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At least 469 records · Page 26

All sources NASA NTRS DOE OSTI

NASA NTRS2012

Compression After Impact on Honeycomb Core Sandwich Panels With Thin Facesheets: Experiments - Part 1

A two part research study has been completed on the topic of compression after impact (CAI) of thin facesheet honeycomb core sandwich panels. The research has focused on both experiments and analysis in an effort to establish and validate a new understanding of the damage tolerance of these materials. Part one, the subject of the current paper, is focused on the experimental testing. Of interest are sandwich panels, with aerospace applications, which consist of very thin, woven S2-fiberglass (with MTM45-1 epoxy) facesheets adhered to a Nomex honeycomb core. Two sets of specimens, which were identical with the exception of the density of the honeycomb core, were tested. Static indentation and low velocity impact using a drop tower are used to study damage formation in these materials. A series of highly instrumented CAI tests was then completed. New techniques used to observe CAI response and failure include high speed video photography, as well as digital image correlation (DIC) for full-field deformation measurement. Two CAI failure modes, indentation propagation, and crack propagation, were observed. From the results, it can be concluded that the CAI failure mode of these panels depends solely on the honeycomb core density.

McQuigg, Thomas D.↗

NASA NTRS2021

Reliability and Safety Assessment of Urban Air Mobility Concept Vehicles

The primary objective of this research effort is to identify failure modes and hazards associated with several configurations of multicopter concept vehicles supplied by NASA. Functional hazard analyses (FHA) and failure modes and effects criticality analyses (FMECA) are performed for each of the eight vehicle configurations under review. Conceptual design of notional powertrain configurations (turboshaft, electric, hybrid electric), notional thrust control systems (rpm control and collective control), and navigation control systems for the concept vehicles were to support the reliability and safety analysis and to assess whether a mission can be completed safely. Two kinds of analyses are performed: static safety analysis which enable the quantification of the likelihood of individual events, and dynamic safety analyses which allows the investigation of multiple time-dependent failures. Their objective is to quantify the likelihood of catastrophic failures.

Urban Air Mobility↗

DOE OSTI2023

Liquid hydrogen storage system for heavy duty trucks: Configuration, performance, cost, and safety

In this work, we investigate the potential of liquid hydrogen storage (LH 2 ) on-board Class-8 heavy duty trucks to resolve many of the range, weight, volume, refueling time and cost issues associated with 350 or 700-bar compressed H 2 storage in Type-3 or Type-4 composite tanks. We present and discuss conceptual storage system configurations capable of supplying H 2 to fuel cells at 5-bar with or without on-board LH 2 pumps. Structural aspects of storing LH 2 in double walled, vacuum insulated, and low-pressure Type-1 tanks are investigated. Structural materials and insulation methods are discussed for service at cryogenic temperatures and mitigation of heat leak to prevent LH 2 boiloff. Failure modes of the liner and shell are identified and analyzed using the regulatory codes and detailed finite element (FE) methods. The conceptual systems are subjected to a Failure modes and effects analysis (FMEA) and a safety, codes, and standards (SCS) review to rank failures and identify safety gaps. The results indicate that the conceptual systems can reach 19.6% usable gravimetric capacity, 40.9 g-H 2 /L usable volumetric capacity and $174-183/kg-H 2 cost (2016 USD) when manufactured 100,000 systems annually.

08 HYDROGEN↗

DOE OSTI2021

WhiteWind: White Etching Crack (WEC) Bearing Failures in Wind Turbine: Cooperative Research and Development, CRADA Number CRD-18-00758 (Final Report)

A WEC is a particularly aggressive, unpredictable and wide spread rolling element bearing failure mode that is common for large multi-megawatt (MW) wind turbines. WEC is considered the single most expensive failure mode for all wind turbine components, and there is currently no commercial solution. The Technical University of Denmark (DTU) is leading the WhiteWind project to investigate WECs through funding provided by the Innovation Fund Denmark. Other project partners include Vestas, SKF, Expanite, Rheinisch-Westfalische Technische Hochschule Aachen University (RWTH Aachen), and Argonne National Laboratory. The objective of the overall project is to develop a new surface engineered WEC-resistant bearing material using novel surface engineering techniques that shall provide a commercially competitive alternative to existing wind turbine bearings. NREL will support the project by providing existing measured bearing loads and validating models of drivetrain loads.

