 10 mil thick d31 poled wafer PZT-5A material bonded to either 10 or 20 mil thick spring steel substrates. Linear analytical beam models and NASTRAN finite element models were used to predict and assess the dynamic performance of the actuators. Experimental mechanical and electrical performance measurements were used to validate the models. A 3 inch diameter nozzle was fitted with actuators and tested in the Boeing Quiet Air Facility with the jet velocity varied from 50 to 1000 ft/s. Performance was evaluated using near-field and far-field acoustic data, flow visualization, and actuator health data. The overall sound pressure level produced from the 3 inch diameter jet illustrates the effect of both static and active actuators.
60-NiTinol (60% Nickel 40% Titanium content by weight) was developed by the US Naval Ordnance Laboratory in the 1950s as a structural form of NiTinol. Due to 60-NiTinol's extreme brittleness the application development was abandoned. Nitinol Technology Inc. successfully produced cutting instruments with this material in the early 90's. Subsequent work demonstrated that with the proper heat treatment the material exhibits a strong, stable, shape memory response. Unlike other Nitinol alloys, 60-Nitinol does not require cold work. Initial testing of this material shows that the transition temperature is a strong function of the heat treatment. Therefore the same ingot of material can produce samples with superelastic and shape memory effect. Samples with different heat treats exhibited transition temperatures varying from -55 C to +60 C. Additionally, appropriate heat treatment allows the material to exhibit extreme hardness (Rc 63) or a two-way shape memory effect. This paper provides the first study of the thermomechanical properties, including stress-strain curves and thermal cycling, of axially loaded slender 60-Nitinol samples. The samples were tested at extremely high stress level greater than 695 MPa (100 ksi) with recoverable strain of 2.5%. In addition, flexures designed with potential for aerospace applications were tested. This initial research shows that 60-Nitinol has some enticing advantages over 55 Nitinol, however further study is required.
The Boeing Active Flow Control (AFC) System is a DARPA sponsored program to develop AFC technology to achieve a significant increase in payload and/or range for rotorcraft applications such as the V-22 tiltrotor vehicle. The program includes Computational Fluid Dynamics analysis, 0.1 scale wind tunnel and 3D testing and development of smart material based AFC actuators. This paper will provide an overview of the program, concentrating on the development and testing of the AFC actuators, and is an update of references to 1 to 3.
Current research has shown that aircraft can gain significant aerodynamic performance benefits from active flow control (AFC). AFC seeks to control large scale flows by exploiting natural response triggered by small energy inputs. The principal target application is download alleviation of the V-22 Osprey under the DARPA sponsored Boeing Active Flow Control System program. One method of injecting energy into the flow over the V22 wings is to use an active vibrating surface on the passive seal between the wing and flapperon. The active surface is an oscillating cantilevered beam which injects fluid into the flow, similar to a synthetic jet, and interacts with the flow field. Two types of actuators, or flipperons, are explored. The first is a multilayer piezoelectric polyvinylidene fluoride cantilevered bender. The second is a single crystal piezoelectric (SCP)d31 poled wafer mounted on a cantilevered spring steel substrate. This paper details the development effort including fabrication, mechanical and electrical testing, and modeling for both types of actuators. Both flipperons were mounted on the passive seal between a 1/10th scale V22 wing and flapperon and the aerodynamic performance evaluated in low speed wind tunnel. The SCP flipperon demonstrated significant cruise benefits, with increase of 10 percent lift and 20 percent angle of attack capability. The PVDF flipperon provided a 16 percent drag reduction in the hover mode.
Samples of fine grain piezoelectric ceramics (less than or equal to 1 micrometers ) exhibit increased mechanical strength and improved machinability over conventional materials, which should result in actuators which have increased reliability with fewer rejected parts. The focus of the work presented here is to compare the properties of several fine grain and conventional actuators provided by TRS Ceramics. Specimens are constructed of TRS200 (a PZT-5A or DOD Type II equivalent material) and TRS600 (a PZT-5H or DOD Type VI equivalent material). All of the actuators consist of ceramic wafers bonded together with electrodes between them to form a stack. Several actuator overall dimensions and two wafer thicknesses (250 micrometers and 500 micrometers ) are investigated as well as material which has been subjected to hot isopress. The two main figures of merit in the stack actuator comparisons are free strain and blocked stress. Strain and stress loops are measured under a variety of field levels, including negative fields up to the coercive limit (full butterfly loops were not performed). Also compared are values of energy density and hysteresis in the strain, stress and electric displacement vs. field loops. Stack longevity is addressed through duration tests in which stacks are used to drive representative mechanical impedance for an extended period. Results show that fine grain stacks completed 109 continuous actuation cycles with no sign of performance degradation.
