Benjamin K. Henderson

Pseudoelastic SMA Spring Elements for Passive Vibration Isolation: Part II – Simulations and Experimental Correlations

In Part II of this two-part study, system simulations and experimental correlations of a Shape Memory Alloy (SMA) based vibration isolation device (briefly described in Part I) has been presented. This device consists of layers of preconstrained SMA tubes undergoing pseudoelastic transformations under transverse dynamical loading. In Part II, detailed description of the prototype vibration isolation device, its experimental setup, and actual experimental test results are presented. An extensive parametric study has been conducted on a nonlinear hysteretic dynamical system, representing this vibration isolation device utilizing a physically based simplified SMA model and a Preisach model (an empirical model based on system identification) developed in Part I. Both the physically based simplified SMA model and the modified Preisach model have been utilized to perform experimental correlations with the results obtained from actual testing of the device. Based on the investigations, it has been shown that variable damping and tunable isolation response are major benefits of SMA pseudoelasticity. Correlation of numerical simulations and experimental results has shown that large amplitude displacements causing phase transformations of SMA components present in such a device are necessary for effective reduction in the transmissibility of such dynamical systems. It has also been shown that SMA-based devices can overcome performance trade-offs inherent in typical softening spring-damper vibration isolation systems. In terms of numerically predicting the experimental results, it has been shown that the Preisach model gave relatively accurate results due to better modeling of the actual SMA tube behavior. However, for a generic parametric study, the physically based simplified SMA model has been found to be more useful as it is motivated from the constitutive response of SMAs and hence, could easily incorporate different changes in system conditions.

PSEUDOELASTIC SMA SPRING ELEMENTS FOR PASSIVE VIBRATION ISOLATION, PART I: MODELING

In this work, the effect of pseudoelastic response of shape memory alloys (SMAs) on passive vibration isolation has been investigated. This study has been conducted by developing, modeling, and experimentally validating a SMA-based vibration isolation device. This device consists of layers of preconstrained SMA tubes undergoing pseudoelastic transformations under transverse dynamic loading. These SMA tubes are referred to as SMA spring elements in this study. To accurately model the nonlinear hysteretic response of SMA tubes present in this device, at first a Preisach model (an empirical model based on system identification) has been adapted to represent the structural response of a single SMA tube. The modified Preisach model has then been utilized to model the SMA-based vibration isolation device. Since this device also represents a nonlinear hysteretic dynamical system, a physically based simplified SMA model suitable for performing extensive parametric studies on such dynamical systems has also been developed. Both the simplified SMA model and the Preisach model have been used to perform experimental correlations with the results obtained from actual testing of the device. Based on the studies conducted, it has been shown that SMA based vibration isolation devices can overcome performance trade-offs inherent in typical softening spring-damper vibration isolation systems. This work is presented as a two-part paper. Part I of this study presents the modification of the Preisach model for representing SMA pseudoelastic tube response together with the implemented identification methodology. Part I also presents the development of a physically based simplified SMA model followed by model comparisons with the actual tube response. Part II of this work covers extensive parametric study of a pseudoelastic SMA spring-mass system using both models developed in Part I. Part II also presents numerical simulations of a dynamic system based on the prototype device, results of actual testing of the device and correlations of the experimental cases with the model predictions.

Development of a satellite structural architecture for operationally responsive space

The Air Force Research Laboratory/Space Vehicles Directorate (AFRL/RV) is developing a satellite structural architecture in support of the Department of Defenses Operationally Responsive Space (ORS) initiative. Such a structural architecture must enable rapid Assembly, Integration, and Test (AI&T) of the satellite, accommodate multiple configurations (to include structural configurations, components, and payloads), and incorporate structurally integrated thermal management and electronics, while providing sufficient strength, stiffness, and alignment accuracy. The chosen approach will allow a wide range of satellite structures to be assembled from a relatively small set of structural components. This paper details the efforts of AFRL, and its contractors, to develop the technology necessary to realize these goals.

Evacuated enclosure mounted acoustic actuator and passive attenuator

This invention presents a novel means to passively achieve a compact moving-coil actuator with a very low natural frequency. The diaphragm and voice coil are mounted in a sealed enclosure from which the air is partially or completely evacuated. This reduces the air spring effect. The diaphragm is supported by a non-linear, buckling, or collapsible support apparatus. By taking advantage of the non-linear stiffness properties of such structures, the stiffness of the actuator can be designed to be small at the operating point, which when combined with the moving mass, yields a low natural frequency.

Development of an acoustic actuator for launch vehicle noise reduction

In many active noise control applications, it is necessary that acoustic actuators be mounted in small enclosures due to volume constraints and in order to remain unobtrusive. However, the air spring of the enclosure is detrimental to the low-frequency performance of the actuator. For launch vehicle noise control applications, mass and volume constraints are very limiting, but the low-frequency performance of the actuator is critical. This work presents a novel approach that uses a nonlinear buckling suspension system and partial evacuation of the air within the enclosure to yield a compact, sealed acoustic driver that exhibits a very low natural frequency. Linear models of the device are presented and numerical simulations are given to illustrate the advantages of this design concept. An experimental prototype was built and measurements indicate that this design can significantly improve the low-frequency response of compact acoustic actuators.