17 WIND ENERGY↗

NASA NTRS1995

Optimization of composite box-beam structures including effects of subcomponent interactions

Minimum mass designs are obtained for a simple box beam structure subject to bending, torque and combined bending/torque load cases. These designs are obtained subject to point strain and linear buckling constraints. The present work differs from previous efforts in that special attention is payed to including the effects of subcomponent panel interaction in the optimal design process. Two different approaches are used to impose the buckling constraints. When the global approach is used, buckling constraints are imposed on the global structure via a linear eigenvalue analysis. This approach allows the subcomponent panels to interact in a realistic manner. The results obtained using this approach are compared to results obtained using a traditional, less expensive approach, called the local approach. When the local approach is used, in-plane loads are extracted from the global model and used to impose buckling constraints on each subcomponent panel individually. In the global cases, it is found that there can be significant interaction between skin, spar, and rib design variables. This coupling is weak or nonexistent in the local designs. It is determined that weight savings of up to 7% may be obtained by using the global approach instead of the local approach to design these structures. Several of the designs obtained using the linear buckling analysis are subjected to a geometrically nonlinear analysis. For the designs which were subjected to bending loads, the innermost rib panel begins to collapse at less than half the intended design load and in a mode different from that predicted by linear analysis. The discrepancy between the predicted linear and nonlinear responses is attributed to the effects of the nonlinear rib crushing load, and the parameter which controls this rib collapse failure mode is shown to be the rib thickness. The rib collapse failure mode may be avoided by increasing the rib thickness above the value obtained from the (linear analysis based) optimizer. It is concluded that it would be necessary to include geometric nonlinearities in the design optimization process if the true optimum in this case were to be found.

Ragon, Scott A.↗

NASA NTRS2019

Reliability Requirements and Research Strategies for Urban Air Mobility Propulsion

An emerging new mission for aeronautics is Urban Air Mobility (UAM), a concept for air transportation around metropolitan areas with passenger-carrying operations. UAM vehicles must be capable of vertical take-off and landing, and this requirement presents unique technical challenges for electric and hybrid-based vertical take-off and landing (eVTOL). A critical challenge for UAM market growth is to gain public acceptance for being as safe as - or safer than - commercial air travel and automotive transportation. There is a lack of data for propulsion systems, components, and the associated thermal management systems for UAM eVTOL propulsion systems. The new mission, new propulsion system concepts, safety criticality of propulsion component performance during vertical take-off and lift operations, and lack of data presents many research challenges and opportunities. NASA has developed and published UAM vehicle concept studies. For a subset of the said concept vehicles, NASA has contracted for a study to identify failure modes and hazards associated with the propulsion systems of the concept vehicles and to perform functional hazard analyses (FHA) and failure modes and effects criticality analyses (FMECA) for each. From the completed study results, it was recommended for NASA to support research toward developing electric/hybrid-electric propulsion components with improved reliability and to explore powertrain architectures that can take advantage of higher reliability components to achieve inherent air-vehicle safety. NASA has started a research effort for UAM propulsion with a focus toward improving safety and reliability. Recent results and research strategy will be discussed toward the goals by means of: 1) improving individual component reliability through advanced materials and design methods, 2) improving the thermal management system, and 3) designing propulsion system architectures to provide inherent UAM vehicle safety.

Krantz, Timothy↗

NASA NTRSDate not supplied

What Went Wrong: A Survey of Wildfire UAS Mishaps through Named Entity Recognition

Increasingly, unmanned aircraft systems (UAS) are being applied to wildfire incidents for tasks such as mapping, aerial ignition, and delivery. As a result, incident reporting systems for wildfires are beginning to accumulate data related to UAS mishaps in wildfire response. In this research, we apply state-of-the-art natural language processing (NLP) techniques to develop a custom Named Entity Recognition (NER) model which extracts a Failure Modes and Effects Analysis (FMEA)-style survey of wildfire UAS mishaps reported in SAFECOM. The custom NER model is built by fine-tuning an existing (BERT) model, resulting in a generalizable NER model that can extract engineering relevant entities including failure modes, causes, effects, control processes, and recommendations from any failure-relevant text. Similar mishaps are clustered and reported as single rows within the FMEA. For each cluster, frequency, severity, and overall risk are computed. The methodology can be applied as part of a broader safety management system to track trends in mishaps and discover knowledge that can be utilized to improve safety outcomes and system performance.

