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At least 343 records · Page 19

All sources NASA NTRS DOE OSTI

NASA NTRS2013

Unit-Sphere Anisotropic Multiaxial Stochastic-Strength Model Probability Density Distribution for the Orientation of Critical Flaws

Models that predict the failure probability of monolithic glass and ceramic components under multiaxial loading have been developed by authors such as Batdorf, Evans, and Matsuo. These "unit-sphere" failure models assume that the strength-controlling flaws are randomly oriented, noninteracting planar microcracks of specified geometry but of variable size. This report develops a formulation to describe the probability density distribution of the orientation of critical strength-controlling flaws that results from an applied load. This distribution is a function of the multiaxial stress state, the shear sensitivity of the flaws, the Weibull modulus, and the strength anisotropy. Examples are provided showing the predicted response on the unit sphere for various stress states for isotropic and transversely isotropic (anisotropic) materials--including the most probable orientation of critical flaws for offset uniaxial loads with strength anisotropy. The author anticipates that this information could be used to determine anisotropic stiffness degradation or anisotropic damage evolution for individual brittle (or quasi-brittle) composite material constituents within finite element or micromechanics-based software

Nemeth, Noel↗

NASA NTRS2024

Effect of High-Speed Rotation on High-Temperature Superconducting Coils for High Efficiency Megawatt Motor

The use of a superconducting rotor in the High Efficiency Megawatt Motor (HEMM) comes with a number of challenges. The HEMM’s rotor must be designed so that the superconducting coil can tolerate the forces it will encounter during operation. These forces introduce considerable risk to the design of the HEMM. Because this risk cannot be adequately addressed through refined analysis, a set of experiments was deemed necessary to demonstrate that the HEMM’s superconducting coils can survive the stresses imparted by the centrifugal forces acting on the coil during full-speed operation of the machine. These experiments required spin testing a full-scale HEMM coil on a representative rotor structure at room temperature and sequentially higher rotation speeds and measuring the superconductivity response of the coil in liquid nitrogen (LN2) before and after each spin test. Tests were carried out to the full centripetal loading of a recent HEMM design. According to finite element analysis, this load produced stress components in the coil that exceed their design limit by a factor of 1 to 7.4. Although not yet confirmed, the current HEMM design is expected to produce even smaller stresses in the coil due to a 20 percent reduction in the coil’s mass and an increased volume of structural material. The only degradation of the coil that occurred during this testing resulted from a test rig failure and from the voltage taps, which are not part of the final coil design.

Electrified Aircraft Propulsion↗

NASA NTRS2026

Manufacturing and Scale-Up of Natural Fiber Composite eVTOL Propeller Skin and C-Channel

This report presents the manufacturing and scale-up of natural fiber composites for aerospace applications, conducted within NASA’s Convergent Aeronautics Solutions portfolio to advance aircraft capabilities and efficiency. The effort focused on the development and demonstration of two proof-of-concept articles, an Electric Vertical Take-off and Landing (eVTOL) propeller skin and a C-channel, produced through an iterative design and process optimization approach. Best practices and guidance on addressing key challenges with bio-based composite materials and manufacturing is provided. Ideally suited for non-load-bearing structural components, these emerging materials offer potential for weight reduction, vibration damping, noise mitigation, interference-free communication, and cost savings, without compromising the performance of safety-critical primary structures.

