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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Testing of containers made of glass-fiber reinforced plastic with the aid of acoustic emission analysis

Acoustic emission analysis as a quasi-nondestructive test method makes it possible to differentiate clearly, in judging the total behavior of fiber-reinforced plastic composites, between critical failure modes (in the case of unidirectional composites fiber fractures) and non-critical failure modes (delamination processes or matrix fractures). A particular advantage is that, for varying pressure demands on the composites, the emitted acoustic pulses can be analyzed with regard to their amplitude distribution. In addition, definite indications as to how the damages occurred can be obtained from the time curves of the emitted acoustic pulses as well as from the particular frequency spectrum. Distinct analogies can be drawn between the various analytical methods with respect to whether the failure modes can be classified as critical or non-critical.

Wolitz, K.↗
NASA NTRS1983

Failure mechanics in low-velocity impacts on thin composite plates

Eight-ply quasi-isotropic composite plates of Thornel 300 graphite in Narmco 5208 epoxy resin (T300/5208) were tested to establish the degree of equivalence between low-velocity impact and static testing. Both the deformation and failure mechanics under impact were representable by static indentation tests. Under low-velocity impacts such as tool drops, the dominant deformation mode of the plates was the first, or static, mode. Higher modes are excited on contact, but they decay significantly by the time the first-mode load reaches a maximum. The delamination patterns were observed by X-ray analysis. The areas of maximum delamination patterns were observed by X-ray analysis. The areas of maximum delamination coincided with the areas of highest peel stresses. The extent of delamination was similar for static and impact tests. Fiber failure damage was established by tensile tests on small fiber bundles obtained by deplying test specimens. The onset of fiber damage was in internal plies near the lower surface of the plates. The distribution and amount of fiber damage was similar fo impact and static tests.

Elber, W.↗
NASA NTRS1993

A numerical model for predicting crack path and modes of damage in unidirectional metal matrix composites

A finite element-based numerical technique has been developed to simulate damage growth in unidirectional composites. This technique incorporates elastic-plastic analysis, micromechanics analysis, failure criteria, and a node splitting and node force relaxation algorithm to create crack surfaces. Any combination of fiber and matrix properties can be used. One of the salient features of this technique is that damage growth can be simulated without pre-specifying a crack path. In addition, multiple damage mechanisms in the forms of matrix cracking, fiber breakage, fiber-matrix debonding and plastic deformation are capable of occurring simultaneously. The prevailing failure mechanism and the damage (crack) growth direction are dictated by the instantaneous near-tip stress and strain fields. Once the failure mechanism and crack direction are determined, the crack is advanced via the node splitting and node force relaxation algorithm. Simulations of the damage growth process in center-slit boron/aluminum and silicon carbide/titanium unidirectional specimens were performed. The simulation results agreed quite well with the experimental observations.

Bakuckas, J. G.↗
NASA NTRS1982

Graphite/polyimide technology overview and Space Shuttle Orbiter applications

The materials, production processes, testing procedures, and repair techniques for composite structures on the Orbiter are reviewed. The Orbiter currently features graphite/epoxy payload bay doors, as well as graphite/polyimide elevons, vertical tail, and aft body flap, which can withstand up to 600 F temperatures. Graphite/polyimide is also being considered for areas of the baseline aluminum structure and the thermal protection system in order to achieve a 20-30% weight reduction, i.e., over 7.5 tons. An analysis of the allowable stresses on FRC imide thermal protection system tiles bonded directly to the structure has shown satisfactory performances in high temperature and cryogenic conditions, although failure modes are yet to be determined. Ultrasonic emissions have been used for defect detection in nondestructive evaluations, together with tension, notch, shear, and compression tests. Field repairs have not been perfected, and require the evolution of high temperature adhesives that are curable under vacuum pressure and heat blankets.

Morita, W. H.↗
NASA NTRS1984

Application of Iosipescu specimen geometry to determination of shear strength in unidirectional composites

The Iosipescu (1967) test method, in conjunction with a finite element analysis of anisotropic, unidirectionally reinforced composite specimens, can be used to derive composite shear strength values despite the small size of the samples used. When such a specimen is loaded parallel to the fiber direction, fracture occurs by shear within a narrow region near the center of the specimen; this is consistent with the maximum shear area determined by finite element analysis. The resulting fracture surface, as observed, is characteristic of shear failure, occurring either within the matrix or at the fiber-matrix interface. Problems of compressive and mixed mode failure which accrue to short beam shear specimens are by the present method precluded.

