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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 451 records · Page 25

All sources NASA NTRS DOE OSTI

NASA NTRS1987

Postbuckling and failure characteristics of stiffened graphite-epoxy shear webs

Results are presented from an experimental study of the postbuckling response and failure characteristics of flat, stiffened graphite-epoxy shear webs in which attention was given to the influence of stiffener attachment concepts, circular holes, and low speed impact damage on postbuckling performance. The laminate specimens chosen for testing are typical of those employed for transport aircraft primary structures. Test results show that low speed impact damage midway between stiffeners initiated specimen failure; the strength of an impact-damaged specimen was less than that of the corresponding control specimen.

Rouse, Marshall↗

NASA NTRS1991

Test chips and ASIC qualification

A test chip set being developed to aid in the qualification of spaceborne Application Specific Integrated Circuits (ASICs) is described. The chip set consists of a process monitor for process parameter verification, a fault chip for yield analysis, a reliability chip for ASIC failure rate analysis, and total ionizing dose and single event upset chips for radiation effect analysis. The test structures contained in these chips are discussed along with representative test results.

Buehler, M. G.↗

NASA NTRS1992

Middeck zero-gravity dynamics experiment - Comparison of ground and flight test data

An analytic and experimental study of the changes in the modal parameters of space structural test articles from one- to zero-gravity is presented. Deployable, erectable, and rotary modules was assembled to form three one- and two-dimensional structures, in which variations in bracing wire and rotary joint preload could be introduced. The structures were modeled as if hanging from a suspension system in one gravity, and unconstrained, as if free floating in zero-gravity. The analysis is compared with ground experimental measurements, made on a spring/wire suspension system with a nominal plunge frequency of one Hertz, and with measurements made on the Shuttle middeck. The degree of change in linear modal parameters as well as the change in nonlinear nature of the response is examined. Trends in modal parameters are presented as a function of force amplitude, joint preload, and ambient gravity level.

Crawley, Edward F.↗

NASA NTRS2020

Passive Aeroelastic Tailored Wing Modal Test Using the Fixed Base Correction Method

In modal testing and finite element model correlation, analysts desire modal results using free-free or rigid boundary conditions to ease comparisons of test versus analytical data. It is often expensive both in cost and schedule to build and test with boundary conditions that replicate the free-free or rigid boundaries. Static test fixtures for load testing are often large, heavy, and unyielding, but do not provide adequate boundaries for modal tests because they are dynamically too flexible and often contain natural frequencies within the frequency range of interest of the test article. Dynamic coupling between the test article and test fixture complicates the model updating process because significant effort is required to model the test fixture and boundary conditions in addition to the test article. If there were a way to correct the modal results for fixture coupling, then setups used for other structural testing could be adequate for modal testing. In the case described in this paper, a partial static loads testing setup was used, which allowed significant schedule and cost savings by eliminating a unique setup for a modal test. A fixed base correction technique was investigated during modal testing of a flexible wing cantilevered from part of a static test fixture. The technique was successfully used to measure the wing modes de-coupled from the dynamically active test fixture. The technique is promising for future aircraft applications, but more research is needed.

structural dynamics↗

NASA NTRS1987

Space station structures and dynamics test program

The design, construction, and operation of a low-Earth orbit space station poses unique challenges for development and implementation of new technology. The technology arises from the special requirement that the station be built and constructed to function in a weightless environment, where static loads are minimal and secondary to system dynamics and control problems. One specific challenge confronting NASA is the development of a dynamics test program for: (1) defining space station design requirements, and (2) identifying the characterizing phenomena affecting the station's design and development. A general definition of the space station dynamic test program, as proposed by MSFC, forms the subject of this report. The test proposal is a comprehensive structural dynamics program to be launched in support of the space station. The test program will help to define the key issues and/or problems inherent to large space structure analysis, design, and testing. Development of a parametric data base and verification of the math models and analytical analysis tools necessary for engineering support of the station's design, construction, and operation provide the impetus for the dynamics test program. The philosophy is to integrate dynamics into the design phase through extensive ground testing and analytical ground simulations of generic systems, prototype elements, and subassemblies. On-orbit testing of the station will also be used to define its capability.