Natural fibers↗

DOE OSTI2020

Conceptual Design Study of a Thermal Energy Storage System Using Granular Solids for Coal-fired Boilers

<span style="font-size: 12pt;">Presentation for the 2020 International Pittsburgh Coal Conference held virtually from September 8-11, 2020.</span><span style="font-size: 12pt;">Abstract: As electricity from various renewable energy sources is increasingly supplied to the power grid, the grid’s stability will be challenged. Proposed grid-stability solutions will need to address variability of sources, such as solar and wind energy, in order to alleviate problems such as overgeneration and ramping. In regions where increases in solar energy are prominent, such as California, the net power demand curve often referred to as “the Duck Curve,” has caused problems for energy dispatchers, due to over-generation and fast ramping demands. In this project, we investigated a conceptual design for a Thermal Energy Storage System (TESS) integrated into a coal-fired power plant to support grid-scale storage. Implementing a TESS into power plants can allow for an increase in renewable sources, increase grid resilience, and allow conventional coal-fired plants to operate more efficiently. For this project, a TESS using granular solids as the energy-storage media is integrated into a conventional coal-fired power plant. The purpose of the TESS is to store energy from the flue gas during low demand periods and transfer the energy to steam during peak demand periods. The storage allows the stabilization of combustion and related boiler components at low loads and provides the opportunity to avoid some shutdowns. This study uses thermodynamic properties of several candidate thermal storage materials to estimate the size of storage system required for several operating scenarios. </span>

Huckaby, E. David↗

DOE OSTI2023

Influence on Structural Loading of a Wave Energy Converter by Controlling Variable-Geometry Components and the Power Take-Off

Oceans are harsh environments and can impose significant loads on deployed structures. A wave energy converter (WEC) should be designed to maximize the energy absorbed while ensuring the operating wave condition does not exceed the failure limits of the device itself. Therefore, the loads endured by the support structure are a design constraint for the system. Furthermore, the WEC should be adaptable to different sea states. Herethis work uses a WEC-Sim model of a variable-geometry oscillating wave energy converter (VGOSWEC) mounted on a support structure simulated under different wave scenarios. A VGOSWEC resembles a paddle pitching about a fixed hinge perpendicular to the incoming wave fronts. The geometry of the VGOSWEC is varied by opening a series of controllable flaps on the pitching paddle when the structure experiences threshold loads. It is hypothesized that opening the flaps should result in load shedding at the base of the support structure by reducing the moments about the hinge axis. This work compares the hydrodynamic coefficients, natural periods, and response amplitude operators from completely closed to completely open configurations of the controllable flaps. This work shows that the completely open configuration can reduce the pitch and surge loads on the base of the support structure by as much as 80%. Increased loads at the structure’s natural period can be mitigated by an axial power take-off damping acting as an additional design parameter to control the loads at the WEC’s support structure.

16 TIDAL AND WAVE POWER↗

DOE OSTI2022

Influence on Structural Loading of a Wave Energy Converter by Controlling Variable-Geometry Components and the Power Take-Off

Oceans are harsh environments and can impose significant loads on deployed structures. The deployment of wave energy converters (WECs) faces a design challenge with apparently contradictory goals. A WEC should be designed to maximize the energy absorbed while ensuring the operating wave condition does not exceed the failure limits of the device itself. Therefore, the loads endured by the support structure are a design constraint for the system. Adaptability to different sea states is, therefore, highly desirable. This work uses a WEC-Sim model of a variable-geometry oscillating wave energy converter (VGOSWEC) mounted on a support structure simulated under different wave scenarios. A VGOSWEC resembles a paddle pitching about a fixed hinge perpendicular to the incoming wave fronts. Therefore, the hinge experiences loads perpendicular to its axis as it maintains its position. The geometry of the VGOSWEC is varied by opening a series of controllable flaps on the pitching paddle when the structure experiences threshold loads. Because opening the flaps lets the waves transmit through the paddle, it is hypothesized that opening the flaps should result in load shedding at the base of the support structure. The load shedding is achieved by reducing the moments about the hinge axis. This work compares the hydrodynamic coefficients, natural periods, and response amplitude operators from completely closed to completely open configurations of the controllable flaps. The comparisons quantify the effects of letting the waves transmit through the VGOSWEC. This work shows that the completely open configuration can reduce the pitch and surge loads on the base of the support structure by as much as 80%. It was observed that at the paddle's resonance frequency, the loads on the structure increased substantially. This increase in loads can be mitigated by a rotational power take-off damping about the hinge axis. Changing the rotational power take-off damping was identified as an additional design parameter that can be used to control the loads experienced by the WEC's support structure.