Hurwitz, F. I.↗
NASA NTRS1988

Impact induced stresses, strains, and delaminations in composite plates

A method is presented for calculating the locations and sizes of delaminations which occur in a rectangular, fiber reinforced composite plate subjected to nonpenetrating (low velocity) impact of a solid object. The plate may be simply supported or clamped along its edges. In-plane loads or in-plane strains may be imposed on the plate during the impact. The method includes two steps. First, the stresses and strains in the plate are calculated by a three-dimensional, transient finite element method using 8-node brick elements with incompatible modes. Second, the locations, lengths, and widths of delaminations inside the plate are predicted by means of a proposed failure criterion, which is based on the concept of dimensional analysis. The finite element method and the failure criterion were implemented by a computer code which can be used to calculate the impactor position and velocity, the displacements of the plate, the stresses and strains inside the plate during the impact, and the locations and dimensions of the delaminations after the impact. Parametric studies were performed to illustrate the information which can be generated by the computer code.

Wu, Hsi-Yung T.↗
NASA NTRS2009

Towards Accelerated Aging Methodologies and Health Management of Power MOSFETs (Technical Brief)

Understanding aging mechanisms of electronic components is of extreme importance in the aerospace domain where they are part of numerous critical subsystems including avionics. In particular, power MOSFETs are of special interest as they are involved in high voltage switching circuits such as drivers for electrical motors. With increased use of electronics in aircraft control, it becomes more important to understand the degradation of these components in aircraft specific environments. In this paper, we present an accelerated aging methodology for power MOSFETs that subject the devices to indirect thermal overstress during high voltage switching. During this accelerated aging process, two major modes of failure were observed - latch-up and die attach degradation. In this paper we present the details of our aging methodology along with details of experiments and analysis of the results.

Celaya, Jose R.↗
NASA NTRS2014

Physics-Based Fragment Acceleration Modeling for Pressurized Tank Burst Risk Assessments

As part of comprehensive efforts to develop physics-based risk assessment techniques for space systems at NASA, coupled computational fluid and rigid body dynamic simulations were carried out to investigate the flow mechanisms that accelerate tank fragments in bursting pressurized vessels. Simulations of several configurations were compared to analyses based on the industry-standard Baker explosion model, and were used to formulate an improved version of the model. The standard model, which neglects an external fluid, was found to agree best with simulation results only in configurations where the internal-to-external pressure ratio is very high and fragment curvature is small. The improved model introduces terms that accommodate an external fluid and better account for variations based on circumferential fragment count. Physics-based analysis was critical in increasing the model's range of applicability. The improved tank burst model can be used to produce more accurate risk assessments of space vehicle failure modes that involve high-speed debris, such as exploding propellant tanks and bursting rocket engines.

Acceleration↗
DOE OSTI2026

Testing Recommendations for Thermal Failure Analysis

Minimizing ranges of uncertainty in failure QOIs is vital for making informed engineering decisions. To improve our decision-making ability, it is necessary to have a QOI representation that captures more complex failure modes. Capturing the physics of complex time-dependent temperature failure in explicit detail can be computationally and experimentally expensive. To avoid this blooming of complication and costs, an empirical QOI component-level failure/damage model may be sufficient to help identify component-level failure. In this context, failure and damage are abstractions of more complicated processes that lead to the cessation of normal operating behavior, not a representation of mechanical damage, such as void formation. Such a model requires minimal increases in computational cost and experimental burden. The proposed QOI serves as an indicator that something has likely failed, similar to the previous critical failure temperatures or pressures. This QOI will not replace any existing failure QOIs. It will be calculated alongside them, allowing for preservation of legacy style QOI measurements with new context from the new QOI.

