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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

The tensile and fatigue deformation structures in a single crystal Ni-base superalloy

Dislocation structures produced in Rene N4 crystals of various orientations deformed in tension and low cycle fatigue (LCF) at 760 and 980 degrees C were examined in order to elucidate the observed differences in stress-strain behavior. Specimens tensile tested at 760 degrees C displayed significant crystallographic orientation dependences in mechanical response but comparable inhomogeneous dislocation structures. LCF specimens of various orientations had comparable cyclic stress-strain curves and generally similar somewhat more homogeneous dislocation structures. Tensile specimens at the higher temperature had comparable mechanical response and corresponding similar quite homogeneous dislocation structures with gamma' faulting; and LCF specimens had orientation-dependent mechanical response but comparable homogeneous loose dislocation networks.

Gabb, T. P.↗
NASA NTRS1993

A Simplistic Look at Limit Stresses from Random Loading

Utilizing a continuous beam model, this report compares the potential stresses imposed on the beam from a random environment with those resulting from a typical static load analysis or test simulation. The Miles' equation used to develop peak response accelerations is shown to become a force equation in the hands of strength assessment personnel. This may prove to be unrealistic since hardware dynamic stresses are related to deflection rather than load. Correlation of the stress state for any static analysis or test with the actual dynamic response stress is strictly dependent upon how well the static deflections simulate the predominant dynamic mode shape. The report proposes that the general shape of this predominant mode, along with the peak response accelerations of major masses be used in strength assessments. From these data, a tailored enforced displacement loading may prove to be more effective in reproducing random induced stresses on flight hardware.

Lee, H. M.↗
NASA NTRS2018

Development and Application of a Tool for Optimizing Composite Matrix Viscoplastic Material Parameters

This document describes a recently developed analysis tool that enhances the resident capabilities of the Micromechanics Analysis Code with the Generalized Method of Cells (MAC/GMC) and its application. MAC/GMC is a composite material and laminate analysis software package developed at NASA Glenn Research Center. The primary focus of the current effort is to provide a graphical user interface (GUI) capability that helps users optimize highly nonlinear viscoplastic constitutive law parameters by fitting experimentally observed/measured stress-strain responses under various thermo-mechanical conditions for braided composites. The tool has been developed utilizing the MATrix LABoratory (MATLAB) (The Mathworks, Inc., Natick, MA) programming language. Illustrative examples shown are for a specific braided composite system wherein the matrix viscoplastic behavior is represented by a constitutive law described by seven parameters. The tool is general enough to fit any number of experimentally observed stress-strain responses of the material. The number of parameters to be optimized, as well as the importance given to each stress-strain response, are user choice. Three different optimization algorithms are included: (1) Optimization based on gradient method, (2) Genetic algorithm (GA) based optimization and (3) Particle Swarm Optimization (PSO). The user can mix and match the three algorithms. For example, one can start optimization with either 2 or 3 and then use the optimized solution to further fine tune with approach 1. The secondary focus of this paper is to demonstrate the application of this tool to optimize/calibrate parameters for a nonlinear viscoplastic matrix to predict stress-strain curves (for constituent and composite levels) at different rates, temperatures and/or loading conditions utilizing the Generalized Method of Cells. After preliminary validation of the tool through comparison with experimental results, a detailed virtual parametric study is presented wherein the combined effects of temperature and loading rate on the predicted response of a braided composite is investigated.

thermo-mechanical; MATLAB; GUI-Based Too↗
NASA NTRS1995

Finite element buckling and postbuckling solutions for multilayered composite panels

A study is made of the buckling and postbuckling responses of flat, unstiffened composite panels subjected to various combinations of mechanical and thermal loads. The analysis is based on a first-order shear deformation von Karman-type plate theory. A mixed formulation is used with the fundamental unknowns consisting of the strain components, stress resultants and the generalized displacements of the plate. The stability boundary, postbuckling response and the sensitivity coefficients are evaluated. The sensitivity coefficients measure the sensitivity of the buckling and postbuckling responses to variations in the different lamination and material parameters of the panel. Numerical results are presented for both solid panels and panels with central circular cutouts. The results show the effects of the variations in the fiber orientation angels, aspect ratio of the panel, and the hole diameter (for panels with cutouts) on the stability boundary, postbuckling response and sensitivity coefficients.