Moore, Carleton J.↗

NASA NTRS1989

X-29A aircraft structural loads flight testing

The X-29A research and technology demonstrator aircraft has completed a highly successful multiphase flight test program. The primary research objective was to safely explore, evaluate, and validate a number of aerodynamic, structural, and flight control technologies, all highly integrated into the vehicle design. Most of these advanced technologies, particularly the forward-swept-wing platform, had a major impact on the structural design. Throughout the flight test program, structural loads clearance was an ongoing activity to provide a safe maneuvering envelope sufficient to accomplish the research objectives. An overview is presented of the technologies, flight test approach, key results, and lessons learned from the structural flight loads perspective. The overall design methodology was considered validated, but a number of structural load characteristics were either not adequately predicted or totally unanticipated prior to flight test. While conventional flight testing techniques were adequate to insure flight safety, advanced analysis tools played a key role in understanding some of the structural load characteristics, and in maximizing flight test productivity.

Sims, Robert↗

NASA NTRS1978

Analytical testing techniques

Structural dynamic analytical testing techniques can be a tool to determine the source of structural dynamic problems and the solution to these problems. Analytical testing techniques are based upon dynamic testing methods and analysis of test results. These methods apply primarily to constructed wind turbine systems. A summary of these methods is presented.

Jones, R.↗

NASA NTRS1991

Aging aircraft NDI Development and Demonstration Center (AANC): An overview

A major center with emphasis on validation of nondestructive inspection (NDI) techniques for aging aircraft, the Aging Aircraft NDI Development and Demonstration Center (AANC), has been funded by the FAA at Sandia National Laboratories. The Center has been assigned specific tasks in developing techniques for the nondestructive inspection of static engine parts, assessing inspection reliability (POD experiments), developing testbeds for NDI validation, maintaining a FAA library of characterized aircraft structural test specimens, and leasing a hangar to house a high flight cycle transport aircraft for use as a full scale test bed.

Aging Aircraft↗

DOE OSTI2021

Observations of modal coupling due to bolted joints in an experimental benchmark structure

The goal of this paper is to present a set of measurements from a benchmark structure containing two bolted joints to support future efforts to predict the damping due to the joints and to model nonlinear coupling between the first two elastic modes. Bolted joints introduce nonlinearities in structures, typically causing a softening in the natural frequency and an increase in damping because of frictional slip between the contact interfaces within the joint. These nonlinearities pose significant challenges when characterizing the response of the structure under a large range of load amplitudes, especially when the modal responses become coupled, causing the effective damping and natural frequency to not only depend on the excitation amplitude of the targeted mode, but also the relative amplitudes of other modes. In this work, two nominally identical benchmark structures, known in some prior works as the S4 beam, are tested to characterize their nonlinear properties for the first two elastic modes. Detailed surface measurements are presented and validated through finite element analysis and reveal distinct contact interactions between the two sets of beams. The free-free test structures are excited with an impact hammer and the transient response is analyzed to extract the damping and frequency backbone curves. A range of impact amplitudes and drive points are used to isolate a single mode or to excite both modes simultaneously. Differences in the nonlinear response correlate with the relative strength of the modes that are excited, allowing one to characterize mode coupling. Each of the beams shows different nonlinear properties for each mode, which is attributed to the different contact pressure distributions between the parts, although the mode coupling relationship is found to be consistent between the two. Lastly, the test data key finding are presented in this paper and the supporting data is available on a public repository for interested researchers.

42 ENGINEERING↗

NASA NTRS1986

Buckling characteristics of hypersonic aircraft wing tubular panels

The buckling characteristics of Rene 41 tubular panels installed as wing panels on a hypersonic wing test structure (HWTS) were determined nondestructively through use of a force/stiffness technique. The nondestructive buckling tests were carried out under different combined load conditions and different temperature environments. Two panels were subsequently tested to buckling failure in a universal tension compression testing machine. In spite of some data scattering because of large extrapolations of data points resulting from termination of the test at a somewhat low applied load, the overall test data correlated fairly well with theoretically predicted buckling interaction curves. The structural efficiency of the tubular panels was slightly higher than that of the beaded panels which they replaced.

