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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 sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Smooth indentation of an initially stressed orthotropic beam

The contact behavior between a smooth rigid cylinder and a simply supported orthotropic beam under uniaxial initial stresses is studied. The displacements are computed by superposing Mindlin plate solution with the solution obtained from Biot's theory of incremental deformation. Finite Fourier transforms are used in solving the equations. A point matching technique is used to compute the contact stresses and the amount of indentation for a given contact length. The effects of orthotropy and initial stresses on the contact stress distribution are investigated. An indentation law is established from the numerical results.

Sun, C. T.↗
NASA NTRS1985

Application of two creep fatigue life models for the prediction of elevated temperature crack initiation of a nickel base alloy

Cyclic Damage Accumulation (CDA) and Total Strain-Strain Range Partitioning (TS-SRP) models for predicting the creep-fatigue crack initiation life of high temperature alloys are presented. The models differ in their fundamental assumptions regarding the controlling parameters for fatigue crack initiation and in the amount of data required to determine model constants. The CDA model represents a ductility exhaustion approach and uses stress quantities to calculate the cyclic fatigue damage. The TS-SRP model is based on the use of total mechanical strain and earlier concepts of the Strain Range Partitioning Method. Both models were applied to a well controlled fatigue data set at a high temperature nickel base alloy, B1900 + Hf, tested at 1600 F and 1800 F. The tests were divided into a baseline data set required to determine model constants and a verification data set for evaluation of the predictive capability of the models. Both models correlated the baseline data set to within factors of two in life, and predicted the verification data set to within a factor of three or better. In addition, sample calculations to demonstrate the application of each model and discusions of the predictive capabilities and areas requiring further development are presented.

Moreno, V.↗
NASA NTRS1986

Structure-to-property Relationships in Addition Cured Polymers 2: Resin Tg Composite Initial Mechanical Properties of Norbornenyl Cured Polyimide Resins

PRM (polymerization of monomeric reactants) methodology was used to prepare thirty different polyimide oligomeric resins. Monomeric composition as well as chain length between sites of crosslinks were varied to examine their effects on glass transition temperature (Tg) of the cured/postcured resins. An almost linear correlation of Tg versus molecular distance between the crosslinks was observed. An attempt was made to correlate Tg with initial mechanical properties (flexural strength and interlaminar shear strength) of unidirectional graphite fiber composites prepared with these resins. However, the scatter in mechanical strength data prevented obtaining as clear a correlation as was observed for the structural modification/crosslink distance versus Tg. Instead, only a range of composite mechanical properties was obtained at the test temperatures studied (room temperature, 288 and 316 C). Perhaps more importantly, what did become apparent during the attempted correlation study was: (1) that PMR methodology could be used to prepare composites from resins that contain a wide variety of monomer modifications, and (2) that these composites almost invariably provided satisfactory initial mechanical properties as long as the resins selected were melt processable.

Alston, W. B.↗
NASA NTRS1985

Young thrust-fault scarps in the highlands - Evidence for an initially totally molten moon

Attention is given to thermoelastic stress calculations implying that if only the outer few hundreds of km of a moon with a cool interior were initially molten, the lunar highlands should not have young compressional tectonic features. Extrapolations from Apollo panoramic images showing young thrust faults in the highlands suggest that about 2000 thrust fault scarps exist on the highlands, generally occurring in series or complexes of four or five scarps that are on average 5 km long. The ages of the scarps range from 60 + or - 30 to 680 + or - 250 my, with a possible factor bias of +2 to -4. The scarps are the youngest endogenic features on the moon, and indicate that the moon was initially molten.

Binder, A. B.↗
NASA NTRS1985

Low-velocity impact response of laminated beams subjected to initial stresses

Finite element procedures are used in conjunction with a numerical algorithm to compute the impact response of a graphite-epoxy laminated beam subjected to tensile initial stresses. The effect of initial stresses on the contact duration, impact force, coefficient of restitution, and bending and shear stresses are discussed. The analytically computed contact force history and strain response are compared with some experimental results.

Sankar, B. V.↗
NASA NTRS1985

On the impact of initially stressed composite laminates

The impact response behavior of initially stressed composite laminates is investigated using the finite element method. An experimentally established contact law is incorporated into the finite element program. The Newmark time integration algorithm is used for solving the time dependent equations of the plate and the impactor. Numerical results, including the contact force history, deflection, and strain in the plate, are presented. Effects of impact velocity, initial stress, and the mass and size of the impactor are discussed.

Sun, C. T.↗
NASA NTRS1986

Euler equation analysis of the initial roll-up of aircraft wakes

A new approach has been developed to study the initial roll-up of aircraft wakes. This approach is based on the solution of the three-dimensional Euler equations subject to inflow and initial conditions predicted by a vortex-lattice method. This procedure allows for the solution of this complex problem without any empirical inputs. However, valid solutions are limited to those flowfields generated by wings which are free of flow separation. Results are presented for four configurations: a rectangular wing with part span flap, a rectangular wing, a typical transport-type configuration and a fighter configuration. In addition, an assessment of an 'unsteady 2-D analogy' was undertaken using the 2-D time accurate Euler equation solutions in crossflow planes. In general, predictions from the 2-D unsteady analogy coincided with the 3-D results which were found to be in good agreement with available experimental data.