Noor, Ahmed K.↗
NASA NTRS1992

Catecholaminergic responses to stressful motion stimuli, scopolamine plus amphetamine, and dexamethasone

Peripheral levels of epinephrine (EPI) and neoepinephrine (NE) generally rise following stressful motion stimuli. Effective anti-motion sickness drugs, scopolamine plus, d-amphetamine (S/D) and dexamthasone (DEX) modulate release of EPI and NE. This modulation may be of etiological relevance. Methods: Severe nausea was induced by exposure to coriolis simulation using a rotating chair. Chronic administration of S/D (0.4 and 5 mg/da) DEX (3 mg/day) and placebo preceded coriolis simulation. EPI and NE were measured immediately before and after simulation. A double-blind crossover design was used. Results: Nausea-induced elevations of EPI (2.5 fold, p less than .01) and NE were not diminished upon repeated exposure and adaptation to the stressor. Subjects with more pronounced elevations of EPI following simulation displayed higher resistance to stressful motion (p less .05). Alteration of peripheral catechlomaine levels following drug suggested that motion sickness was not mediated by peripheral catechlolamine receptor simulation. EPI and NE levels were 2.8 and 3.6-fold higher (p less than .03 and .01) after nausea without DEX treatment. DEX loading halved pre-stress levels of EPI and NE (p less than .05). Conclusions: Marked differences were noted in individual responses to drug and systematic responses of EPI and NE. It is possible that the responses of EPI to motion sickness may predict resistance to stressful motion and represent a peripheral manifestation of some as yet unknown central event of etiologic relevance.

Kohl, R. L.↗
NASA NTRS1954

Application of several methods for determining transfer functions and frequency response of aircraft from flight data

In the process of analyzing the longitudinal frequency-response characteristics of aircraft, information on some of the methods of analysis has been obtained by the Langley Aeronautical Laboratory of the National Advisory Committee for Aeronautics. In the investigation of these methods, the practical applications and limitations were stressed. In general, the methods considered may be classed as: (1) analysis of sinusoidal response, (2) analysis of transient response as to harmonic content through determination of the Fourier integral by manual or machine methods, and (3) analysis of the transient through the use of least-squares solutions of the coefficients of an assumed equation for either the transient time response or frequency response (sometimes referred to as curve-fitting methods). (author)

Eggleston, John M↗
DOE OSTI2020

Fungal community structure and function shifts with atmospheric nitrogen deposition

Fungal decomposition of soil organic matter depends on soil nitrogen (N) availability. This ecosystem process is being jeopardized by changes in N inputs that have resulted from a tripling of atmospheric N deposition in the last century. Soil fungi are impacted by atmospheric N deposition due to higher N availability, as soils are acidified, or as micronutrients become increasingly limiting. Fungal communities that persist with chronic N deposition may be enriched with traits that enable them to tolerate environmental stress, which may trade-off with traits enabling organic matter decomposition. We hypothesized that fungal communities would respond to N deposition by shifting community composition and functional gene abundances toward those that tolerate stress but are weak decomposers. We sampled soils at seven eastern US hardwood forests where ambient N deposition varied from 3.2 to 12.6 kg N ha -1 year -1 , five of which also have experimental plots where atmospheric N deposition was simulated through fertilizer application treatments (25–50 kg N ha -1 year -1 ). Fungal community and functional responses to fertilizer varied across the ambient N deposition gradient. Fungal biomass and richness increased with simulated N deposition at sites with low ambient deposition and decreased at sites with high ambient deposition. Fungal functional genes involved in hydrolysis of organic matter increased with ambient N deposition while genes involved in oxidation of organic matter decreased. One of four genes involved in generalized abiotic stress tolerance increased with ambient N deposition. In summary, we found that the divergent response to simulated N deposition depended on ambient N deposition levels. Fungal biomass, richness, and oxidative enzyme potential were reduced by N deposition where ambient N deposition was high suggesting fungal communities were pushed beyond an environmental stress threshold. Fungal community structure and function responses to N enrichment depended on ambient N deposition at a regional scale.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Drought shrinks terrestrial upland resilience to climate change

