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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Research Infusion Collaboration: Finding Defect Patterns in Reused Code

The 'Finding Defect Patterns in Reused Code' Research Infusion Collaboration was performed by Jet Propulsion Laboratory/Caltech under Contract 104-07-02.679 102 197 08.14.4. This final report describes the collaboration and documents the findings, including lessons learned.The research infusion collaboration characterized, using Orthogonal Defect Classification, defect reports for code that will be reused in mission-critical software on Deep Space Network Antenna controllers. Code reuse is estimated to be 90%, so it is important to identify systemic defects, or patterns, prior to reuse of this code. The work also identified ways to avoid certain types of defects and to test more efficiently.The primary objectives of the project were:to analyze defect patterns of the code to be reused based on the defects'Orthogonal Defect Classification (ODC)and to achieve a successful infusion of ODC to a project.

orthogonal defect classification (ODC)↗
NASA NTRS2002

Evolutionary Design of a Robotic Material Defect Detection System

During the post-flight inspection of SSME engines, several inaccessible regions must be disassembled to inspect for defects such as cracks, scratches, gouges, etc. An improvement to the inspection process would be the design and development of very small robots capable of penetrating these inaccessible regions and detecting the defects. The goal of this research was to utilize an evolutionary design approach for the robotic detection of these types of defects. A simulation and visualization tool was developed prior to receiving the hardware as a development test bed. A small, commercial off-the-shelf (COTS) robot was selected from several candidates as the proof of concept robot. The basic approach to detect the defects was to utilize Cadmium Sulfide (CdS) sensors to detect changes in contrast of an illuminated surface. A neural network, optimally designed utilizing a genetic algorithm, was employed to detect the presence of the defects (cracks). By utilization of the COTS robot and US sensors, the research successfully demonstrated that an evolutionarily designed neural network can detect the presence of surface defects.

Ballard, Gary↗
NASA NTRS1974

Cytogenic studies of blood (experiment M111)

The Skylab M111 experiment was a continuation of the preflight and postflight chromosomal analyses of the flight crews that have been performed since the Gemini 3 mission. The experiment was designed to determine whether some space flight parameter produces cytogenetic effects in human cells and to provide biological radiation dosimetric capability in the event of significant radiation exposure to a flight crew. On each of the Skylab flights, blood lymphocytes for analysis of chromosomes for structural defects were obtained from each of the prime crewmembers and from a ground-based control group before and after flight. Two types of defects were recorded. The minor defects included the following aberrations: chromatid fragments, chromosome fragments, and deletions. Structural rearrangements such as dicentrics, exchanges, ring chromosomes, and translocations were photographed, and the cells were karyotyped to delineate, when possible, the chromosome or chromosomes involved in the rearrangement. Result seems to indicate that the flight itself was not a major contributing factor.

Lockhart, L. H.↗
NASA NTRS1974

SEM evaluation of metallization on semiconductors

A test method for the evaluation of metallization on semiconductors is presented and discussed. The method has been prepared in MIL-STD format for submittal as a proposed addition to MIL-STD-883. It is applicable to discrete devices and to integrated circuits and specifically addresses batch-process oriented defects. Quantitative accept/reject criteria are given for contact windows, other oxide steps, and general interconnecting metallization. Figures are provided that illustrate typical types of defects. Apparatus specifications, sampling plans, and specimen preparation and examination requirements are described. Procedures for glassivated devices and for multi-metal interconnection systems are included.

Fresh, D. L.↗
NASA NTRS1974

Influence of material quality and process-induced defects on semiconductor device performance and yield

An overview of major causes of device yield degradation is presented. The relationships of device types to critical processes and typical defects are discussed, and the influence of the defect on device yield and performance is demonstrated. Various defect characterization techniques are described and applied. A correlation of device failure, defect type, and cause of defect is presented in tabular form with accompanying illustrations.

Porter, W. A.↗
NASA NTRS1989

Screening of metal matrix composites using ultrasonic C-scans

Ultrasonic C-scans can be used to find some types of defects in continuous fiber-reinforced metal matrix composites such as boron/aluminum composites. These defects are related to the fatigue behavior and fracture location of each inspected specimen. The C-scan technique determined the relative amount of defects in boron/aluminum composites. The defects were primarily identified as gaps in the fiber spacing. Those specimens with higher defect densities had shorter fatigue lives, lower fatigue endurance limits, and greater reductions in the elastic unloading modulus (that is, stiffness) because of fatigue cycling. This type of data could be used to set accept/reject levels for a composite panel based on C-scan indications.

