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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Analysis of the progressive failure of brittle matrix composites

This report investigates two of the most common modes of localized failures, namely, periodic fiber-bridged matrix cracks and transverse matrix cracks. A modification of Daniels' bundle theory is combined with Weibull's weakest link theory to model the statistical distribution of the periodic matrix cracking strength for an individual layer. Results of the model predictions are compared with experimental data from the open literature. Extensions to the model are made to account for possible imperfections within the layer (i.e., nonuniform fiber lengths, irregular crack spacing, and degraded in-situ fiber properties), and the results of these studies are presented. A generalized shear-lag analysis is derived which is capable of modeling the development of transverse matrix cracks in material systems having a general multilayer configuration and under states of full in-plane load. A method for computing the effective elastic properties for the damaged layer at the global level is detailed based upon the solution for the effects of the damage at the local level. This methodology is general in nature and is therefore also applicable to (0(sub m)/90(sub n))(sub s) systems. The characteristic stress-strain response for more general cases is shown to be qualitatively correct (experimental data is not available for a quantitative evaluation), and the damage evolution is recorded in terms of the matrix crack density as a function of the applied strain. Probabilistic effects are introduced to account for the statistical nature of the material strengths, thus allowing cumulative distribution curves for the probability of failure to be generated for each of the example laminates. Additionally, Oh and Finney's classic work on fracture location in brittle materials is extended and combined with the shear-lag analysis. The result is an analytical form for predicting the probability density function for the location of the next transverse crack occurrence within a crack bounded region. The results of this study verified qualitatively the validity of assuming a uniform crack spacing (as was done in the shear-lag model).

Thomas, David J.↗
NASA NTRS1994

Peripheral Microvascular Responses to Whole-Body Tilting, G(z) Centrifugation, and Lower Body Negative Pressure Stresses in Humans

The response of the cutaneous microcirculation to orthostatic stress varies along the length of the body due to the interaction of central controls with regional responses to local blood pressure. We hypothesize that artificial orthostatic stresses such as Gz centrifugation and LBNP differ from whole-body tilting in terms of the distribution of microvascular blood flow. Cutaneous microvascular flows were measured by laser Doppler flowmetry at the neck, thigh, and leg of 15 normal subjects. Volunteers underwent stepwise head-up tilt (HUT) and short- and long-arm centrifugation protocols from supine control (0 Gz) to 0.2, 0.4, 0.6, 0.8, 1.0, 0.8, 0.6, 0.4, 0.2, and 0 Gz at the feet, for 30-s periods with 10-s transitions between levels. The same subjects underwent a corresponding supine LBNP protocol, up to 100 mmHg (in 20 mmHg increments) and back to zero pressure, which produced transmural pressure across blood vessels in the foot approximately equal to the HUT protocol. In general, application of all orthostatic stresses produced significant flow reductions in the lower body (p less than 0.05) and inconsistent changes in the neck. At low levels of each stress (0.4 Gz, 40 mmHg), LBNP generated the greatest relative reduction in flow in the lower body (-66.9+/-5.7%, thigh; -60.6 +/-5.7%, leg, mean +/- SE). HUT caused a less severe flow reduction than LBNP at the thigh and leg (-39.9 +/- 8.1% and -55.9+/-4.8%), while the effects induced by both forms of centrifugation were the least profound. Higher levels of each stress generally resulted in similar responses. These responses exhibit a consistent relationship to hypothesized changes in local microvascular transmural pressure, suggesting that myogenic and veno-arteriolar reflexes play a significant role in determining microvascular perfusion during orthostatic stress.

Breit, G. A.↗
NASA NTRS1985

A comparison of smooth specimen and analytical simulation techniques for notched members at elevated temperatures

Experimental strain measurements have been made at the highly strained regions on notched plate specimens that were made of Hastelloy X. Tests were performed at temperatures up to 1,600 F. Variable load patterns were chosen so as to produce plastic and creep strains. Were appropriate, notch root stresses were experimentally estimated by subjecting a smooth specimen to the measured notch root strains. The results of three analysis techniques are presented and compared to the experimental data. The most accurate results were obtained from an analysis procedure that used a smooth specimen and the Neuber relation to simulate the notch root stress-strain response. When a generalized constitutive relation was used with the Neuber relation, good results were also obtained, however, these results were not as accurate as those obtained when the smooth specimen was used directly. Finally, a general finite element program, ANYSIS, was used which resulted in acceptable solutions, but, these were the least accurate predictions.

