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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Characterization of long-term extension of isolated cell walls from growing cucumber hypocotyls

Walls from frozen-thawed cucumber (Cucumis sativus L.) hypocotyls extend for many hours when placed in tension under acidic conditions. This study examined whether such "creep" is a purely physical process dependent on wall viscoelasticity alone or whether enzymatic activities are needed to maintain wall extension. Chemical denaturants inhibited wall creep, some acting reversibly and others irreversibly. Brief (15 s) boiling in water irreversibly inhibited creep, as did pre-incubation with proteases. Creep exhibited a high Q10 (3.8) between 20 degrees and 30 degrees C, with slow inactivation at higher temperatures, whereas the viscous flow of pectin solutions exhibited a much lower Q10 (1.35). On the basis of its temperature sensitivity, involvement of pectic gel-sol transitions was judged to be of little importance in creep. Pre-incubation of walls in neutral pH irreversibly inactivated their ability to creep, with a half-time of about 40 min. At 1 mM, Cu2+, Hg2+ and Al3+ were strongly inhibitory whereas most other cations, including Ca2+, had little effect. Sulfhydryl-reducing agents strongly stimulated creep, apparently by stabilizing wall enzyme(s). The physical effects of these treatments on polymer interactions were examined by Instron and stress-relaxation analyses. Some treatments, such as pH and Cu2+, had significant effects on wall viscoelasticity, but others had little or no apparent effect, thus implicating an enzymatic creep mechanism. The results indicate that creep depends on relatively rugged enzymes that are firmly attached to or entangled in the wall. The sensitivity of creep to SH-reducing agents indicates that thiol reduction of wall enzymes might provide a control mechanism for endogenous cell growth.

NASA Program Space Biology↗
NASA NTRS1989

Mechanism of gibberellin-dependent stem elongation in peas

Stem elongation in peas (Pisum sativum L.) is under partial control by gibberellins, yet the mechanism of such control is uncertain. In this study, we examined the cellular and physical properties that govern stem elongation, to determine how gibberellins influence pea stem growth. Stem elongation of etiolated seedlings was retarded with uniconozol, a gibberellin synthesis inhibitor, and the growth retardation was reversed by exogenous gibberellin. Using the pressure probe and vapor pressure osmometry, we found little effect of uniconozol and gibberellin on cell turgor pressure or osmotic pressure. In contrast, these treatments had major effects on in vivo stress relaxation, measured by turgor relaxation and pressure-block techniques. Uniconozol-treated plants exhibited reduced wall relaxation (both initial rate and total amount). The results show that growth retardation is effected via a reduction in the wall yield coefficient and an increase in the yield threshold. These effects were largely reversed by exogenous gibberellin. When we measured the mechanical characteristics of the wall by stress/strain (Instron) analysis, we found only minor effects of uniconozol and gibberellin on the plastic compliance. This observation indicates that these agents did not alter wall expansion through effects on the mechanical (viscoelastic) properties of the wall. Our results suggest that wall expansion in peas is better viewed as a chemorheological, rather than a viscoelastic, process.

NASA Discipline Plant Biology↗
NASA NTRS1988

Growth inhibition, turgor maintenance, and changes in yield threshold after cessation of solute import in pea epicotyls

The dependence of stem elongation on solute import was investigated in etiolated pea seedlings (Pisum sativum L. var Alaska) by excising the cotyledons. Stem elongation was inhibited by 60% within 5 hours of excision. Dry weight accumulation into the growing region stopped and osmotic pressure of the cell sap declined by 0.14 megapascal over 5 hours. Attempts to assay phloem transport via ethylenediaminetetraacetate-enhanced exudation from cut stems revealed no effect of cotyledon excision, indicating that the technique measured artifactual leakage from cells. Despite the drop in cell osmotic pressure, turgor pressure (measured directly via a pressure probe) did not decline. Turgor maintenance is postulated to occur via uptake of solutes from the free space, thereby maintaining the osmotic pressure difference across the cell membrane. Cell wall properties were measured by the pressure-block stress relaxation technique. Results indicate that growth inhibition after cotyledon excision was mediated primarily via an increase in the wall yield threshold.