Machine Learning↗

NASA NTRSDate not supplied

What Went Wrong: A Survey of Wildfire UAS Mishaps through Named Entity Recognition

Machine Learning↗

NASA NTRS2002

Non-Coalescence in Microgravity: Science and Technology

In this project we examine non-coalescence and non-wetting phenomena driven by either thermocapillary convection or forced motion of one surface relative to the other. In both cases, the non-coalescence or non-wetting is enabled by the existence of a lubricating layer of gas that exists to keep the two surfaces in question from coming into contact with one another. Recent progress has been made on several fronts: 1) measurement of the vibrational modes of pinned droplets; 2) development of an apparatus for the measurement of the frictional forces associated with a non-wetting droplet sliding over a solid surface; 3) measurements of the failure modes for non-wetting droplets and the influence of static electric charge on failure-, and 4) numerical simulation of a two-dimensional non-wetting droplet revealing a possible explanation for why the phenomenon has not been able to be observed using water as the droplet liquid. Issue 1) above is of relevance to the use of non-wetting droplets as positioning mechanisms and vibration dampers in a microgravity environment; issue 2) relates to the use of non-wetting droplets as nearly 'frictionless' bearings in low-load applications. Understanding of the failure modes identified in 3) is of importance to any potential application and the numerical simulations conducted under 4) allow us to obtain information about these systems that is currently not available through experimentation Each of these topics will be discussed briefly during the presentation.

Neitzel, G. Paul↗

NASA NTRS1984

Compression failure mechanisms in unidirectional composites

Compression failure mechanisms in unidirectional composites were examined. Possible failure modes of constituent materials are summarized and analytical models for fiber microbuckling are reviewed from a unified viewpoint. Due to deficiencies in available models, a failure model based on nonlinear properties and initial fiber curvature is proposed. The effect of constituent properties on composite compression behavior was experimentally investigated using two different graphite fibers and four different epoxy resins. The predominant microscopic scale failure mode was found to be shear crippling. In a soft resin, shear crippling was in the form of buckling of fibers on a microscopic scale. However, stiff resins failure was characterized by the formation of a kink band. For unidirectional laminates, compressive strength, and compressive modulus to a less extent, were found to increase with increasing magnitude of resin modulus. The change in compressive strength with resin modulus was predicted using the proposed nonlinear model.

Hahn, H. T.↗

NASA NTRS1986

Compression failure mechanisms in unidirectional composites

Hahn, H. T.↗

DOE OSTI2019

First-principles electronic structure in second-moment calculation of mode frequencies: Failure of quasiharmonic approximation in silicon

Using first-principles electronic structure calculations (local density approximation), we present second-moment calculations of the temperature dependence of the vibrational normal mode frequencies in Si up to 1500 K . The method is based on simple ensemble averages of displacements and forces and is easy to implement. These efficient calculations incorporate all interactions nonperturbatively, implicitly including all high order force constants, in contrast to typical perturbative approaches. Also in this work, we propose and apply to our classical calculations an estimated quantum correction that could be used for classical approaches other than the moments method. We compare our results to available experiments, including recent inelastic neutron scattering data and conclude that the second-moment gives the frequency shift to within a factor of 2 in contrast to quasiharmonic approaches that fail by an order of magnitude to predict the anharmonic shift. Noting the relative simplicity and speed of the calculations, we conclude that the second-moment approximation reasonably accounts for anharmonicity in a system that has been very closely studied experimentally and may reliably be applied in an exploratory way to more complex systems. Finally, we suggest that further improvement on the results could be obtained by incorporating the fourth moment, which can be implemented with little additional cost.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1981

The structures of the sintered plaque in the nickel hydroxide electrode

The various failure mechanisms were identified for the nickel electrode. The nickel sinter is involved in all these failure modes. The first one, chemical attack by carbonate, nitrate or other electrolyte components, involves corrosion of the nickel sinters. The second is the physical mode, which involves swelling of the electrode and physical shifting of the sinter in the electrodes. The third is the mechanical failure mode, and is due to fatigue or to the oxygen pressure that causes deformation or fracture of the sinter.

Vyas, B.↗

NASA NTRS1991

Linear quadratic servo control of a reusable rocket engine

A design method for a servo compensator is developed in the frequency domain using singular values. The method is applied to a reusable rocket engine. An intelligent control system for reusable rocket engines was proposed which includes a diagnostic system, a control system, and an intelligent coordinator which determines engine control strategies based on the identified failure modes. The method provides a means of generating various linear multivariable controllers capable of meeting performance and robustness specifications and accommodating failure modes identified by the diagnostic system. Command following with set point control is necessary for engine operation. A Kalman filter reconstructs the state while loop transfer recovery recovers the required degree of robustness while maintaining satisfactory rejection of sensor noise from the command error. The approach is applied to the design of a controller for a rocket engine satisfying performance constraints in the frequency domain. Simulation results demonstrate the performance of the linear design on a nonlinear engine model over all power levels during mainstage operation.