Johnson, W. S.↗
NASA NTRS1990

Defect sensitivity of filament-wound structures in compression

Compression testing of 12-ply graphite/bismaleimide laminated plates with induced and natural defects is discussed, and emphasis is placed on resultant changes in strength and stiffness. Ply drops, ply cuts, and fiber crossovers are studied by comparison with a quasi-isotropic control group. It is observed that, as expected, failure initiates at the defects and progresses via delamination, sublaminate buckling, angle-ply cracking, and longitudinal ply failure. The ultimate stress is reduced by approximately 40 percent for all types of defects except the unsymmetrical cut-ply specimens which averages a 54-percent reduction. The average stiffness reduction of 10 percent is observed for specimens with induced defects. Fiber crossovers are found to reduce the laminate strength and stiffness significantly.

Jensen, David W.↗
NASA NTRS2017

Development and Validation of NDE Standards for NASA’s Advanced Composites Project

The adoption of composite materials in aircraft manufacturing for use in structural applications continues to increase but is still relatively new to the industry. Composite components have large development and certification costs in comparison to metallic structures. Traditional methods of nondestructive evaluation (NDE) used for isotropic materials such as metals may not be adequate for composite applications and therefore is a contributing factor to the cost and complexity of developing new structural composites. Additionally, the defects of interest in composite materials are significantly different from metals. Thus, good quality composite reference standards are essential to obtaining reliable and quantifiable NDE results. Ideally, reference standards contain flaws or damage whose NDE indications most closely represent those created by actual flaws/damage. They should also be easy to duplicate and inexpensive to manufacture. NASA’s Advanced Composites Project, working with industry partners, developed a set of composite standards that contain a range of validated defects representing those typically found in aerospace composite materials. This paper will provide an overview of the standards fabricated, the manufacturing plans used to fabricate them, the types of defects included, and validation testing that has performed. Also discussed is an inter-laboratory “round-robin” test that is being performed on these standards. The paper will describe a guidance document being compiled to outline relevant inspection procedures for challenging and critical defects unique to composites where conventional techniques may not be appropriate.

Cramer, K. Elliott↗
NASA NTRS1972

Evaluation of nondestructive testing techniques for the space shuttle nonmetallic thermal protection system

A program was conducted to evaluate nondestructive analysis techniques for the detection of defects in rigidized surface insulation (a candidate material for the Space Shuttle thermal protection system). Uncoated, coated, and coated and bonded samples with internal defects (voids, cracks, delaminations, density variations, and moisture content), coating defects (holes, cracks, thickness variations, and loss of adhesion), and bondline defects (voids and unbonds) were inspected by X-ray radiography, acoustic, microwave, high-frequency ultrasonic, beta backscatter, thermal, holographic, and visual techniques. The detectability of each type of defect was determined for each technique (when applicable). A possible relationship between microwave reflection measurements (or X-ray-radiography density measurements) and the tensile strength was established. A possible approach for in-process inspection using a combination of X-ray radiography, acoustic, microwave, and holographic techniques was recommended.

Tiede, D. A.↗
NASA NTRS1983

Observation of defects in mercury cadmium telluride crystals grown by chemical vapor transport

A mixture of nitric and hydrochloric acids was found to yield etch pits on mercury cadmium telluride crystals grown by chemical vapor transport using iodine or mercuric iodide as the transport agent. Two types of pits were observed by optical microscopy: triangular pyramidal and round saucer shaped pits. Transmission electron microscopy confirmed that two types of defects were present: dislocations and second phase occlusions. The present study suggests that the defects are near the crystal surface and therefore will probably not significantly affect the electrical characteristics.

Irene, E. A.↗
NASA NTRS1989

Improved defect analysis of Gallium Arsenide solar cells using image enhancement

A new technique has been developed to capture, digitize, and enhance the image of light emission from a forward biased direct bandgap solar cell. Since the forward biased light emission from a direct bandgap solar cell has been shown to display both qualitative and quantitative information about the solar cell's performance and its defects, signal processing techniques can be applied to the light emission images to identify and analyze shunt diodes. Shunt diodes are of particular importance because they have been found to be the type of defect which is likely to cause failure in a GaAs solar cell. The presence of a shunt diode can be detected from the light emission by using a photodetector to measure the quantity of light emitted at various current densities. However, to analyze how the shunt diodes affect the quality of the solar cell the pattern of the light emission must be studied. With the use of image enhancement routines, the light emission can be studied at low light emission levels where shunt diode effects are dominant.

Kilmer, Louis C.↗
DOE OSTI2025

Static and dynamic topological defects in the domain textures in the helical antiferromagnet Ni 2 ⁢CoTeO 6

Real-space Bragg coherent x-ray-diffractive imaging unveils the formation of bubble and stripe antiferromagnetic (AFM) phase domains on the surface of Ni 2 ⁢CoTeO 6 single crystal. The stripe domains exhibit dislocation-type topological defects. The defects typically form as defect-antidefect pairs and can be created or annihilated by temperature changes and local heating. Thermal fluctuations of the AFM domain walls are observed near the Néel temperature. Topological defect pairs dynamically form and disappear in the fluctuating state. These observations provide a real-space perspective on the dynamics of the AFM phase transition in a helical antiferromagnet. Finally, the remarkable tunability of AFM domain walls in a helical antiferromagnet underscores their potential for AFM spintronics applications.