Abstract Aim Drought has been shown to alter terrestrial ecosystem carbon (C) and nitrogen (N) dynamics, and thus feedback to future climate. However, drought‐induced changes in terrestrial upland C and N pools and the drought response of soil carbon dioxide (CO 2 ) and nitrous oxide (N 2 O) fluxes are yet to be quantified. Location Global upland ecosystems. Time period 2000–2018. Major taxa studied Terrestrial C and N fluxes. Methods A meta‐analysis was conducted that compiled 1,344 measurements from 128 manipulative studies worldwide to obtain a general picture of terrestrial C and N cycling responses to soil drought stress and identify the primary driving factors. Results We showed that drought significantly decreased plant C pools, with stronger negative responses of aboveground than belowground C components. Drought significantly decreased soil respiration ( R S ) and N 2 O fluxes by 19% and 29%, respectively. There were non‐significant changes in soil organic C and N pools in response to drought; in contrast to a considerable decrease in soil dissolved organic C (−22%), there was a robust increase in soil nitrate‐N (26%) following short‐term drought impact. By relating net ecosystem productivity (NEP) to the difference between net primary production (NPP) and soil heterotrophic respiration ( R H ), drought was found to drive a decrease up to −37% in NEP, being equivalent to a reduction in terrestrial net C uptake of 2.91 t C/ha. Main conclusions Our study provides insights into soil release of CO 2 and N 2 O with a linkage to the changes in terrestrial C and N pools in response to drought across upland biomes. Our findings highlight that, despite the lowered soil C release rate, the capacity of upland biomes as a C sink to slow climate change would still be weakened due to a robust decline of plant‐derived C input to soil in a future drier climate.

Zheng, Yajing↗
NASA NTRS1986

Immunological analyses of U.S. Space Shuttle crewmembers

Changes in the immunoresponsiveness of 'T' lymphocytes following space flight have been reported previously. Additional data collected before and after 11 Shuttle space flights show that absolute lymphocyte numbers, lymphocyte blastogenic capability, and eosinophil percent in the peripheral blood of crewmembers are generally depressed postflight. These responses resemble those associated with physical and emotional stress and may not be related to flight per se. Additional data from Space Shuttle flights 41B and 41D, involving 11 crewmembers, indicate a postflight decrease in cells reacting with 'B' lymphocyte and monocyte monoclonal antibody tags. Further, the loss of 'T' lymphocyte blast capability correlates with the decreased monocyte count (correlation coefficient = 0.697). This finding implies that the previously reported loss of blastogenic capability may be a function of decreased monocyte control, as noted in several nonspaceflight related studies.

Taylor, G. R.↗
NASA NTRS1987

Response of stiffened panels for applications to acoustic fatigue

The surface protection systems of aerospace and aircraft structures are often constructed from discretely stiffened panels. This paper presents an analytical study on dynamic stress response of these structures to random surface flow and acoustic loads. To account for aerodynamic heating of high speed flow, thermal effects are included in the structural model. A generalized transfer matrix procedure is developed to obtain the required dynamic response solutions. Numerical results include spectral densities of stress, response root mean square values and fatigue damage for a variety of loading and thermal conditions.

