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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

TPSAS-NF1676L-13678-DND

An area that shows promise in enhancing structural integrity of aircraft and aerospace structures is integral stitched composite technology. The most recent generation of this technology is the Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) concept. The goal of the PRSEUS concept is to provide damage-containment capability for composite structures while reducing overall structural weight. The National Aeronautics and Space Administration, the Boeing Company, and the Federal Aviation Administration (FAA) have partnered in an effort to assess the damage-containment features of a full-scale curved PRSEUS panel using the FAA Full-Scale Aircraft Structural Test Evaluation and Research facility. The background, test plan, fixture modifications, pre-test analysis, and planned experimental procedure were presented at the 2011 Aircraft Airworthiness and Sustainment Conference. This follow-on paper and presentation will provide details of the experimental procedure, test results, nondestructive inspection results, and preliminary test analysis comparison. The test program included three phases of loading and inspections: Phase I, as-built; Phase II, with barely visible impact damage (BVID); and Phase III, with a two-bay notch severing the central stiffener. Axial tension, internal pressure, and combined axial tension and internal pressure load conditions were applied during each phase using load levels that demonstrate compliance with the strength, deformation, and damage-tolerance requirements of Title 14 Code of Federal Regulations Part 25. Pressure loads were based on an operating pressure of 9.2 psi, designated as 1P, and the axial loads were based on a design limit load (DLL) of 227 kip. The Phase I test results provided a baseline. First, 50 percent limit-load levels were applied for each of the three load cases to verify proper load introduction and repeatability by examining strain and displacement results. Next, three limit-load cases were applied: limit pressure of 12.2 psi (1.33 P), axial DLL of 227 kip, and combined 1P pressure and axial DLL. Linear strain and displacement results were observed in all load cases. For Phase-II testing, the panel was impacted to introduce BVID with an energy of 40 ft-lb, with the impact located between the central stringer stitch line and flange edge. The impact created non-penetrating visual damage with fiber breaks and delamination between the skin and stringer flange. Limit-load conditions were applied followed by pressure overload of 18.4 psi (2P) and ultimate load conditions, defined as 1.5 times DLL. Inspections were performed after each load case; no damage growth was observed. For Phase-III testing, a two-bay notch was machined severing the central stiffener. The panel was then subjected to limit-load conditions, followed by combined 1P pressure while increasing axial tension load to catastrophic failure. As limit combined loads were approached, damage initiation was observed in the form of 45? splitting at 1P + 79% DLL. Axial loading was increased to 1P + 150 percent DLL causing damage to propagate to the adjacent stringer flanges. Damage was contained within the two-bay region by the stitching rows up to 1P + 176% DLL. Axial load was further increased until catastrophic failure, when a stringer rod failed at 1P + 192% DLL. These test results further verify the damage containment features of the PRSEUS concept and suggest its appropriateness for future flight vehicles.

Andrew Bergan↗
NASA NTRSDate not supplied

Simulating High Energy Dynamic Impact of IM7/PEKK Continuous Fiber Laminated Thermoplastic Composite using Open Hole Coupon Experiments

The use of advanced thermoplastic composites (TPC) for structural applications in the aerospace and automotive industries has grown increasingly popular due to their high performance, high manufactured part output, and sustainability. Enhancing verification simulations of the progressive failure in TPCs at the coupon scale is needed to better validate advanced composite material models at larger length scales, such as element level panels. MAT_213, a tabulated composite material model, has been applied to simulate high velocity dynamic impact (HEDI) and is integrated in the LS-DYNA explicit finite element (FE) software. Previous efforts using MAT_213 have calibrated HEDI simulated failures with experimental data. Traditionally simulations have relied on a structured mesh to represent quasi-isotropic panels. For this study, a continuous fiber unidirectional tape, IM7/PEKK, was analyzed through a series of verification studies of notched laminate coupons, then validation analyses of quasi-isotropic panels under HEDI were compared with experimental data. Experiments using unidirectional TPC were performed to obtain tabulated stress vs strain curves using Digital Image Correlation (DIC) for input into MAT_213. Next, notched coupon experiments were used as an intermediate step to calibrate the damage and failure behavior in MAT_213. Lastly, investigations into differences between HEDI simulations using a fiber aligned mesh were compared with experimental failure patterns and damage sizes. The use of experimentally generated material behavior along with selective mesh layout improved HEDI predictions with minimal material parameter calibration.

Polymer matrix composites↗
DOE OSTI2022

Damage Evolution of Double-Sided Copper Conductor on Multi-layer Flexible Substrate Under Bending