36 MATERIALS SCIENCE↗
NASA NTRS1996

Risk/Requirements Trade-off Guidelines for Low Cost Satellite Systems

The accelerating trend toward faster, better, cheaper missions places increasing emphasis on the trade-offs between requirements and risk to reduce cost and development times, while still improving quality and reliability. The Risk/Requirement Trade-off Guidelines discussed in this paper are part of an integrated approach to address the main issues by focusing on the sum of prevention, analysis, control, or test (PACT) processes.

risk cost trade-offs failure modes↗
NASA NTRS1995

Gear Crack Propagation Investigation

Reduced weight is a major design goal in aircraft power transmissions. Some gear designs incorporate thin rims to help meet this goal. Thin rims, however, may lead to bending fatigue cracks. These cracks may propagate through a gear tooth or into the gear rim. A crack that propagates through a tooth would probably not be catastrophic, and ample warning of a failure could be possible. On the other hand, a crack that propagates through the rim would be catastrophic. Such cracks could lead to disengagement of a rotor or propeller from an engine, loss of an aircraft, and fatalities. To help create and validate tools for the gear designer, the NASA Lewis Research Center performed in-house analytical and experimental studies to investigate the effect of rim thickness on gear-tooth crack propagation. Our goal was to determine whether cracks grew through gear teeth (benign failure mode) or through gear rims (catastrophic failure mode) for various rim thicknesses. In addition, we investigated the effect of rim thickness on crack propagation life. A finite-element-based computer program simulated gear-tooth crack propagation. The analysis used principles of linear elastic fracture mechanics, and quarter-point, triangular elements were used at the crack tip to represent the stress singularity. The program had an automated crack propagation option in which cracks were grown numerically via an automated remeshing scheme. Crack-tip stress-intensity factors were estimated to determine crack-propagation direction. Also, various fatigue crack growth models were used to estimate crack-propagation life. Experiments were performed in Lewis' Spur Gear Fatigue Rig to validate predicted crack propagation results. Gears with various backup ratios were tested to validate crack-path predictions. Also, test gears were installed with special crack-propagation gages in the tooth fillet region to measure bending-fatigue crack growth. From both predictions and tests, gears with backup ratios (rim thickness divided by tooth height) of 3.3 and 1.0 produced tooth fractures, whereas a backup ratio of 0.3 produced rim fractures. For a backup ratio of 0.5, the experiments produced rim fractures and the predictions produced both rim and tooth fractures, depending on the initial geometry of the crack. Good correlation between predicted and measured crack growth was achieved when the fatigue crack-closure concept was introduced into the analysis. As the gear rim thickness decreased, the compressive cyclic stress in the gear-tooth fillet region increased. This retarded crack growth and increased the number of crack-propagation cycles to failure.

Source record↗
NASA NTRS1996

A 100 Hour Wear Test of the NASA NSTAR Ion Thruster

In a NASA program to validate 30 cm Xenon ion thruster technology for use in planetary missions a combination of analysis and testing is being used to establish engine reliability. Five long duration tests are planned to identify new failure mechanisms and characterize the parameters which drive known damage accumulation failure modes.

ion thruster NSTAR xenon ion propulsion ion propul↗
NASA NTRS2010

Ultra Reliable Closed Loop Life Support for Long Space Missions

Spacecraft human life support systems can achieve ultra reliability by providing sufficient spares to replace all failed components. The additional mass of spares for ultra reliability is approximately equal to the original system mass, provided that the original system reliability is not too low. Acceptable reliability can be achieved for the Space Shuttle and Space Station by preventive maintenance and by replacing failed units. However, on-demand maintenance and repair requires a logistics supply chain in place to provide the needed spares. In contrast, a Mars or other long space mission must take along all the needed spares, since resupply is not possible. Long missions must achieve ultra reliability, a very low failure rate per hour, since they will take years rather than weeks and cannot be cut short if a failure occurs. Also, distant missions have a much higher mass launch cost per kilogram than near-Earth missions. Achieving ultra reliable spacecraft life support systems with acceptable mass will require a well-planned and extensive development effort. Analysis must determine the reliability requirement and allocate it to subsystems and components. Ultra reliability requires reducing the intrinsic failure causes, providing spares to replace failed components and having "graceful" failure modes. Technologies, components, and materials must be selected and designed for high reliability. Long duration testing is needed to confirm very low failure rates. Systems design should segregate the failure causes in the smallest, most easily replaceable parts. The system must be designed, developed, integrated, and tested with system reliability in mind. Maintenance and reparability of failed units must not add to the probability of failure. The overall system must be tested sufficiently to identify any design errors. A program to develop ultra reliable space life support systems with acceptable mass should start soon since it must be a long term effort.