Mitcheltree, R. A.↗
NASA NTRS1986

Utilization of VAS satellite data in the initialization of an oceanic-cyclogenesis simulation

A series of experiments was performed to test various method of incorporating Visible Infrared Spin Scan Radiometer Atmospheric Sounder (VAS)-sounding data into the initial conditions of the Penn State University/National Center for Atmospheric mesoscale model. The VAS data for this ocean-cyclogenesis case consist of 110 irregularly distributed temperature and humidity soundings located over the North Pacific Ocean and apply at approximately 1200 GMT 10 November 1981. Various methods of utilizing VAS data in the initial condition of a mesoscale model were evaluated.

Douglas, Sharon G.↗
NASA NTRS1986

Highlights of contractor initiatives in quality enhancement and productivity improvement

The NASA/Contractor Team efforts are presented as part of NASA's continuing effort to facilitate the sharing of quality and productivity improvement ideas among its contractors. This complilation is not meant to be a comprehensive review of contractor initiative nor does it necessarily express NASA's views. The submissions represent samples from a general survey, and were not edited by NASA. The efforts are examples of quality and productivity programs in private industry, and as such, highlight company efforts in individual areas. Topics range from modernization of equipment, hardware, and technology to management of human resources. Of particular interest are contractor initiatives which deal with measurement and evaluation data pertaining to quality and productivity performance.

Source record↗
NASA NTRS1987

Initial utilization of the CVIRB video production facility

Video disk technology is one of the central themes of a technology demonstrator workstation being assembled as a man/machine interface for the Space Station Data Management Test Bed at Johnson Space Center. Langley Research Center personnel involved in the conception and implementation of this workstation have assembled a video production facility to allow production of video disk material for this propose. This paper documents the initial familiarization efforts in the field of video production for those personnel and that facility. Although the entire video disk production cycle was not operational for this initial effort, the production of a simulated disk on video tape did acquaint the personnel with the processes involved and with the operation of the hardware. Invaluable experience in storyboarding, script writing, audio and video recording, and audio and video editing was gained in the production process.

Parrish, Russell V.↗
NASA NTRS1986

The effect of a small initial curvature on the free vibration of clamped, rectangular plates

An analytical method of obtaining the natural frequencies and mode shapes of clamped, rectangular plates having a small initial curvature is presented. Specifically, the singular perturbation technique is used to reduce the fourth-order plate vibration problem to the simpler membrane problem with modified boundary conditions that account for the bending effects. The eigenfrequencies for plates with inverse aspect ratios varying between 0.1 and 1.0 and for the dimensionless normal prestress between 0.1 and 1.0 have been presented for values of epsilon, the normalized bending rigidity, ranging between 0.0010 and 0.2500. It is established that a small initial curvature has no effect on the frequency of vibration of the plate. However, its effect is manifested in the eigenmodes.

Adeniji-Fashola, A. A.↗
NASA NTRS1986

Initiation of breakdown in slender compressible vortices

The initiation of the breakdown process for axially symmetric compressible flows is investigated using a numerical solution of the conservation equations for mass, momentum, and energy. The vortex is isolated, with its axis parallel to the direction of the main stream, and the core radius is small compared to the breakdown length. Computations for several flowfields indicate that the breakdown of the solution is shifted further downstream with increasing Mach number until breakdown is no longer observed. In the subsonic case, the influence of the initial temperature distribution on the breakdown length of the solution is more pronounced than in the supersonic case, with heating of the core enhancing breakdown, and cooling delaying it. The breakdown of the solution is seen to always occur for nonvanishing axial velocity components.

Krause, E.↗
NASA NTRS1986

Structure-to-property relationships in addition cured polymers. II - Resin Tg and composite initial mechanical properties of norbornenyl cured polyimide resins

PRM (polymerization of monomeric reactants) methodology was used to prepare thirty different polyimide oligomeric resins. Monomeric composition as well as chain length between sites of crosslinks were varied to examine their effects on glass transition temperature (Tg) of the cured/postcured resins. An almost linear correlation of Tg versus molecular distance between the crosslinks was observed. An attempt was made to correlate Tg with initial mechanical properties (flexural strength and interlaminar shear strength) of unidirectional graphite fiber composites prepared with these resins. However, the scatter in mechanical strength data prevented obtaining as clear a correlation as was observed for the structural modification/crosslink distance versus Tg. Instead, only a range of composite mechanical properties was obtained at the test temperatures studied (room temperature, 288 and 316 C). Perhaps more importantly, what did become apparent during the attempted correlation study was: (1) that PMR methodology could be used to prepare composites from resins that contain a wide variety of monomer modifications, and (2) that these composites almost invariably provided satisfactory initial mechanical properties as long as the resins selected were melt processable.