fixed and floating structures↗

NASA NTRS1988

Truss-core corrugation for compressive loads

A corrugated panel structure for supporting compressive loads is described which includes curved cap strips separated by truss-core web segments. The truss-core web segments are formed from first and second flat panels with a corrugated filler in between them. The corrugated filler extends in the direction of the compressive load. As a result, all components of the panel structure have a compressive load carrying capability resulting in a high strength-to-weight ratio when the compressive load is limiting. Application to rocket and aircraft structures is suggested.

Randall C Davis↗

NASA NTRS2003

Evaluation of the Spherical Flange Concept for a Rocket Engine

Due to the inherent tolerance variability of hardware, flange misalignments occur during installation of mating components for a liquid propellant rocket engine. Flange misalignments include axial, lateral, and angular offsets. If these misalignments are high, they can impart significant loads into the two mating components. These significant loads can then be a driver in the design of the propellant ducts. Such was the case for the Rocketdyne RS-83 engine design for the Space Launch Initiative Program. To address this flange misalignment issue, Marshall Space Flight Center joined with Rocketdyne to develop and test a spherical flange system that allows for misalignment, yet reduces loads imparted, and at the same time provides sufficient sealing against leakage. The flange design was tested to evaluate and compare performance parameters such as misalignment and leakage. The environmental conditions ranged from -100 to 400 degrees Fahrenheit (F) with 1000 to 4000 pounds per square inch gage (psig) pressure. The desirable design features will be extracted and synthesized into a new flange design concept. This paper will address the spherical flange design and the test results.

Nichols, Jay↗

NASA NTRS1974

Converter design techniques and applications

Transistorized direct current voltage converters offer a number of advantages over other types because of their small size, low weight, high efficiency, high reliability, precision accuracy and wide range of control. There are three basic types of converter subsystems: series converter in which a voltage-controlled component is placed in series with the load; shunt converter in which a current-controlled component is placed in shunt with the load; and a switching converter in which a voltage-controlled component is turned on and off in series with the load. Converters employing any of these three types of subsystems can provide constant voltage, constant current, or constant impedance across the load. Design and application considerations, step-by-step design procedures, and the solution to sample design problems for the series, shunt, and switching types are presented.

Lalli, V. R.↗

NASA NTRS1986

The equivalent angle-of-attack concept for engineering analysis

An account is given of methods for the estimation of a wing-body-tail missile configuration's aerodynamic performance by means of the 'component buildup' method, in which the overall aerodynamic loads for an airframe are built up from the assumed characteristics of isolated airframe components and then subjected to additional loads generated by component interference. Attention is given to the cases of missile airframes in steady flow at arbitrary angles of attack and bank; the unifying thread of the present treatment is slender body theory, together with its nonlinear extensions through the equivalent angle-of-attack concept. The estimation of the forces and moments acting on each of the fins is emphasized, so that control cross-coupling effects as well as longitudinal and lateral directional effects can be determined.

Hemsch, M. J.↗

NASA NTRS1988

Elevated temperature crack growth

The problem of crack growth in hot path components such as combustor liners is complicated by several practical and theoretical considerations. The loading environment of such components involves high temperature levels and gradients that lead to considerations such as thermal stresses, crack closure, hold time, inelastic strains (both time dependent and independent), and Thermal Mechanical Fatigue (TMF). In general, a good understanding of the influence of these factors on crack growth was not obtained. At the same time, several nonlinear fracture mechanics parameters were suggested for such applications; however, most of the proposed methods were not tested for broad applications such as required for hot section components. It was the purpose of this program to evaluate proposed nonlinear methods by performing a thorough experimental and analytical study. The results illustrated that much progress was made in developing nonlinear methods.