Vaicaitis, R.↗
NASA NTRSDate not supplied

Application of the MAT 213 Composite Impact Model to NASA Problems of Interest

A material model has been developed which incorporates several key capabilities which have been identified as lacking in currently available composite impact models. The material model utilizes experimentally based tabulated input to define the evolution of plasticity and damage as opposed to specifying discrete input parameters (such as modulus and strength). The material model has been implemented into LS-DYNA® as MAT 213. The model can simulate the nonlinear deformation, damage and failure that takes place in a composite under dynamic loading conditions. The deformation model utilizes an orthotropic plasticity formulation. For the damage model, the nonlinear unloading response that is observed prior to the point where the peak stress is reached can be simulated, as well as the stress degradation response that occurs after the peak stress is reached. A variety of failure models, including a generalized tabulated failure model which facilitates the utilization of general failure surfaces, have been implemented into MAT 213. Recent studies at NASA have concentrated on using MAT 213 to analyze both the impact and crush response of a variety of laminated and textile architectures. Several of these studies will be discussed in the presented paper. For example, a woven carbon/Kevlar composite is currently being examined for use in an energy absorber system for rotorcraft structures. MAT 213 analyses have been conducted to examine the ability of the model to accurately simulate the dynamic crush response of this material. Studies are also being conducted to examine the ability of MAT 213 to simulate the ballistic impact response of representative laminated and woven thermoplastic and thermoset matrix composites. NASA efforts are also concentrated on developing methods and processes for improving characterization methods and developing “best practices” for using MAT 213, a summary of which will be discussed in the paper.

Polymer Matrix Composites↗
NASA NTRS2008

Reliability Assessment of Graphite Specimens under Multiaxial Stresses

An investigation was conducted to predict the failure strength response of IG-100 nuclear grade graphite exposed to multiaxial stresses. As part of this effort, a review of failure criteria accounting for the stochastic strength response is provided. The experimental work was performed in the early 1990s at the Oak Ridge National Laboratory (ORNL) on hollow graphite tubes under the action of axial tensile loading and internal pressurization. As part of the investigation, finite-element analysis (FEA) was performed and compared with results of FEA from the original ORNL report. The new analysis generally compared well with the original analysis, although some discrepancies in the location of peak stresses was noted. The Ceramics Analysis and Reliability Evaluation of Structures Life prediction code (CARES/Life) was used with the FEA results to predict the quadrants I (tensile-tensile) and quadrant IV (compression-tension) strength response of the graphite tubes for the principle of independent action (PIA), the Weibull normal stress averaging (NSA), and the Batdorf multiaxial failure theories. The CARES/Life reliability analysis showed that all three failure theories gave similar results in quadrant I but that in quadrant IV, the PIA and Weibull normal stress-averaging theories were not conservative, whereas the Batdorf theory was able to correlate well with experimental results. The conclusion of the study was that the Batdorf theory should generally be used to predict the reliability response of graphite and brittle materials in multiaxial loading situations.

Sookdeo, Steven↗
NASA NTRS2003

High-Fidelity Micromechanics Model Enhanced for Multiphase Particulate Materials

This 3-year effort involves the development of a comprehensive micromechanics model and a related computer code, capable of accurately estimating both the average response and the local stress and strain fields in the individual phases, assuming both elastic and inelastic behavior. During the first year (fiscal year 2001) of the investigation, a version of the model called the High-Fidelity Generalized Method of Cells (HFGMC) was successfully completed for the thermo-inelastic response of continuously reinforced multiphased materials with arbitrary periodic microstructures (refs. 1 and 2). The model s excellent predictive capability for both the macroscopic response and the microlevel stress and strain fields was demonstrated through comparison with exact analytical and finite element solutions. This year, HFGMC was further extended in two technologically significant ways. The first enhancement entailed the incorporation of fiber/matrix debonding capability into the two-dimensional version of HFGMC for modeling the response of unidirectionally reinforced composites such as titanium matrix composites, which exhibit poor fiber/matrix bond. Comparison with experimental data validated the model s predictive capability. The second enhancement entailed further generalization of HFGMC to three dimensions to enable modeling the response of particulate-reinforced (discontinuous) composites in the elastic material behavior domain. Next year, the three-dimensional version will be generalized to encompass inelastic effects due to plasticity, viscoplasticity, and damage, as well as coupled electromagnetothermomechanical (including piezoelectric) effects.