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.
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 the V-22 tiltrotor vehicle. The program includes Computational Fluid Dynamics analysis, wind tunnel testing and development of smart materials based AFC actuators. This paper will provide an overview of the program and its interrelationships, as well as concentrating on the development of the AFC actuators.
Current research has shown that aircraft can gain significant aerodynamic performance benefits by employing active flow control (AFC). One of the enabling technologies of AFC is the synthetic jet. Synthetic jets, also known as zero-net-mass flux actuators, act as bi-directional pumps injecting high momentum air into the local aerodynamic flow. Previous work has concentrated on high frequency synthetic jets based on piezoelectric active diaphragms such as Thunder actuators. Low frequency synthetic jets present a unique challenge requiring large displacements, which current technology has difficulty meeting. Boeing is investigating novel shaped low frequency synthetic jets that can modify the flow over fixed aircraft wings. This paper present the initial study of two promising active diaphragm concepts: a crescent shape and an opposing bender shape. These active diaphragms were numerically modeled utilizing the general-purpose finite element code ABAQUS. Using the ABAQUS results, the dynamic volume change within each jet was calculated and incorporated into an analytical linear Bernoulli model to predict the velocities and pressures at the nozzle. Simulations were performed to determine trends to assist in selection of prototype configurations. Prototypes of both diaphragm concepts were constructed from polyvinylidene fluoride and experimentally tested at Boeing with promising results.
A method for estimating the actuation efficiency of a structurally integrated active material is presented. A background literature search revealed many different expressions for efficiency depending upon the application and discipline of interest. Following the review of the literature, an efficiency expression was developed for a piezoelectric actuator in the frequency domain. The actuation efficiency of the piezoceramic actuator was define as the ratio of total mechanical energy imparted to the structure to total electrical energy drawn by the piezoceramic from an electrical power source. The efficiency expression is a function of the piezo electromechanical coupling coefficient, the mechanical impedance ratio of the structural to the piezoceramic material, and the frequency of operation. The developed expression was then used to analytically predict the efficiency of a single degree-of- freedom system actuated by a piezoceramic actuator. Static and quasi-static efficiency results agree with analytical results found in the literature. Dynamic analysis of the efficiency expression, however, produced unexpected and interesting results. For the given definition of efficiency, there exists a combination of material parameters and drive frequency that yield efficiencies greater than one.Further analysis provided evidence that frequency domain formulation provides that while there are instances when relatively large quantities of mechanical energy in the system exist relative to the quantity of electrical energy being drawn by the actuator, total energy is always conserved. The important result of this work was the knowledge gained in the fundamental understanding of power, energy, and efficiency as it relates to dynamic actuation of an electromechanical system. The results shown here support the concept of actuation at or near a system resonance to increase efficiency. This work is on-going; the ultimate goal of which is to develop a tool for aiding active material actuation feasibility studies by using actuation efficiency as a performance metric.
This paper presents an experimental study of the effects of varied magnetic bias, AC magnetic field amplitude and frequency on the characteristics of hysteresis loops produced in a magnetostrictive transducer. The study uses a magnetostrictive transducer designed at Iowa State University that utilizes an 11.5 cm (4.54 in) long by 1.27 cm (0.5 in) diameter cylindrical Terfenol-D rod. This transducer allows controlled variation of the following operating conditions: mechanical prestress, magnitude and frequency of AC magnetic field, and magnetic bias. By performing extensive experimental tests, material property trends can be developed for use in the optimization of transducer design parameters for different applications. For the results presented, the magnetic bias, the AC magnetic field amplitude, and the frequency of excitation were independently varied while temperature, mass load and prestress were kept constant. The minor hysteresis loops of the strain versus applied magnetic field, flux density versus applied magnetic field, and magnetization versus applied magnetic field are presented and compared. Material property trends identified from the minor loops are presented for the axial strain coefficient, permeability, susceptibility, and energy losses.