Alston, William B.↗
NASA NTRS1987

Convenient stability criteria for difference approximations of hyperbolic initial-boundary value problems. II

The results of Goldberg and Tadmor (1985) are extended to achieve improved stability criteria for a large class of approximations to the initial boundary value problem associated with a particular hyperbolic system in a quarter plane. In a stability analysis, it is shown that the entire approximation is stable if and only if the scalar outflow components of its principal part are stable. Thus, the global stability question is reduced to that of a scalar, homogeneous outflow problem. The stability criteria for the reduced problem, which depend both on the basic scheme and the boundary conditions, but very little on the interaction between the two, are stated and used to establish previous examples and new ones, including a host of dissipative and nondissipative examples. There is no difficulty in extending the stability criteria to two-boundary problems and initial-boundary value problems with variable coefficients.

Goldberg, Moshe↗
NASA NTRS1986

Stability of semidiscrete approximations for hyperbolic initial-boundary-value problems: An eigenvalue analysis

A hyperbolic initial-boundary-value problem can be approximated by a system of ordinary differential equations (ODEs) by replacing the spatial derivatives by finite-difference approximations. The resulting system of ODEs is called a semidiscrete approximation. A complication is the fact that more boundary conditions are required for the spatially discrete approximation than are specified for the partial differential equation. Consequently, additional numerical boundary conditions are required and improper treatment of these additional conditions can lead to instability. For a linear initial-boundary-value problem (IBVP) with homogeneous analytical boundary conditions, the semidiscrete approximation results in a system of ODEs of the form du/dt = Au whose solution can be written as u(t) = exp(At)u(O). Lax-Richtmyer stability requires that the matrix norm of exp(At) be uniformly bounded for O less than or = t less than or = T independent of the spatial mesh size. Although the classical Lax-Richtmyer stability definition involves a conventional vector norm, there is no known algebraic test for the uniform boundedness of the matrix norm of exp(At) for hyperbolic IBVPs. An alternative but more complicated stability definition is used in the theory developed by Gustafsson, Kreiss, and Sundstrom (GKS). The two methods are compared.

Warming, Robert F.↗
NASA NTRS1987

Initial dynamic load estimates during configuration design

This analysis includes the structural response to shock and vibration and evaluates the maximum deflections and material stresses and the potential for the occurrence of elastic instability, fatigue and fracture. The required computations are often performed by means of finite element analysis (FEA) computer programs in which the structure is simulated by a finite element model which may contain thousands of elements. The formulation of a finite element model can be time consuming, and substantial additional modeling effort may be necessary if the structure requires significant changes after initial analysis. Rapid methods for obtaining rough estimates of the structural response to shock and vibration are presented for the purpose of providing guidance during the initial mechanical design configuration stage.

Schiff, Daniel↗
NASA NTRS1988

Correlations of norbornenyl crosslinked polyimide resin structures with resin thermo-oxidative stability, resin glass transition temperature and composite initial mechanical properties

PMR (polymerization of monomeric reactants) methodology was used to prepare 70 different polyimide oligomeric resins and 30 different unidirectional graphite fiber/polyimide composites. Monomeric composition as well as chain length between sites of crosslinks were varied to examine their effects on resin thermo-oxidative stability and glass transition temperature (Tg) of the cured/postcured resins. A linear correlation of decreasing 316 C resin weight loss/surface area versus (1) decreasing aliphatic content, or (2) increasing benzylic/aliphatic content stoichiometry ratio over a wide range of resin compositions was observed. An almost linear correlation of Tg versus molecular distance between the crosslinks was also observed. An attempt was made to correlate Tg with initial composite mechanical properties (flexural strength and interlaminar shear strength). However, the scatter in mechanical strength data prevented obtaining a clear correlation. Instead, only a range of composite mechanical properties was obtained at 25, 288, and 316 C. Perhaps more importantly, what did become apparent during the correlation study was (1) the PMR methodology could be used to prepare composites from resins containing a wide variety of monomer modifications, (2) that these composites almost invariably provided satisfactory initial mechanical properties as long as the resins formulated exhibited satisfactory processing flow, and (3) that PMR resins exhibited predictable rates of 316 C weight loss/surface area based on their benzylic/aliphatic stoichiometery ratio.

Alston, William B.↗
NASA NTRS1988

Development and verification of NASA Standard Initiator-2 (NSI-2)

The results of verification testing under NASA Contract NAS9-17249 are summarized in this Final Report. An Appendix is published separately. The report contains a brief discussion of design elements, test results, and a discussion of the latter. The contract was awarded for development and demonstration of design modifications to the NASA Standard Initiator-1 (NSI-1), resulting in the development of NSI-2. The intent of the project was to develop and prove the following design features: (1) Protection from premature initiation due to electrostatic potential by means other than a spark gap; (2) Development of an integral insulated charge cup for use with a zirconium/potassium perchlorate type mixture; (3) Improved cost and reliability figures by the use of a deposited ridge; and (4) Elimination of dudding as a result of the pyrotechnic shock effect, the movement of the primer composition away from the bridge circuit.

Corbin-Roberts, Linda↗