Martin, J. F.↗
NASA NTRS2014

Mechanisms of Orthostatic Tolerance Improvement Following Artificial Gravity Exposure Differ Between Men and Women

We recently determined that a short exposure to artificial gravity (AG) improved the orthostatic tolerance limit (OTL) of cardiovascularly deconditioned subjects. We now seek to determine the mechanisms of that improvement in these hypovolemic men and women. Methods. We determined the orthostatic tolerance limit (OTL) of 9 men and 8 women following a 90 min exposure to AG compared to 90 min of head down bed rest (HDBR). In both cases (21 days apart), subjects were made hypovolemic (low salt diet plus 20 mg intravenous furosemide). Orthostatic tolerance was determined from a combination of head up tilt and increasing lower body negative pressure until presyncope. Mean values and correlations with OTL were determined for heart rate, blood pressure, stroke volume, cardiac output and peripheral resistance (Finometer), cerebral artery blood velocity (DWL), partial pressure of carbon dioxide (Novametrics) and body segmental impedance (UFI THRIM) were measured during supine baseline, during OTL to presyncope and during supine recovery Results. Orthostatic tolerance of these hypovolemic subjects was significantly greater on the day of AG exposure than on the HDBR day. Regression of OTL on these variables identified significant relationships on the HDBR day that were not evident on the AG day: resting TPR correlated positively while resting cerebral flow correlated negatively with OTL. On both days, women's resting stroke volume correlated positively with orthostatic tolerance. Higher group mean values of stroke volume and cerebral artery flow and lower values of blood pressure, peripheral vascular and cerebrovascular resistance both at control and during OTL testing were observed on the AG day. Even though regression of OTL on resting stroke volume was significant only in women, presyncopal stroke volume reached the same level on each day of study for both men and women while the OTL test lasted 30% longer in men and 22% longer in women. Cerebral artery flow appeared to follow stroke volume and absolute values of cerebral flow did not correlate with the development of presyncope. Women responded to AG exposure with elevated cerebral flow at resting control and throughout the OTL test, implying a loss of autoregulation in deconditioned (hypovolemic) women following AG exposure. Conclusions. Before countermeasures to space flight cardiovascular deconditioning are established, gender differences in cardiovascular responses to orthostatic stress, in general, and to orthostatic stress following exposure to artificial gravity, in particular, need to be determined. Since, in both men and women, a single, acute bout of AG exposure improved orthostatic tolerance, the feasibility of short exposures to AG during longer spaceflights or prior to entry into a gravity (Earth or Mars) environment, should be explored. Given the known beneficial effects of AG on other organ systems, the present study indicates that the positive effects of AG on cardiac stroke volume make AG a likely candidate for maintaining cardiovascular conditioning.

Evans, J. M.↗
DOE OSTI2024

Cacao pod transcriptome profiling of seven genotypes identifies features associated with post-penetration resistance to Phytophthora palmivora

Abstract The oomycete Phytophthora palmivora infects the fruit of cacao trees ( Theobroma cacao ) causing black pod rot and reducing yields. Cacao genotypes vary in their resistance levels to P. palmivora , yet our understanding of how cacao fruit respond to the pathogen at the molecular level during disease establishment is limited. To address this issue, disease development and RNA-Seq studies were conducted on pods of seven cacao genotypes (ICS1, WFT, Gu133, Spa9, CCN51, Sca6 and Pound7) to better understand their reactions to the post-penetration stage of P. palmivora infection. The pod tissue- P. palmivora pathogen assay resulted in the genotypes being classified as susceptible (ICS1, WFT, Gu133 and Spa9) or resistant (CCN51, Sca6 and Pound7). The number of differentially expressed genes (DEGs) ranged from 1625 to 6957 depending on genotype. A custom gene correlation approach identified 34 correlation groups. De novo motif analysis was conducted on upstream promoter sequences of differentially expressed genes, identifying 76 novel motifs, 31 of which were over-represented in the upstream sequences of correlation groups and associated with gene ontology terms related to oxidative stress response, defense against fungal pathogens, general metabolism and cell function. Genes in one correlation group (Group 6) were strongly induced in all genotypes and enriched in genes annotated with defense-responsive terms. Expression pattern profiling revealed that genes in Group 6 were induced to higher levels in the resistant genotypes. An additional analysis allowed the identification of 17 candidate cis -regulatory modules likely to be involved in cacao defense against P. palmivora . This study is a comprehensive exploration of the cacao pod transcriptional response to P. palmivora spread after infection. We identified cacao genes, promoter motifs, and promoter motif combinations associated with post-penetration resistance to P. palmivora in cacao pods and provide this information as a resource to support future and ongoing efforts to breed P. palmivora -resistant cacao.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1983