Complete models of highly-magnetostrictive Terfenol-D transducers must be able to characterize the magnetostriction upon knowledge of the impressed electrical energy. Fundamental characterization laws are not available at present, because the existing modeling techniques fail to simultaneously span all operating regimes: electric, magnetic, mechanical, and thermal, across the whole performance space of these transducers. This paper attempts to capture the essential aspects of these regimes and their interactions, i.e. those that the transducer designer is likely to encounter during design, analysis and modeling of magnetostrictive devices. The issues discussed here are the magnetization and stress states, thermal effects, magnetomechanical hysteresis, AC losses, system nonlinearities, and transducer dynamics. In addition, some of the more relevant modeling techniques that address these issues are presented and analyzed.
The theory of an electrically tunable Terfenol-D vibration absorber is developed in this paper. An overview of mangetostriction including discussion of the (Delta) E effect is presented. Experimental results showing agreement with prior art are included that demonstrate electrical control of a magnetostrictive actuator resonant frequency by varying the resonance between 1275 Hz and 1725 Hz. The tunability of the transducer resonant frequency is then implemented to achieve high bandwidth tunability in the performance of a Terfenol-D vibration absorber.
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 magnetomechanical coupling and the strain coefficient are optimized with a prestress of 1.0 to 1.25 ksi.
Modeling of magnetostrictive Terfenol-D transducer performance requires reliable data on functional trends of the magnetostrictive element's material properties under various operating conditions. A statistical study was designed to experimentally evaluate material properties of 50 Terfenol-D samples under varied mechanical loads, varied ac drive levels, magnetic bias and mechanical prestress typical of transducer applications. This approach is based on a low-signal, linear- magnetomechanical model of the test transducer, and electroacoustics theory. Statistical analysis is provided for the material properties: Young's modulus at constant applied magnetic field, linear coupling coefficient (or axial strain coefficient), magnetomechanical coupling factor, and magnetic permeability at constant strain. Functional relations between material properties and ac drive levels and loads are developed, and corresponding confidence intervals are assessed. The trends show the sensitivity of Terfenol-D material properties to the operating variables and highlight the importance of properly understanding the effects of operating conditions on transducer performance.
Quantification of Terfenol-D material properties is not readily achieved through standard stress-strain test procedures due to the sensitivity of material properties to changes in magnetic and mechanical loads. A Terfenol-D transducer can be used to measure material properties under varied operating conditions. The development of the measurement and calculation procedures used to obtain material properties is based on the model of low signal, linear magnetostriction, linear transduction equations for a transducer, and a one degree of freedom mechanical model of the transducer. Vector impedance and admittance analysis is used to determine the transducer resonant, anti-resonant, and half power point frequencies. Using these frequencies, acceleration from an accelerometer mounted on the transducer, readily measurable transducer and Terfenol-D rod parameters (mass, length, etc.), and the calculation procedures described, pertinent material properties such as the Young's moduli, permeabilities, magnetomechanical coupling factor, and the linear coupling coefficient (d33) can be determined. The subtleties of applying this theory to real world non-linear Terfenol-D operated in a transducer are addressed, including proper design and operation of a transducer to achieve circular Nyquist mobility loops. Experimental results from this method are compared with other research and the material property trends are found to be consistent.
An experimental approach is used to identify Terfenol-D material properties under magnetic bias and mechanical prestress conditions typical of transducer applications for the magnetostrictive material Terfenol-D. The approach is based on low signal transduction models, a mechanical model of the test transducer, and on the theory of vector impedance and admittance analysis. The material properties being investigated, measured directly or calculated from measured quantities, are: two Young's moduli, magnetomechanical coupling factor (or 'figure of merit' of the material), linear coupling coefficient or axial strain coefficient (d33) and two magnetic permeabilities. Electrical impedance and admittance and acceleration per unit current complex functions are measured at frequencies from 100 Hz to 5 kHz using a swept sine excitation at five applied magnetic field levels. Ten Terfenol-D samples are used in randomized performance tests to obtain the preliminary material property information that is presented. Of these ten rods, two were used in randomized performance repeatability tests for which data is also presented. These data sets demonstrate the dependence of material properties on applied magnetic field levels, and provide a preliminary assessment of the variability in material properties given known operating conditions.