Structural health monitoring: an enabler for responsive satellites

The Air Force Research Laboratory/Space Vehicles Directorate (AFRL/RV) is developing Structural Health Monitoring (SHM) technologies in support of the Department of Defenses Operationally Responsive Space (ORS) initiative. Such technologies will significantly reduce the amount of time and effort required to assess a satellites structural surety. Although SHM development efforts abound, ORS drives unique requirements on the development of these SHM systems. This paper describes several technology development efforts, aimed at solving those technical issues unique to an ORS-focused SHM system, as well as how the SHM system could be implemented within the structural verification process of a Responsive satellite.

Vibro‐acoustic launch protection experiment (VALPE)

Launch acoustic and vibration loads have the potential to damage sensitive payloads within a payload fairing, often requiring more structural mass to withstand these loads than would otherwise be necessary to survive launch. Experiments demonstrating several vibro‐acoustic mitigation technologies developed by AFRL/VS and its contractors flew on the Vibro‐Acoustic Launch Protection Experiment 2 (VALPE‐2) aboard a Terrier‐Improved Orion sounding rocket from Wallops Island Flight Facility in August 2003. Flight data collected in November 2002 from a nearly identical launch (VALPE‐1) was used to characterize the fairing environment for comparison. Preparations for the flight experiments are discussed along with the performance of the various experiments in flight. The several experiments include an Adaptive Vibro‐Acoustic Device (AVAD) to mitigate acoustic loads, an active/passive hybrid vibration isolation system using voice‐coil actuation and a ShockRing passive component, a voice‐coil regenerative electron...

Sensing capabilities of ionic polymer-metal composites

This paper presents a brief description and testing results of Ionic Polymer-Metal Composites (IPMCs) as dynamic sensors. As previously noted a strip of IPMC can exhibit large dynamic deformation if placed in a time varying electric field. Conversely, dynamic deformation of such ionic polymers produces dynamic electric fields. The underlying principle of such a mechanoelectric effect in IPMC can be explained by the linear irreversible thermodynamics in which ion and solvent transport are the fluxes and electric field and solvent pressure gradient are the forces. Important parameters include the material conductance and the permeability.

Parametric Study and Experimental Correlation of an SMA Based Damping and Passive Vibration Isolation Device

In this work, the effect of pseudoelastic response of shape memory alloys (SMAs) on damping and passive vibration isolation will be presented. This study has been conducted by developing and utilizing a shape memory alloy (SMA) model (a physically based SMA model) to perform extensive parametric studies on a non-linear hysteretic dynamic system, representing an actual SMA damping and passive vibration isolation prototype device. The prototype device consists of SMA tubes undergoing pseudoelastic transformations under transverse loading. To accurately model the non-linear hysteretic response of SMA tubes present in the prototype device, a Preisach model (an empirical model based on system identification) has also been modified to simulate the response of the prototype device. Both the simplified SMA model and the Preisach model have been utilized to perform experimental correlations with the results obtained from actual testing of the prototype device. The investigations show that variable damping and tunable isolation response are major benefits of SMA pseudoelasticity. Correlation of numerical simulations and experimental results has shown that large amplitude displacements causing phase transformations of SMA components are necessary for an SMA based vibration isolation device to be effective in reducing the transmissibility of a dynamic system. It has also been shown that SMA based devices can overcome performance trade-offs inherent in a typical softening spring-damper vibration isolation system. In terms of modeling, the Preisach model gave relatively accurate results due to close proximity in predicting actual SMA component behavior. However, for a generic parametric study, the simplified SMA model has been found to be more useful as it is motivated from the constitutive response of SMAs and hence, could easily incorporate different changes in system conditions.Copyright

Passive magneto-rheological vibration isolation apparatus using a shielding sleeve

A damper containing magneto-rheological (“MR”) fluid and a plunger lies between and is mechanically coupled both to a fixture and a vibration source. The plunger has a head immersed in the MR fluid. Annular magnets circumscribe the damper and produce a magnetic field surrounding the damper. A tubular shielding sleeve composed of magnetically impermeable material surrounds a portion of the damper. The sleeve is mechanically coupled both to the fixture and the vibration source by springs, and can translate relative to the damper to affect the strength of the magnetic field acting on the MR fluid surrounding the plunger head. The sleeve oscillates responsive to vibration of the vibration source and controls the viscosity of the MR fluid surrounding the plunger head in proportion to the amplitude of the sleeves oscillation. The resonant frequency of the sleeve is adjusted to approximate the fundamental resonance of the fixture.