NASA Discipline Number 40-30↗
NASA NTRS1997

Assembly and enlargement of the primary cell wall in plants

Growing plant cells are shaped by an extensible wall that is a complex amalgam of cellulose microfibrils bonded noncovalently to a matrix of hemicelluloses, pectins, and structural proteins. Cellulose is synthesized by complexes in the plasma membrane and is extruded as a self-assembling microfibril, whereas the matrix polymers are secreted by the Golgi apparatus and become integrated into the wall network by poorly understood mechanisms. The growing wall is under high tensile stress from cell turgor and is able to enlarge by a combination of stress relaxation and polymer creep. A pH-dependent mechanism of wall loosening, known as acid growth, is characteristic of growing walls and is mediated by a group of unusual wall proteins called expansins. Expansins appear to disrupt the noncovalent bonding of matrix hemicelluloses to the microfibril, thereby allowing the wall to yield to the mechanical forces generated by cell turgor. Other wall enzymes, such as (1-->4) beta-glucanases and pectinases, may make the wall more responsive to expansin-mediated wall creep whereas pectin methylesterases and peroxidases may alter the wall so as to make it resistant to expansin-mediated creep.

NASA Discipline Plant Biology↗
NASA NTRS2004

Vectran Fiber Time-Dependent Behavior and Additional Static Loading Properties

Vectran HS appears from literature and testing to date to be an ideal upgrade from Kevlar braided cords for many long-term, static-loading applications such as tie-downs on solar arrays. Vectran is a liquid crystalline polymer and exhibits excellent tensile properties. The material has been touted as a zero creep product. Testing discussed in this report does not support this statement, though the creep is on the order of four times slower than with similar Kevlar 49 products. Previous work with Kevlar and new analysis of Vectran testing has led to a simple predictive model for Vectran at ambient conditions. The mean coefficient of thermal expansion (negative in this case) is similar to Kevlar 49, but is not linear. A positive transition in the curve occurs near 100 C. Out-gassing tests show that the material performs well within parameters for most space flight applications. Vectran also offers increased abrasion resistance, minimal moisture regain, and similar UV degradation. The effects of material construction appear to have a dramatic effect in stress relaxation for braided Vectran. To achieve the improved relaxation rate, upgrades must also examine alternate construction or preconditioning methods. This report recommends Vectran HS as a greatly improved replacement material for applications where time-dependent relaxation is a major factor.

Fette, Russell B.↗
NASA NTRS1996

Composite prepreg application device

A heated shoe and cooled pressure roller assembly for composite prepreg application is provided. The shoe assembly includes a heated forward contact surface having a curved pressure surface. The following cooled roller provides a continuous pressure to the thermoplastic while reducing the temperature to approximately 5.degree. C. below glass transition temperature. Electric heating coils inside the forward portion of the shoe heat a thermoplastic workpiece to approximately 100.degree. C. above the glass transition. Immediately following the heated contact surface, a cooled roller cools the work. The end sharpened shape of the heated shoe trailing edge tends to prevent slag buildup and maintain a uniform, relaxed stress fabrication.

Sandusky, Donald A.↗
NASA NTRS2010

Grain Boundary Engineering the Mechanical Properties of Allvac 718Plus(Trademark) Superalloy

Grain Boundary Engineering can enhance the population of structurally-ordered "low S" Coincidence Site Lattice (CSL) grain boundaries in the microstructure. In some alloys, these "special" grain boundaries have been reported to improve overall resistance to corrosion, oxidation, and creep resistance. Such improvements could be quite beneficial for superalloys, especially in conditions which encourage damage and cracking at grain boundaries. Therefore, the effects of GBE processing on high-temperature mechanical properties of the cast and wrought superalloy Allvac 718Plus (Allvac ATI) were screened. Bar sections were subjected to varied GBE processing, and then consistently heat treated, machined, and tested at 650 C. Creep, tensile stress relaxation, and dwell fatigue crack growth tests were performed. The influences of GBE processing on microstructure, mechanical properties, and associated failure modes are discussed.