Ko, William L.↗

NASA NTRS1985

On thermomechanical testing in support of constitutive equation development for high temperature alloys

Three major categories of testing are identified that are necessary to provide support for the development of constitutive equations for high temperature alloys. These are exploratory, charactrization and verification tests. Each category is addressed and specific examples of each are given. An extensive, but not exhaustive, set of references is provided concerning pertinent experimental results and their relationships to theoretical development. This guide to formulating a meaningful testing effort in support of consitutive equation development can also aid in defining the necessary testing equipment and instrumentation for the establishment of a deformation and structures testing laboratory.

Robinson, D. N.↗

NASA NTRS1991

Conducting the NASP ground test program

The National Aero-Space Plane (NASP) program has recently entered a new phase of the program known as Phase 2D. During this period, five aerospace companies and the Government have formed a National Team. This team has focused on developing a single experimental (X-30) vehicle design and are pursuing a technology validation and demonstration program to prove out the design concepts and design tools. This paper presents an overview of the Phase 2D round testing being conducted to validate the X-30 design and to demonstrate the critical technologies needed to build and fly a research vehicle during Phase 3 of the program. The Phase 2D exit criteria are discussed to identify how they provide top-level guidance for developing the ground test program. An overview of major test facility modifications being performed in support of the test program is also presented. Emphasis is placed on propulsion and structures testing since these are felt to be the primary areas requiring technologies beyond the current state-of-the-art. Also discussed is the use of uncertainty analysis as a method to account for uncertainties in test data. In addition, this paper addresses the use of these uncertainties to develop qualitative indicators of how well the design and technology developed during Phase 2 have matured.

Airframes↗

NASA NTRS1979

The development of the DAST I remotely piloted research vehicle for flight testing an active flutter suppression control system

The development of the DAST I (drones for aerodynamic and structural testing) remotely piloted research vehicle is described. The DAST I is a highly modified BQM-34E/F Firebee II Supersonic Aerial Target incorporating a swept supercritical wing designed to flutter within the vehicle's flight envelope. The predicted flutter and rigid body characteristics are presented. A description of the analysis and design of an active flutter suppression control system (FSS) designed to increase the flutter boundary of the DAST wing (ARW-1) by a factor of 20% is given. The design and development of the digital remotely augmented primary flight control system and on-board analog backup control system is presented. An evaluation of the near real-time flight flutter testing methods is made by comparing results of five flutter testing techniques on simulated DAST I flutter data. The development of the DAST ARW-1 state variable model used to generate time histories of simulated accelerometer responses is presented. This model uses control surface commands and a Dryden model gust as inputs. The feasibility of the concept of extracting open loop flutter characteristics from closed loop FSS responses was examined. It was shown that open loop characteristics can be determined very well from closed loop subcritical responses.

Grose, D. L.↗

NASA NTRS1972

Design, analysis, and tests of a structural prototype Viking aeroshell. I - Aeroshell design and analysis. II - Test procedure and test results.

Two near optimum full-scale Viking aeroshell prototypes (140 deg ring-stiffened conical shells), differing only in base ring size, were designed and tested under uniform pressure to buckling failure. Part I describes the computerized design procedure which iterates between a design program based on approximate equations to determine skin and ring gages and ring spacings, and a sophisticated system of shell of revolution programs for more accurate analysis as a basis for redesign. Part II discusses fabrication techniques, test procedures, and test results. Both buckling and prebuckling data are compared with the theoretical predictions of Part I. Appropriate buckling knockdown factors for this type of construction are identified. Measured strains in skin and rings agreed well with theoretical predictions and the buckling pressure was in close agreement with the design ultimate pressure.

Heard, W. L., Jr.↗

NASA NTRS1975

Criteria for analysis-test correlation of structural dynamic systems

A rational criterion for structural dynamic analysis-test correlation has been established by using a matrix perturbation technique. This criterion can be used for the verification of an analytical model by the test results. Also, the same technique can be applied to update the analytical results by using the test results without repeating the entire analytical procedure. A sample problem has been used to demonstrate this technique. Very satisfactory results are obtained with only the first-order perturbation solution included for transient loading. For periodic loading, higher-order perturbation solutions are needed to achieve the same accuracy.