36 MATERIALS SCIENCE↗
NASA NTRS1979

Influence of alignment and surface defects on the performance of X-ray telescopes

The effects of misalignment and surface deformations on the image quality of a grazing incidence telescope with six nested subsystems are investigated. The axial rms-spot size serves as a measure for the image quality. The surface deformations are simulated by ellipsoidal and sinusoidal deviations from the ideal surface. Misalignments are tilts, decenters, and despaces of the individual elements. The effects of each type of defect are analyzed in a single two-element system. The full nested system is then analyzed in the presence of all possible defects on all 12 elements, whereby the magnitude of the defects is randomized within a given upper limit.

Korsch, D.↗
NASA NTRS2002

Scanning Electron Microscope Mapping System Developed for Detecting Surface Defects in Fatigue Specimens

An automated two-degree-of-freedom specimen positioning stage has been developed at the NASA Glenn Research Center to map and monitor defects in fatigue specimens. This system expedites the examination of the entire gauge section of fatigue specimens so that defects can be found using scanning electron microscopy (SEM). Translation and rotation stages are driven by microprocessor-based controllers that are, in turn, interfaced to a computer running custom-designed software. This system is currently being used to find and record the location of ceramic inclusions in powder metallurgy materials. The mapped inclusions are periodically examined during interrupted fatigue experiments. The number of cycles to initiate cracks from these inclusions and the rate of growth of initiated cracks can then be quantified. This information is necessary to quantify the effect of this type of defect on the durability of powder metallurgy materials. This system was developed with support of the Ultra Safe program.

Bonacuse, Peter J.↗
DOE OSTI2024

Sub-millisecond keyhole pore detection in laser powder bed fusion using sound and light sensors and machine learning

Laser powder bed fusion is a mainstream additive manufacturing technology widely used to manufacture complex parts in prominent sectors, including aerospace, biomedical, and automotive industries. However, during the printing process, the presence of an unstable vapor depression can lead to a type of defect called keyhole porosity, which is detrimental to the part quality. In this study, we developed an effective approach to locally detect the generation of keyhole pores during the printing process by leveraging machine learning and a suite of optical and acoustic sensors. Simultaneous synchrotron x-ray imaging allows the direct visualization of pore generation events inside the sample, offering high-fidelity ground truth. A neural network model adopting SqueezeNet architecture using single-sensor data was developed to evaluate the fidelity of each sensor for capturing keyhole pore generation events. Our comparative study shows that the near infrared images gave the highest prediction accuracy, followed by 100 kHz and 20 kHz microphones, and the photodiode sensitive to processing laser wavelength had the lowest accuracy. Using a single sensor, over 90% prediction accuracy can be achieved with a temporal resolution as short as 0.1 ms. A data fusion scheme was also developed with features extracted using SqueezeNet neural network architecture and classification using different machine learning algorithms. Our work demonstrates the correlation between the characteristic optical and acoustic emissions and the keyhole oscillation behavior, and thereby provides strong physics support for the machine learning approach.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Quantum stabilization and flat hydrogen-based bands of nitrogen-doped lutetium hydride

We explore the electronic and structural properties of Lu-H-N structures with specific N,H ordering due to their remarkably narrow hydrogen-based bands at the Fermi level. Although exhibits a classical instability persisting up to 17 GPa, it is anharmonically stable near ambient pressure when accounting for quantum nuclear effects. The presence of flat bands near is understood to arise from destructive quantum interference between and surrounding orbitals, with certain types of defects leaving the flat bands unaffected. The results suggest that if this system is superconducting, there is an optimal pressure near ambient where the superconducting is maximized by anharmonically stabilized low-frequency and nonadiabatically coupled high-frequency hydrogen modes. Despite the metastability of this structure, its dynamical stability when modeled beyond a classical harmonic approach suggests the narrow bands near do not cause structural distortions in certain Lu-H-N stoichiometries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1974

A study of first month space malfunctions

The study examines the first-month space performance of 57 Goddard Space Flight Center spacecraft. It is a sequel to a previous study of first-day space malfunctions of the same 57 spacecraft. A total of 154 malfunctions, of which 88 were classified as failures, have been summarized by year of occurrence, by major subsystem of a spacecraft, by type of defect, and by severity. Of the 57 spacecraft, 45 had one or more failures during the first month in space. However, the mission criticality data show that, of the 154 malfunctions, less than 10 percent would have resulted in major loss (50-100 percent) to the mission, and due to redundancy, only 5 percent did result in major loss to the mission. The data show that more than 50 percent of the first month's failures occurred in the first operational day in space. The data also show that, for the first month in space, the ratio of system-test failures to space failures for various devices ranged from 3 to 1 up to 10 to 1. For six spacecraft programs, the ratios of test to space failures ranged from 2 to 1 up to 8 to 1.

Timmins, A. R.↗