Gabb, Timothy P.↗
NASA NTRS2014

Design Curve Generation for 3D SiC Fiber Architecture

The design tool provides design curves that allow a simple and quick way to examine multiple factors that can influence the processing and key properties of the preforms and their final SiC-reinforced ceramic composites without over obligating financial capital for the fabricating of materials. Tool predictions for process and fiber fraction properties have been validated for a HNS 3D preform.The virtualization aspect of the tool will be used to provide a quick generation of solid models with actual fiber paths for finite element evaluation to predict mechanical and thermal properties of proposed composites as well as mechanical displacement behavior due to creep and stress relaxation to study load sharing characteristic between constitutes for better performance.Tool predictions for the fiber controlled properties of the SiCSiC CMC fabricated from the HNS preforms will be valuated and up-graded from the measurements on these CMC

matrix materials↗
NASA NTRS2015

Development of an Ablative 3D Quartz / Cyanate Ester Composite for the Orion Spacecraft Compression Pad

With the successful flight test of the Orion Multipurpose Crew Vehicle last December, NASA is well on its way to sending humans into deep space with the ultimate goal of putting astronauts on Mars in the 2030s. Orion will receive some upgrades for its next launch in 2018 including a newly developed 3D quartz / cyanate ester composite material for the compression pad. Multiple pad locations in the heat shield serve as a part of the mechanism for holding the Crew and Service Modules together during most mission phases prior to separation followed by Earth re-entry of the Crew Module. Thus the compression pad must survive structural and aerothermal loads, and protect the adjascent structure and heat shield materials from over-heating.This paper describes the approach used for developing the new 3D composite, including continuous 3D weaving on an automated loom followed by resin transfer molding. Mechanical, thermal, arc jet ,and stress relaxation testing of the 3D composite are also described.

Feldman, Jay D.↗
NASA NTRSDate not supplied

Py MILab: Capturing, Analyzing and Storing Test Data

Integrated Computational Materials Engineering (ICME) has recently received widespread attention due to its promises in reducing dependence on physical testing for engineering design by relying on simulation, reducing both time and cost to market for various applications. ICME however requires validated multiscale material models, which is heavily dependent on available test data with full material and test pedigree, including material processing, test and measurement equipment, raw data collection, and analysis methodology and results. Populating searchable information management systems with such rich data sets is often burdensome for data producers, resulting in a lack of findable data for modelers to validate and verify their models. To overcome these cultural barriers to ICME, NASA has developed of various database-integration toolsets that perform both data management activities within the organization’s best practices with additional functionality that relieves the effort of the data producer and promotes adoption of information management system. One such tool currently under development is Py MILab, an automatic framework for automatic capturing, analysis, maintenance, and storage of material test data. Py MILab uses a modular approach for capturing raw data, analyzing the data, and storing the data in a database, interfaced by neutral file structures, to promote plug-and-play capabilities for various analysis types. TMAnalysis is a Python-based tool that performs automatic data reduction and analysis of uniaxial thermomechanical test data. The TMAnalysis toolset can be implemented within the Analysis module of Py MILab, and thus requires a populated neutral file form the Raw Data Module of Py MILab and outputs a Analysis neutral file compatible with the Database Module of Py MILab. TMAnalysis is able to perform automatic segmentation of multistage tests and perform data analysis and reduction, including determination of point-wise properties in tension, compression, and shear, analysis of stress relaxation tests, creep analysis and zone identification, and combination of these stage types for tests with complex loading histories. The TMAnalysis code is accompanied with a graphical user interface (GUI) that allows users to easily analyze test data in bulk, verify the automatic, consistent analysis performed by the backend code, and edit stage segmentation if necessary before producing the output neutral files, ensuring data is properly analyzed and maintained with full traceability.

