Ralph D. Buehrle

Modeling, Fabrication, and Testing of a SMA Hybrid Composite Jet Engine Chevron Concept

This study presents a fabrication method, bench top test results, and numerical model validation for a novel adaptive jet engine chevron concept based upon embedding shape memory alloy (SMA) actuators in a composite laminate, termed a SMA hybrid composite (SMAHC). The approach for fabricating the adaptive SMAHC chevrons involves embedding prestrained Nitinol actuators on one side of the mid-plane of the composite laminate such that thermal excitation generates a thermal moment and deflects the structure. A rigorous and versatile test system for control and measurement of the chevron deflection performance is described. A recently commercialized constitutive model for SMA and SMAHC materials is used in the finite element code ABAQUS to perform nonlinear static analysis of the chevron specimens. Excellent agreement is achieved between the predicted and measured chevron deflection performance, thereby validating the numerical model and enabling detailed design of chevron prototype(s) and similar structures.

Human response to low‐intensity sonic booms heard indoors and outdoors

A house on Edwards Air Force Base, CA, was exposed to low‐intensity N‐wave sonic booms during a 3‐week test period in June 2006. The house was instrumented to measure the booms both inside and out. F‐18 aircraft were flown to achieve a variety of boom overpressures from approximately 0.01 to 0.06 psf. During 4 test days, 77 test subjects heard the booms while seated inside and outside the house. Using the Magnitude Estimation methodology and artificial reference sounds, the subjects rated the annoyance of the booms. Since the same subjects heard similar booms both inside and outside the house, comparative ratings of indoor and outdoor annoyance were obtained. Preliminary results from this test will be presented.

Energy finite‐element analysis of the NASA aluminum test‐bed cylinder

A formulation was developed in the energy finite‐element analysis (EFEA) for modeling the vibration of cylindrical structures with periodic axial and circumferential stiffeners. Appropriate power transfer coefficients are computed from the values of the propagation constants. The joint matrices of the EFEA formulation are computed based on the power transfer coefficients derived from periodic structure theory. EFEA analyses are performed for the NASA aluminum test‐bed cylinder and simulations are compared to experiments. Excitation is applied on the test‐bed cylinder by four shakers and the vibration is measured at 40 bays formed by axial and circumferential stiffeners. The EFEA results are compared successfully to test data between the 1/3 octave bands of 315 and 6300 Hz. [Work sponsored by NASA Langley Structural Acoustics Branch.]

VIBROACOUSTIC MODEL VALIDATION FOR A CURVED HONEYCOMB COMPOSITE PANEL

Finite element and boundary element models are developed to investigate the vibroacoustic response of a curved honeycomb composite sidewall panel. Results from vibroacoustic tests conducted in the NASA Langley Structural Acoustic Loads and Transmission facility are used to validate the numerical predictions. The sidewall panel is constructed from a flexible honeycomb core sandwiched between carbon fiber reinforced composite laminate face sheets. This type of construction is being used in the development of an all-composite aircraft fuselage. In contrast to conventional rib-stiffened aircraft fuselage structures, the composite panel has nominally uniform thickness resulting in a uniform distribution of mass and stiffness. Due to differences in the mass and stiffness distribution, the noise transmission mechanisms for the composite panel are expected to be substantially different from those of a conventional rib-stiffened structure. The development of accurate vibroacoustic models will aide in the understanding of the dominant noise transmission mechanisms and enable optimization studies to be performed that will determine the most beneficial noise control treatments. Finite element and boundary element models of the sidewall panel are described. Vibroacoustic response predictions are presented for forced vibration input and the results are compared with experimental data.

Design, Fabrication, and Testing of SMA Enabled Adaptive Chevrons for Jet Noise Reduction

This study presents the status and results from an effort to design, fabricate, and test an adaptive jet engine chevron concept based upon embedding shape memory alloy (SMA) actuators in a composite laminate, termed a SMA hybrid composite (SMAHC). The approach for fabricating the adaptive SMAHC chevrons involves embedding prestrained Nitinol actuators on one side of the mid-plane of the composite laminate such that thermal excitation generates a thermal moment and deflects the structure. A glass-epoxy pre-preg/Nitinol ribbon material system and a vacuum hot press consolidation approach are employed. A versatile test system for control and measurement of the chevron deflection performance is described. Projection moire interferometry (PMI) is used for global deformation measurement and infrared (IR) thermography is used for 2-D temperature measurement and feedback control. A recently commercialized constitutive model for SMA and SMAHC materials is used in the finite element code ABAQUS to perform nonlinear static analysis of the chevron prototypes. Excellent agreement is achieved between the predicted and measured chevron deflection performance, thereby validating the design tool. Although the performance results presented in this paper fall short of the requirement, the concept is proven and an approach for achieving the performance objectives is evident.