Pindera, Marek-Jerzy↗
NASA NTRS1991

Deformation and stress response of composite laminated shells under internal pressure

This paper presents a theoretical study of the response of filament wound composite shells under internal pressure. Each layer of the material is generally cylindrically anisotropic. By using cylindrically anisotropic elasticity field equations and Lekhnitskii's stress functions, a system of sixth-order ordinary differential equations is obtained. The general expressions for the stresses and displacements in the laminated composite shells under internal pressure are discussed. Two composite systems, graphite/epoxy and glass/epoxy, are selected to demonstrate the influence of degree of material anisotropy and fiber orientations on the axial and induced twisting deformation. Stress distributions of (45/-45)s symmetric angle-ply fiber-reinforced laminated shells are shown to illustrate the effect of radius-to-thickness ratio.

Yuan, F. G.↗
NASA NTRS1991

HITCAN for actively cooled hot-composite thermostructural analysis

A computer code, high temperature composite analyzer (HITCAN), was developed to analyze/design hot metal matrix composite structures. HITCAN is a general purpose code for predicting the global structural and local stress-strain response of multilayered (arbitrarily oriented) metal matrix structures both at the constituent (fiber, matrix, and interphase) and the structural level, including the fabrication process effects. The thermomechanical properties of the constituents are considered to be nonlinearly dependent on several parameters, including temperature, stress, and stress rate. The computational procedure employs an incremental iterative nonlinear approach utilizing a multifactor-interaction material behavior model, i.e., the material properties are expressed in terms of a product of several factors that affect the properties. HITCAN structural analysis capabilities (static, load stepping - a multistep static analysis with material properties updated at each step, modal, and buckling) for cooled hot structures are demonstrated through a specific example problem.

Chamis, C. C.↗
NASA NTRS1992

HITCAN for actively cooled hot-composite thermostructural analysis

A computer code, high temperature composite analyzer (HITCAN), was developed to analyze/design hot metal matrix composite structures. HITCAN is a general purpose code for predicting the global structural and local stress-strain response of multilayered (arbitrarily oriented) metal matrix structures both at the constituent (fiber, matrix, and interphase) and the structural level, including the fabrication process effects. The thermomechanical properties of the constituents are considered to be nonlinearly dependent on several parameters, including temperature, stress, and stress rate. The computational procedure employs an incremental iterative nonlinear approach utilizing a multifactor-interaction material behavior model, i.e., the material properties are expressed in terms of a product of several factors that affect the properties. HITCAN structural analysis capabilities (static, load stepping - a multistep static analysis with material properties updated at each step, modal, and buckling) for cooled hot structures are demonstrated through a specific example problem.

Chamis, C. C.↗
NASA NTRS1990

HITCAN: High temperature composite analyzer

A computer code, HITCAN (High Temperature Composite Analyzer) was developed to analyze/design metal matrix composite structures. HITCAN is based on composite mechanics theories and computer codes developed at NASA LeRC over the last two decades. HITCAN is a general purpose code for predicting the global structural and local stress-strain response of multilayered (arbitrarily oriented) metal matrix structures both at the constituent (fiber, matrix, and interphase) and the structure level and including the fabrication process effects. The thermomechanical properties of the constituents are considered to be nonlinearly dependent on several parameters including temperature, stress, and stress rate. The computational procedure employs an incremental iterative nonlinear approach utilizing a multifactor-interaction material behavior model. HITCAN features and analysis capabilities (static, load stepping, modal, and buckling) are demonstrated through typical example problems.

Singhal, Surendra N.↗