Some Recent Developments in the Endochronic Theory with Application to Cyclic Histories

Constitutive equations with only two easily determined material constants predict the stress (strain) response of normalized mild steel to a variety of general strain (stress) histories, without a need for special unloading-reloading rules. The equations are derived from the endochronic theory of plasticity of isotropic materials with an intrinsic time scale defined in the plastic strain space. Agreement between theoretical predictions and experiments are are excellent quantitatively in cases of various uniaxial constant amplitude histories, variable uniaxial strain amplitude histories and cyclic relaxation. The cyclic ratcheting phenomenon is predicted by the present theory.

Valanis, K. C.↗
DOE OSTI2025

EcoBOT: an AI/ML enabled automated phenotyping capability for model plants

Introduction: Advances in automation and AI/ML offer new opportunities for plant science, including design, modeling, and analysis. This study aimed to develop an automated platform for researching small model plants under axenic conditions and integrate it with AI/ML tools. Methods: The EcoBOT platform was developed, which consists of sterile containers (EcoFABs) for growing plants and imaging for monitoring plant growth and health. Brachypodium distachyon was grown on the EcoBOT, and its response to nutrient limitation and copper stress was evaluated. Results: The results showed that Brachypodium distachyon grown in the EcoBOT maintained sterility and responded to nutrient limitation and copper stress. Analysis of over 6,500 root and shoot images revealed varying sensitivity and response rates to copper. Bayesian Optimization was used to improve model accuracies relating copper concentrations to plant biomass via sequential experiments, resulting in a >30% improvement. Discussion: The findings of this study demonstrate the potential of the EcoBOT platform for researching plant responses to environmental factors. Future experiments could focus on relating other chemical stresses and microbial interactions to create generalized models of plant responses.

AI image analysis↗
DOE OSTI2024

A genetic screen for dominant chloroplast reactive oxygen species signaling mutants reveals life stage-specific singlet oxygen signaling networks

Plants employ intricate molecular mechanisms to respond to abiotic stresses, which often lead to the accumulation of reactive oxygen species (ROS) within organelles such as chloroplasts. Such ROS can produce stress signals that regulate cellular response mechanisms. One ROS, singlet oxygen ( 1 O 2 ), is predominantly produced in the chloroplast during photosynthesis and can trigger chloroplast degradation, programmed cell death (PCD), and retrograde (organelle-to-nucleus) signaling. However, little is known about the molecular mechanisms involved in these signaling pathways or how many different signaling 1 O 2 pathways may exist. The Arabidopsis thaliana plastid ferrochelatase two (fc2) mutant conditionally accumulates chloroplast 1 O 2 , making fc2 a valuable genetic system for studying chloroplast 1 O 2 -initiated signaling. Here, we have used activation tagging in a new forward genetic screen to identify eight dominant fc2 activation-tagged (fas) mutations that suppress chloroplast 1 O 2 -initiated PCD. While 1 O 2 -triggered PCD is blocked in all fc2 fas mutants in the adult stage, such cellular degradation in the seedling stage is blocked in only two mutants. This differential blocking of PCD suggests that life-stage-specific 1 O 2 -response pathways exist. In addition to PCD, fas mutations generally reduce 1 O 2 -induced retrograde signals. Furthermore, fas mutants have enhanced tolerance to excess light, a natural mechanism to produce chloroplast 1 O 2 . However, general abiotic stress tolerance was only observed in one fc2 fas mutant (fc2 fas2). Together, this suggests that plants can employ general stress tolerance mechanisms to overcome 1 O 2 production but that this screen was mostly specific to 1 O 2 signaling. We also observed that salicylic acid (SA) and jasmonate (JA) stress hormone response marker genes were induced in 1 O 2 -stressed fc2 and generally reduced by fas mutations, suggesting that SA and JA signaling is correlated with active 1 O 2 signaling and PCD. Together, this work highlights the complexity of 1 O 2 signaling by demonstrating that multiple pathways may exist and introduces a suite of new 1 O 2 signaling mutants to investigate the mechanisms controlling chloroplast-initiated degradation, PCD, and retrograde signaling.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2003