Musgrave, Jeffrey L.↗

NASA NTRS2018

Fatigue Life of a NiCr-Coated Powder Metallurgy Disk Superalloy After Varied Processing and Exposures

A protective ductile NiCr coating has shown promise to mitigate oxidation and corrosion attack on superalloy disk alloys. The effects of this coating on fatigue life and failure modes of the disk superalloy are an important concern. The objective of this study was to investigate the fatigue life and failure modes of disk superalloy specimens protected by this coating, using varied pre-coating and post-coating processes. Cylindrical gage fatigue specimens of a powder metallurgy-processed disk superalloy were grit blast or wet blast before being coated with a ductile NiCrY coating, then shot peened at low or medium levels after coating. All were then heat treated, some exposed, and finally all were subjected to fatigue at high temperature. The effects of varied pre-coating treatment, post-coating shot peening, and oxidation plus hot corrosion exposures on fatigue life with the coating were compared.

coating↗

NASA NTRS1986

Thermal barrier coating life prediction model

The objectives of this program are to determine the predominant modes of degradation of a plasma sprayed thermal barrier coating system, and then to develop and verify life prediction models accounting for these degradation modes. The program is divided into two phases, each consisting of several tasks. The work in Phase 1 is aimed at identifying the relative importance of the various failure modes, and developing and verifying life prediction model(s) for the predominant model for a thermal barrier coating system. Two possible predominant failure mechanisms being evaluated are bond coat oxidation and bond coat creep. The work in Phase 2 will develop design-capable, causal, life prediction models for thermomechanical and thermochemical failure modes, and for the exceptional conditions of foreign object damage and erosion.

Pilsner, B. H.↗

NASA NTRS2006

Air/Oil Seals R and D at AlliedSignal

AlliedSignal aerospace company is committed to significantly improving the reliabilities of air/oil seals in their gas turbine engines. One motivation for this is that aircraft cabin air quality can be affected by the performance of mainshaft air/oil seals. In the recent past, coking related failure modes have been the focus of air/oil seal R&D at AlliedSignal. Many significant advances have been made to combat coke related failures, with some more work continuing in this area. This years R&D begins to address other commin failure modes. Among them, carbon seal "blistering" has been a chronic problem facing the sealing industry for many decades. AlliedSignal has launched an aggressive effort this year to solve this problem for our aerospace rated carbon seals in a short (one to two year) timeframe. Work also continues in developing more user-friendly tools and data for seal analysis & design. Innovations in seal cooling continue. Nominally non-contacting hydropad sealing concept is being developed for aerospace applications. Finally, proprietary work is in planning stages for development of a seal with the aggressive aim of zero oil leakage.

Ullah, M. Rifat↗

NASA NTRSDate not supplied

Systems Health Monitoring: Integrating FMEA into Bayesian Networks

The foreseeable high traffic density suggests that a large number of electric propulsion systems will enter the airspace, and that they will also operate at high frequency, e.g., large number of take offs and landings per unit time. The reliability of such critical systems is therefore key to ensure high safety standards in the low-altitude airspace. Diagnostic systems, which aim at identifying incipient faults, can mitigate unexpected failures or lower-than-expected reliability by performing early fault detection by monitoring the systems. A key element of fault diagnosis is fault detection and isolation (FDI), which complexity increases with the complexity of the system itself, namely the number of subsystems and components, interactions among sub-systems, and the number of sensors available. The proposed approach leverages combination of failure mode and effect analysis (FMEA) integrated with Bayesian networks, thus introducing dependability structures into a diagnostic framework to aid FDI. Faults and failure events from the FMEA are mapped within a Bayesian network, where network edges replicate the links embedded within FMEAs. The integrated framework enables the fault isolation process by identifying the probability of occurrence of specific faults or root causes given evidence observed through sensor signals. In this work, sub systems of Urban Air Mobility (UAM) type vehicle like avionics, structures, power-train etc. are taken into account to show the approach at the system level. This work integrates early design phase in the development of UAM type vehicles with diagnostic tools, which are often developed later in the product life-cycle, or retrofitted at a later time on systems. Failure mode and effect analysis (FMEA) derived for the system in the design phase is embedded within a Bayesian network (BN).

UAM↗