Chen, J. C.↗

NASA NTRS1995

A 20k Payload Launch Vehicle Fast Track Development Concept Using an RD-180 Engine and a Centaur Upper Stage

A launch vehicle concept to deliver 20,000 lb of payload to a 100-nmi orbit has been defined. A new liquid oxygen/kerosene booster powered by an RD-180 engine was designed while using a slightly modified Centaur upper stage. The design, development, and test program met the imposed 40-mo schedule by elimination of major structural testing by increased factors of safety and concurrent engineering concepts. A growth path to attain 65,000 lb of payload is developed.

Toelle, Ronald↗

NASA NTRS2000

Propellant Densification Ground Testing Conducted for Launch Vehicles

The NASA Glenn Research Center at Lewis Field has taken the lead in the development of practical densified cryogenic propellants for launch vehicle applications. The technology of subcooling cryogenic propellants below their normal boiling point to produce a denser fluid is one of the key process technologies necessary to meet the challenge of single-stage-to-orbit and reusable launch vehicles. Densified propellants are critical to lowering launch costs because they enable more propellant to be packed into a given unit volume, thus improving the performance by reducing the overall size and weight of the launch vehicle. This two-pronged research and test program has evolved into (1) conducting tank loading tests using densified liquid hydrogen and (2) developing two large-scale propellant densification systems that will be performance tested next year at Glenn. The propellant-loading test program was undertaken at Glenn in coordination with Lockheed Martin Michoud Space Systems. In this testing, the liquid hydrogen recirculation and densification process was simulated, and the thermal stratification of the densified propellant was recorded throughout the tank. The test article was a flight-weight tank constructed from composite materials similar to those to be used on the X-33 launch vehicle. The tank geometry as designed by Lockheed Martin had two cylindrical lobes with a center septum. Liquid hydrogen flow rate, pressure data, and temperature data plotted over time were collected while the subscale tank was filled with 27 R (15 K) densified liquid hydrogen propellant. This testing has validated mathematical models and demonstrated the readiness of densified propellant technology for near-term use. It marks the first time that such a process has been carried out with a multiple-lobe, flight-similar tank. Glenn researchers have also been working on providing a process and critical test data for the continuous production of densified liquid hydrogen (LH2) and densified liquid oxygen (LO2). Each densification production process uses a high-efficiency, subatmospheric boiling bath heat exchanger to cool the working fluid. A near triple-point hydrogen boiling bath is used to condition and subcool hydrogen to 27 R (15 K), and a nitrogen boiling bath is used to cool the liquid oxygen to 120 R (66.7 K). Multistage centrifugal compressors operating at cryogenic inlet conditions maintain the heat exchanger bath vapor pressure below 1 atm. The LO2 propellant densification unit shown in the photograph has a 30 lb/sec capacity, whereas the LH2 unit was designed to process 8 lb/sec of propellant. Each densification unit will be transported to Glenn's South Forty area after all fabrication work is completed sometime late next year. There the LO2 and LH2 densifier performance tests will be conducted with another larger Lockheed Martin tank designated the Structural Test Article (STA). This liquid oxygen tank is a full-scale, flight-weight, prototype aluminum tank designed for the X-33. It has a capacity of 20,000 gallons of LO2. The tank loading and recirculation testing planned for next year with STA will provide the data necessary for full-scale development of propellant densification technology.

Tomsik, Thomas M.↗

NASA NTRS1972

Application of Rochrome liquid crystal tapes for thermographic testing of bonded structures

The use of ROCHROME liquid crystal tape for thermographic testing of bonded structures for aircraft is described. The techniques for applying the tape, heating the test panels, and photographing the resulting thermal patterns are described and discussed. The results obtained are compared with those reported previously for the same test panels coated directly with liquid crystals applied by spraying. Other panels previously examined by various nondestructive techniques, both by thermography, were also tested. Results for these latter panels are presented and discussed. For both sets of panels good correlation with previous work was obtained. Deficiencies associated with present ROCHROME tape are described. In general, these stem from the lack of optimization for materials testing of the ROCHROME tape, particularly with respect to the adhesive system and supporting film.

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