Effects of heat stress on baroreflex function in humans

INTRODUCTION: Heat stress significantly reduces orthostatic tolerance in humans. The mechanism(s) causing this response remain unknown. The purpose of this review article is to present data pertaining to the hypothesis that reduced orthostatic tolerance in heat stressed individuals is a result of heat stress induced alterations in baroflex function. METHODS: In both normothermic and heat stressed conditions baroreflex responsiveness was assessed via pharmacological and non-pharmacological methods. In addition, the effects of heat stress on post-synaptic vasoconstrictor responsiveness were assessed. RESULTS: Generally, whole body heating did not alter baroreflex sensitivity defined as the gain of the linear portion of the baroreflex curve around the operating point. However, whole body heating shifted the baroreflex curve to the prevailing (i.e. elevated) heart rate and muscle sympathetic nerve activity. Finally, the heat stress impaired vasoconstrictor responses to exogenous administration of adrenergic agonists. CONCLUSION: Current data do not support the hypothesis that reduced orthostatic tolerance associated with heat stress in humans is due to impaired baroreflex responsiveness. This phenomenon may be partially due to the effects of heat stress on reducing vasoconstrictor responsiveness.

Review, Tutorial↗
NASA NTRS1983

Motion sickness - Acquisition and retention of adaptation effects compared in three motion environments

The acquisition and retention of adaptation effects in motion sickness was invetigated using a sudden-stop vestibulovisual interaction test for measuring susceptibility to motion sickness (Graybiel and Lackner, 1980). The test procedure included four successive assessments that provide not only an index of susceptibility to motion sickness but also the rates of acquisition and decay of adaptation effects. The 14 subjects who had participated in this test had previously served as subjects in parabolic flight experiments and seven of them had also taken part in the assessment of antimotion-sickness remedies in a slow rotation room. A study was conducted to determine whether these subjects' rates of acquisition and decay of adaptation to stressful motion represent consistent general features of their response across motion environments. It is found that an individual's rates of acquiring and losing adaptation are quite consistent in very different situations. In addition, the pattern of results indicate modifications of the sudden-stop vestibulovisual test that should increase its effectiveness as a motion-sickness screening procedure, both for orbital flight and for terrestrial conditions.

Graybiel, A.↗
NASA NTRS2000

Modal Response of Trapezoidal Wing Structures Using Second Order Shape Sensitivities

The modal response of wing structures is very important for assessing their dynamic response including dynamic aeroelastic instabilities. Moreover, in a recent study an efficient structural optimization approach was developed using structural modes to represent the static aeroelastic wing response (both displacement and stress). In this paper, the modal response of general trapezoidal wing structures is approximated using shape sensitivities up to the 2nd order. Also different approaches of computing the derivatives are investigated.

Liu, Youhua↗
NASA NTRS1984

Simplified analytical procedures for representing material cyclic response

Requirements for increased durability of gas turbine hot section structural components have made it necessary to place greater emphasis on accurate structural analysis and life prediction. Linear finite-element analysis is generally sufficient for structural analysis applications. However, for structures in the hot part of the engine, nonlinear structural analysis may be required under certain conditions for the accurate prediction of the local stress-strain response. Nonlinear finite element analysis represents a costly effort which is generally incompatible with the iterative nature of the design process. The present investigation is, therefore, concerned with two simplified procedures for estimating the local hysteretic response produced by cyclic thermal loading. These procedures reduce the need for nonlinear finite-element analysis.

Moreno, V.↗
DOE OSTI2022

Viscoelastic analysis of mussel threads reveals energy dissipative mechanisms

Mussels use byssal threads to secure themselves to rocks and as shock absorbers during cyclic loading from wave motion. Byssal threads combine high strength and toughness with extensibility of nearly 200%. Researchers attribute tensile properties of byssal threads to their elaborate multi-domain collagenous protein cores. Because the elastic properties have been previously scrutinized, we instead examined byssal thread viscoelastic behaviour, which is crucial for withstanding cyclic loading. By targeting protein domains in the collagenous core via chemical treatments, stress relaxation experiments provided insights on domain contributions and were coupled with in situ small-angle X-ray scattering to investigate relaxation-specific molecular reorganizations. Results show that when silk-like domains in the core were disrupted, the stress relaxation of the threads decreased by nearly 50% and lateral molecular spacing also decreased, suggesting that these domains are essential for energy dissipation and assume a compressed molecular rearrangement when disrupted. A generalized Maxwell model was developed to describe the stress relaxation response. The model predicts that maximal damping (energy dissipation) occurs at around 0.1 Hz which closely resembles the wave frequency along the California coast and implies that these materials may be well adapted to the cyclic loading of the ambient conditions.