Data management↗
DOE OSTI2023

Update on the Current R&D Activity in the U.S.

This presentation is to fulfil DOE commitment to GIF VHTR Materials PMB. Notched creep rupture testing: Weldment V-notch specimen test finished. 800C 60MPa, 15,716 hour rupture life. Two double V-notch specimen tests have finished. Crack growth tests: System modification was required for creep and creep-fatigue testing, Epsilon 3548COD Extensometer has been ordered, to allow load-line displacement measurements, to be paired with direct current potential drop already used to measure crack length, Sample redesigned in accordance to ASTM E2760 and E1457 to allow for both creep and creep-fatigue crack growth rate testing. Alloy 800H Weldments (1/2) and Alloy 800H Weldments (2/2), Variable Fatigue Testing, and Multi=axial Stress Relaxation. Continue work to finish 800H model, examine ?universal? constitutive model form.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

FY23 status report on the development of new ASME Section III, Division 5 Class B rules

This report summarizes the work done in Fiscal Year 2023 on the development of the new American Society of Mechanical Engineers Boiler and Pressure Vessel Code, Section III, Division 5, Class B rules to address the gaps identified for high temperature reactor designs. The summary of the design-by-analysis strain limit evaluation and creep-fatigue damage assessment is presented. The proposed design-by-analysis creep-fatigue damage calculation approach uses a new elastic follow-up-based Isochronous Stress Strain Curve stress relaxation procedure. This approach captures the elastic follow-up generated due to interactions of components with adjacent components, supports, and other connections in the power plant. A set of sample problems are selected to validate the proposed design-by-analysis rules for creep-fatigue damage assessment. The proposed Class B rules are evaluated against the Class A elastic design rules, and the experimental data obtained from a family of Simplified Model Test based key-feature test results. The proposed Class B creep-fatigue damage assessment methodology yields conservative design cycles estimates compared to the experimental results.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2024

Evaluation of proposed Section III Division 5 Class B rules: Piping example problem

Evaluation of proposed Section III Division 5 Class B rules: Piping example problem to be presented include Z pipe geometry and model problem statement, Z pipe loads and design inputs problem statement, Primary Stress Limit overview, Primary stress limit pseudo yield stress calculation, Primary stress limited factored load procedure, Strain limit evaluation composite load cycle, Strain limit evaluation pseudo yield stress, Strain limit evaluation strain limit criteria and ratcheting check, Creep fatigue damage evaluation overview, Creep fatigue damage evaluation alternating stress calculations, Creep fatigue damage evaluation lower bound stress, Creep fatigue damage evaluation stress relaxation history, Creep fatigue damage evaluation damage fractions, and Recommendations to consider for Z-pipe problem.

42 ENGINEERING↗
DOE OSTI2024

Mechanical Response of Cr-Coated Zircaloy-4 Cladding to Pellet-Cladding Interactions

Chromium-coated zircaloy is a promising accident tolerant fuel (ATF) cladding design which can help mitigate high temperature oxidation. The mechanical response of the cladding during and after loading may be altered by the Cr coating throughout anticipated operational and accident occurrences such as a pellet-cladding interaction (PCI). In this work, the mechanical behavior of Cr-coated and uncoated cold worked stress-relieved (CWSR) Zircaloy-4 (Zry-4) cladding to PCI loading conditions are studied. Stress relaxation tests are performed on CWSR Zry-4 cladding using full-tube axial tension and internal pressurization to investigate mechanical anisotropy and rate-limiting deformation mechanisms of the uncoated Zry-4. These results are compared to internal pressure testing results of similar cladding with physical vapor deposition (PVD) Cr-coating to reveal how the Cr-coating affects the cladding mechanical response. Findings are discussed in the context of ATF cladding performance during operation and storage.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