Kim, K. S.↗

NASA NTRS1980

A flight investigation of performance and loads for a helicopter with 10-64C main rotor blade sections

A flight investigation produced data on performance and rotor loads for a teetering rotor, AH-1G helicopter flown with a main rotor that had the NLR-1T airfoil as the blade section contour. The test envelope included hover, forward flight speeds from 34 to 83 m/sec (65 to 162 knots), and collective fixed maneuvers at about 0.25 tip speed ratio. The data set for each test point describes vehicle flight state, control positions, rotor loads, power requirements, and blade motions. Rotor loads are reviewed primarily in terms of peak to peak and harmonic content. Lower frequency components predominated for most loads and generally increased with increased airspeed, but not necessarily with increased maneuver load factor. Detailed data for an advanced airfoil on an AH-1G are presented.

Morris, C. E. K.↗

NASA NTRS1991

A model for the progressive failure of laminated composite structural components

Laminated continuous fiber polymeric composites are capable of sustaining substantial load induced microstructural damage prior to component failure. Because this damage eventually leads to catastrophic failure, it is essential to capture the mechanics of progressive damage in any cogent life prediction model. For the past several years the authors have been developing one solution approach to this problem. In this approach the mechanics of matrix cracking and delamination are accounted for via locally averaged internal variables which account for the kinematics of microcracking. Damage progression is predicted by using phenomenologically based damage evolution laws which depend on the load history. The result is a nonlinear and path dependent constitutive model which has previously been implemented to a finite element computer code for analysis of structural components. Using an appropriate failure model, this algorithm can be used to predict component life. In this paper the model will be utilized to demonstrate the ability to predict the load path dependence of the damage and stresses in plates subjected to fatigue loading.

Allen, D. H.↗

NASA NTRSDate not supplied

Method Development for Experimental Characterization of Dynamic Strength of Aluminum Structures

Space Flight Hardware (SFH) experiences intense vibratory loading during flight, which only lasts a few minutes. When determining the appropriate size of these components to withstand such loading without becoming damaged, standard design practice is to assume that the peak dynamic loads are applied statically. In doing so, the resulting stress is compared against a material strength parameter obtained from a quasi-static experiment. Since the near-peak stresses are only experienced over a small fraction of time in reality, this approach leads to design conservatism that unnecessarily increases structural mass as well as the associated inefficiency and financial cost. In an effort to modernize engineering design standards to appropriately consider the higher practical strength of dynamically loaded structures, this overarching research project seeks to develop an experimental test procedure for quantifying the dynamic strength of metallic alloys as a function of excitation frequency. In the ideal case, the characterization test would include an in-situ method for monitoring the onset and progression of plastic deformation of the test specimen undergoing vibratory loading. These new tests are designed to be high intensity (forcing amplitude), short term (60 seconds at full amplitude), and cyclic in nature (sinusoidal excitation via attached stinger to an otherwise cantilevered beam). In addition, the initial alloy under investigation is 6061 aluminum, due to its wide use and applicability for SFH. Thus far, the primary candidate under development with live-capacity is to track hysteresis behavior of the beam from power dissipation trends, calculated via force (from transducer on excitation stinger) and velocity (measurements from Laser Doppler Vibrometer) data and work to distinguish between elastic and plastic features. As a key component of this ongoing method development, any pseudo-live indication of plasticity could be corroborated against the outcome of a pre-post assessment of damage via macroscopic evaluation of beam geometry (i.e. assessing any permanent change in the beam’s tip deflection). Support for experimental design decisions as well as dynamic strength data from tests with excitation frequencies of 10, 40, and 55 Hz will be discussed. This work contributes to the foundation for a new type of vibration-based characterization experiments and generates initial data on the functional strength of 6061 aluminum under the conditions considered.

vibrations, plastic deformation, aluminum, testing↗

NASA NTRSDate not supplied

Method Development for Experimental Characterization of Dynamic Strength of Aluminum Structures