Sound Transmission Through a Curved Honeycomb Composite Panel

Composite structures are often used in aircraft because of the advantages offered by a high strength to weight ratio. However, the acoustical properties of these light and stiff structures can often be less than desirable resulting in high aircraft interior noise levels. In this paper, measurements and predictions of the transmission loss of a curved honeycomb composite panel are presented. The transmission loss predictions are validated by comparisons to measurements. An assessment of the behavior of the panel is made from the dispersion characteristics of transverse waves propagating in the panel. The speed of transverse waves propagating in the panel is found to be sonic or supersonic over the frequency range from 100 to 5000 Hz. The acoustical benefit of reducing the wave speed for transverse vibration is demonstrated.

Modal analysis of an aircraft fuselage panel using experimental and finite-element techniques

The application of electro-optic holography (EOH) for measuring the center bay vibration modes of an aircraft fuselage panel under forced excitation is presented. The requirement of free-free panel boundary conditions made the acquisition of quantitative EOH data challenging since large scale rigid body motions corrupted measurements of the high frequency vibrations of interest. Image processing routines designed to minimize effects of large scale motions were applied to successfully resurrect quantitative EOH vibrational amplitude measurements from extremely noisy data. EOH and scanning laser doppler vibrometer results have been used to validate and update finite element models of the fuselage panel. Various modeling techniques were evaluated for characterization of the panel normal modes at frequencies up to 1000 Hz. These models are briefly described, and comparisons between computational predictions and experimental measurements are presented.

Finite Element Model Calibration Approach for Ares I-X

Ares I-X is a pathfinder vehicle concept under development by NASA to demonstrate a new class of launch vehicles. Although this vehicle is essentially a shell of what the Ares I vehicle will be, efforts are underway to model and calibrate the analytical models before its maiden flight. Work reported in this document will summarize the model calibration approach used including uncertainty quantification of vehicle responses and the use of nonconventional boundary conditions during component testing. Since finite element modeling is the primary modeling tool, the calibration process uses these models, often developed by different groups, to assess model deficiencies and to update parameters to reconcile test with predictions. Data for two major component tests and the flight vehicle are presented along with the calibration results. For calibration, sensitivity analysis is conducted using Analysis of Variance (ANOVA). To reduce the computational burden associated with ANOVA calculations, response surface models are used in lieu of computationally intensive finite element solutions. From the sensitivity studies, parameter importance is assessed as a function of frequency. In addition, the work presents an approach to evaluate the probability that a parameter set exists to reconcile test with analysis. Comparisons of pre-test predictions of frequency response uncertainty bounds with measured data, results from the variancebased sensitivity analysis, and results from component test models with calibrated boundary stiffness models are all presented.

Ares I-X Launch Vehicle Modal Test Overview

The first test flight of NASA’s Ares I crew launch vehicle, called Ares I-X, is scheduled for launch in 2009. Ares I-X will use a 4-segment reusable solid rocket booster from the Space Shuttle heritage with mass simulators for the 5th segment, upper stage, crew module and launch abort system. Flight test data will provide important information on ascent loads, vehicle control, separation, and first stage reentry dynamics. As part of hardware verification, a series of modal tests were designed to verify the dynamic finite element model (FEM) used in loads assessments and flight control evaluations. Based on flight control system studies, the critical modes were the first three free-free bending mode pairs. Since a test of the free-free vehicle is not practical within project constraints, modal tests for several configurations in the nominal integration flow were defined to calibrate the FEM. A traceability study by Aerospace Corporation was used to identify the critical modes for the tested configurations. Test configurations included two partial stacks and the full Ares I-X launch vehicle on the Mobile Launcher Platform. This paper provides an overview for companion papers in the Ares I-X Modal Test Session. The requirements flow down, pre-test analysis, constraints and overall test planning are described.

Building structural acoustic response to aircraft sonic booms

As part of the NASA Low Boom/No Boom flight test project, a series of low‐amplitude sonic‐boom tests was completed over a 3‐week period in June of 2006. This series of flight tests was designed to evaluate indoor/outdoor human subjective response, structural acoustic building response, and the effects of atmospheric turbulence for low‐amplitude sonic booms characterized by overpressures in the nominal range of 0.1 to 0.6 pounds per square foot (psf). Low‐amplitude sonic booms were generated by F‐18 aircraft using dive trajectories to produce a range of overpressures at the Edwards Air Force Base housing area. In addition, straight and level supersonic flights were used to generate normal level (nominally 1.4 psf) sonic‐boom overpressures at the housing area. This report will describe the structural acoustic building response measurements obtained during this flight test project. A single‐family ranch‐style home was instrumented with nearly 300 microphone and accelerometer sensors to determine the incident...