36 MATERIALS SCIENCE↗
NASA NTRS2000

A Study of Influencing Factors on the Tensile Response of a Titanium Matrix Composite With Weak Interfacial Bonding

The generalized method of cells micromechanics model is utilized to analyze the tensile stress-strain response of a representative titanium matrix composite with weak interfacial bonding. The fiber/matrix interface is modeled through application of a displacement discontinuity between the fiber and matrix once a critical debonding stress has been exceeded. Unidirectional composites with loading parallel and perpendicular to the fibers are examined, as well as a cross-ply laminate. For each of the laminates studied, analytically obtained results are compared to experimental data. The application of residual stresses through a cool-down process was found to have a significant effect on the tensile response. For the unidirectional laminate with loading applied perpendicular to the fibers, fiber packing and fiber shape were shown to have a significant effect on the predicted tensile response. Furthermore, the interface was characterized through the use of semi-emperical parameters including an interfacial compliance and a "debond stress;" defined as the stress level across the interface which activates fiber/matrix debonding. The results in this paper demonstrate that if architectural factors are correctly accounted for and the interface is appropriately characterized, the macro-level composite behavior can be correctly predicted without modifying any of the fiber or matrix constituent properties.

Goldberg, Robert K.↗
NASA NTRS1987

STAEBL/general composites with hygrothermal effects (STAEBL/GENCOM)

A computer code has been developed to perform structural optimization of turbine blades made from angle ply fiber composite laminates. Design variables available for optimization include geometric parameters such as blade thickness distribution and root chord, and composite material parameters such as ply angles and numbers of plies of each constituent material. Design constraints include resonance margins, forced response margins, maximum stress, and maximum ply combined stress. A general description of this code is given. Design optimization studies for typical blades are presented.

Rubenstein, Robert↗
NASA NTRS1988

STAEBL/General composites with hygrothermal effects (STAEBL/GENCOM)

A computer code has been developed to perform structural optimization of turbine blades made from angle ply fiber composite laminates. Design variables available for optimization include geometric parameters such as blade thickness disribution and root chord, and composite material parameters such as ply angles and numbers of plies of each constituent material. Design constraints include resonance margins, forced response margins, maximum stress, and maximum ply combined stress. A general description of this code is given. Design optimization studies for typical blades are presented.

Rubinstein, R.↗
NASA NTRS1992

Tropical Pacific Ocean response to observed winds in a layered general circulation model

The effect of forcing by monthly wind-stress variability is assessed with respect to the behavior of an isopycnic coordinate general circulation model. The isopycnic model incorporates an embedded mixed layer, and the equations are given for the interior layers, the surface mixed layer, and the atmospheric forcing. The anomalous variability of several variables is examined in a simulation using data from 1970-1985 with specific attention given to the anomalous response related to the 1982-1983 ENSO. The model fields describing sea-surface temperature (SST), sea level, and currents are found to be comparable to those reported from observational campaigns. Anomalous values of SST compare best with observed data when averaged over large spatial regions, and the amplitudes of the mean horizontal currents and anomalous zonal currents are comparable except with respect to amplitude data. The present study permits the simulation of basin-scale tropical Pacific mixed-layer depth and the mean vertical velocity field.

Miller, Arthur J.↗
NASA NTRS1988

Structural correlates of imbibitional injury in Typha pollen

The ultrastructure of Typha latifolia pollen was examined as a function of pollen moisture content and incubation temperature, in order to identify possible lesions induced by imbibitional chilling. A syndrome of structural traits was found which characterizes damaged grains. Compared to viable grains, the protoplast of damaged pollen has a higher proportion of its volume occupied by vesicles, and less volume occupied by cytoplasm. Damaged grains also tend to have dilated cisternae of endoplasmic reticulum, larger starch grains and lipid bodies, poorly preserved mitochondria and membranes, and, sometimes, numerous electron-dense globules associated with membranes. The percentage of grains exhibiting this damage syndrome correlates closely with the number of ungerminated grains in most samples, regardless of moisture content or incubation temperature. Injury due to rapid imbibition from the dry state or to imbibitional chilling appear to be similar structurally, regardless of whether the stresses are imposed singly or together. The injury is not confined to one cell component (e.g., mitochondria), but may involve a generalized disruption of membranes. These results suggest that similar stress responses are elicited by imbibition from the dry state and by imbibitional chilling.

NASA Program Space Biology↗