Jones, Harry W.↗
DOE OSTI2025

Micromechanical response of SiC-OPyC layers in TRISO fuel particles

Tristructural isotropic (TRISO)–coated particle fuel is a proposed fuel for multiple advanced reactor concepts. The performance of the particle depends on whether the silicon carbide (SiC) layer remains intact to prevent the release of metallic and gaseous fission products. Mechanical fracture of the SiC layer is a potential failure mode under various fuel configurations and operating environments, including the potential transmission of matrix-originating cracks through TRISO particles. Furthermore, this study uses instrumented indentation techniques on cross-sectioned surrogate particles to examine the mechanical stability of the critical interface between SiC and the outer pyrolytic carbon (OPyC) layer. The observed behavior at the interface is rationalized by examining the radially dependent fracture behavior of the SiC layer and performing a numerical analysis to quantify the residual stresses that develop during the processing and cross-sectioning of the as-fabricated particle. Characterizing the SiC-OPyC interface of surrogate TRISO particles using nanoindentation provides unique insight into the interface's room-temperature residual stress and mechanical stability. The modeling efforts were used to investigate the experimental procedure further, and the results are presented herein to validate this fuel form's potential mechanical failure modes.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1980

Microstructural characterization of the HRSI thermal protection system for space shuttle

Components of the space shuttle high temperature reusable surface insulation (HRSI) system were microscopically characterized, both separately and as a system, to obtain information needed for stress analysis models of the thermal protection system. A tension specimen of the HRSI system was loaded in steps and was microscopically observed at each load condition to demonstrate the tension failure mode associated with strain isolation pad (SIP) behavior. A local failure occurred which should be associated with transfer of load through transverse fibers in the SIP. Stress concentrations attributed to the SIP behavior necessitated strengthening of the HRSI by densification of the RSI at the bondline. An HRSI tile was microscopically characterized after the densification process. The densified surface layer blended into the RSI which caused a gradual change in density. The gradation in density does not appear to represent a sharp discontinuity in elastic modulus between the densified layer and the parent material.

Ransone, P. O.↗
DOE OSTI2023

Energy in the Balance: PV Reliability to Power the Energy Transition

We present an analysis of the effects of reliability on our ability to achieve the energy transition deployment targets. We examine three end of life modes as captured in the PV ICE tool; degradation, failures, and project lifetime. Recommendations are made for improving PV reliability for achieving energy energy transition.

circularity↗
DOE OSTI2024

Microstructural characterization and equibiaxial flexural strength of CeO 2 and Ti-doped CeO 2

In this study, the synthesis of CeO 2 and titanium dioxide (TiO 2 ) doped CeO 2 (TDC) monoliths are investigated, and their fracture strength is assessed using an equibiaxial flexure testing technique at room temperature. Pellets were synthesized using conventional powder processing and sintering methods to produce the desired characteristics. The TiO 2 dopant concentration was optimized at 0.1 wt % TiO 2 to obtain dense, solid-solution pellets with an enhanced grain microstructure. A ball-on-ring fixture was used to obtain the TRS and Weibull parameters of over 30 pellets for CeO 2 and 0.1 wt % TDC to compare fracture behavior. The TRS of CeO 2 pellets ranged from 88 to 160 MPa and the TRS of 0.1 wt % TDC pellets ranged from 102 to 171 MPa, both being consistent with published values. Weibull parameters, such as characteristic strength and Weibull modulus, were extracted as 129 MPa and 8.5 for CeO 2 and 150 MPa and 9.3 for 0.1 wt % TDC, respectively. Although Hertzian contact damage was observed on compressive surfaces, failure initiation occurred on the tensile surfaces of both types of samples. Fracture surface analysis for CeO 2 indicated a predominantly intergranular fracture while 0.1 wt % TDC had a predominantly transgranular fracture mode. Finally, the TRS of 0.1 wt % TDC resulted in increased Weibull parameters when compared to CeO 2 , indicating sample chemistry and microstructure impact mechanical behavior for these samples.

36 MATERIALS SCIENCE↗