Space Flight Hardware (SFH) experiences intense vibratory loading during flight, which only lasts a few minutes. When determining the appropriate size of these components to withstand such loading without becoming damaged (plastically deforming or breaking), standard design practice is to assume that the peak dynamic loads are applied statically. In doing so, the resulting stress is compared against a material strength parameter obtained from a quasi-static experiment. Since the near-peak stresses are only experienced over a small fraction of time in reality, this approach leads to design conservatism that unnecessarily increases structural mass as well as the associated inefficiency and financial cost. In an effort to modernize engineering design standards to appropriately consider the higher practical strength of dynamically loaded structures, this overarching research project seeks to develop an experimental test procedure for quantifying the dynamic strength of metallic alloys as a function of excitation frequency. In the ideal case, the characterization test would include an in-situ method for monitoring the onset and progression of plastic deformation of the test specimen undergoing vibratory loading. These new tests are designed to be high intensity (forcing amplitude), short term (60 seconds at full amplitude), and cyclic in nature (sinusoidal excitation via attached stinger to an otherwise cantilevered beam). In addition, the initial metallic alloy under investigation is 6061 aluminum, due to its wide use and applicability for SFH. Thus far, the most promising monitoring method under development with live-capacity is to track hysteresis behavior of the beam from power dissipation trends, calculated via force (from transducer on excitation stinger) and velocity (measurements from Laser Doppler Vibrometer) data and work to distinguish between elastic and plastic features. As a key component of this ongoing method development, any pseudo-live indication of plasticity can be corroborated against the outcome of a pre-post assessment of damage via macroscopic evaluation of beam geometry (i.e. assessing any permanent change in the beam’s tip deflection). Support for experimental design decisions as well as dynamic strength data from tests with excitation frequencies of 10, 40, and 55 Hz will be discussed. This work contributes to the foundation for a new type of vibration-based characterization experiments and generates initial data on the functional strength of 6061 aluminum under the conditions considered. Keywords: vibrations, plastic deformation, aluminum

vibrations↗

NASA NTRS1979

A flight investigation of performance and loads for a helicopter with NLR-1T main-rotor blade sections

Data on performance and rotor loads for a teetering-rotor, AH-1G helicopter flown with a main rotor that had the NLR-1T airfoil as the blade-section contour are presented. The test envelope included hover, forward-flight speed sweeps from 35 to 85 m/sec, and collective-fixed maneuvers at about 0.25 tip-speed ratio. The data set for each test point described vehicle flight state, control positions, rotor loads, power requirements, and blade motions. Rotor loads are reviewed primarily in terms of peak-to-peak and harmonic content. Lower frequency components predominated for most loads and generally increased with increased airspeed, but not necessarily with increased maneuver load factor.

Morris, C. E. K., Jr.↗

NASA NTRS1980

A flight investigation of performance and loads for a helicopter with RC-SC2 main-rotor blade sections

The test envelope included hover, forward-flight speed sweeps from 33 to 74 m/sec (65 to 144 knots), and collective-fixed maneuvers at about 0.25 tip-speed ratio. The data set for each test point describes vehicle flight states, control positions, rotor loads, power requirements and blade motions. Rotor loads were reviewed primarily in terms of peak-to-peak and harmonic content. Lower frequency components predominated for most loads and generally increased with increased airspeed, but not necessarily with increased maneuver load factor.

Morris, C. E. K., Jr.↗

NASA NTRS1985

Design procedures for fiber composite structural components: Panels subjected to combined in-plane loads

Step by step procedures are described which can be used to design panels made from fiber composite angleplied laminates and subjected to combined in plane loads. The procedures are set up as a multistep sample design. Steps in the sample design procedure range from selection of the laminate configuration to the subsequent analyses required to check design requirements for: (1) displacement, (2) ply stresses, and (3) buckling. The sample design steps are supplemented with appropriate tabular and graphical data which can be used to expedite the design process.

Chamis, C. C.↗