Abstract—Thin-film conductors continue to play an important role in flexible electronics, and thus, the performance and reliability of such conductors under mechanical loading such as stretch, bend, and twist need to be studied through experiments as well as simulations. This paper focuses on the damage evolution of the thin-film conductors under cyclic bending. Four types of double-sided copper conductors: straight trace without coverlay, straight trace with coverlay, notched trace without coverlay, and notched trace with coverlay on multi-layer substrates were studied in this work. The adaptive curvature flexure test method, which is suitable for thin-film bending, was employed in this work. Adaptive curvature flexure test is one where the flexible substrate with its conductor is positioned between two parallel plates, and the parallel plates are moved relative to each other such that the gap distance between the parallel plates changes in one of the configurations of the adaptive curvature flexure test. Different strain levels can be achieved easily in such an adaptive curvature flexure test by controlling the gap distance between the parallel plates. By subjecting flexible substrates with thin conductors to such bend tests, the fatigue life of the specimen was determined for different magnitudes of strain ranges. The results were then compared among the four types of conductors. Specimens were designed such that the conductors were placed on both sides of the substrate so that the one of the conductors would undergo tensile straining, while the other one would undergo compressive straining. It was shown that the fatigue life was highly dependent on the magnitude of strain range, and that the conductor on the compressive side failed sooner than that on the tensile side. The failed specimens were examined in a microscope at different number of cycles. Also, the resistance of the conductors, which is directly related to the reliability of thin-film conductors, was monitored in-situ during bending. The resistance change with the strain range change as well as the resistance progression with the number of cycles in tensile as well as compressive mode were determined, and such information is then used to create failure prediction models for thin-film conductors on flexible substrates.

damage evolution, flexible conductor, multi-layer ↗
DOE OSTI2022

Electromagnetic propulsion system

An electromagnetic propulsion system comprises a plurality of stator coils wound about a first axis, a plurality of support structures, a coupler that surrounds a portion of the stator coils, and a plurality of rotor coils wound about an axis that is parallel to the first axis. The stator coils are configured to receive electric current to induce a first magnetic field. The support structures support the stator coils. The coupler includes a notch oriented so that one of the support structures can pass through the notch when the coupler moves along the stator coils. The rotor coils are attached to the coupler and are configured to receive electric current to induce a magnetic field that interacts with the first magnetic field so that a magnetic force is applied to the rotor coils, thereby propelling the coupler and the rotor coils along the stator coils.

Hartman, Seth↗
DOE OSTI2025

KIPM Detector Characterization in QUIET

Kinetic Inductance Phonon‑Mediated (KIPM) detectors are superconducting microwave resonators that sense energy depositions in the substrate through a transient shift in their resonant frequency. In this work, I installed new devices in the QUIET cryogenic facility and used a network analyzer to drive them across a range of power levels. At each setting, I measured the transmitted signal and fit it to a simple notch‑filter model, allowing us to extract key performance metrics. Despite the increased noise at low power, the model consistently captured the resonance behavior. I first measured the resonance parameters as a function of RF drive power, then repeated the measurement across a range of temperatures to test whether the device behaved like an MKID. While the notch-filter fits captured the resonance reliably, the observed temperature dependence did not match the expected MKID signature — indicating that these first in-house fabricated chips are not yet functioning as true MKIDs. Overall, this reframes our work as a study of resonance parameter extraction and identification, pointing towards future iterations of device design and fabrication to get the true MKID response.

Savitala, Akash [U. Washington, Seattle (main); Fe↗
DOE OSTI2024

Effects of hydrogen partial pressure on crack initiation and growth rate in vintage X52 steel

There is an increasing interest in ensuring compatibility of existing natural gas infrastructure with conveyance of hydrogen, especially for vintage (pre-1970s) pipeline steels. While hydrogen is known to affect the fatigue and fracture resistance of these materials, there is a lack of data on its effects on crack initiation at low hydrogen partial pressure. To address this gap, the current work presents a series of fatigue tests on vintage API Grade X52 steel in pure nitrogen, air and gaseous hydrogen at partial pressures of 1 and 207 bar. Circumferential notch tension (CNT) specimens with direct current potential difference (DCPD) measurements are used to get S–N curves for crack initiation and failure, and compact tension (CT) tests to assess crack growth rates. Results indicate that air accelerates crack initiation, low hydrogen partial pressure affects the crack growth rate, and higher pressures have the largest impact on both. Surprisingly, crack initiation is faster in air than at 1 bar hydrogen partial pressure. The CNT tests also reveal that the orientation of the banded microstructure has no effect on the crack initiation site, but it influences its growth behavior. Moreover, fractography shows that hydrogen also promotes instances of quasi-cleavage and intergranular fracture, linked to embrittlement of the material. Here, these results demonstrate that, while hydrogen may impact the entirety of the fatigue process, its effects on the early stages of damage accumulation become relevant only at larger pressures. More comprehensive studies of crack initiation in hydrogen atmospheres will be critical to future codes and standards for hydrogen infrastructure.

Circumferential notch tension↗
DOE OSTI2025

Fracture toughness measurement of ceramics with fuel pellet geometry

The crack initiation of nuclear fuel pellets, driven by extreme temperature gradients, is a critical factor impacting reactor performance. Although this fact is widely acknowledged, there is limited fracture toughness data for specimens with representative geometry and fabricated using relevant processing methods. Here, to address this, a new chevron-notched short-rod specimen configuration with diameter and length both equal to 10 mm, representative of a conventional fuel pellet and tested in tension, was developed in an attempt to validly measure Mode I fracture toughness, K Ic . Test calibration was carried out by testing polycrystalline ZrO 2 , SiC, and Si 3 N 4 ceramics fabricated with conventional fuel pellet geometry and known fracture toughnesses. The results suggest that the method described in this paper produces valid K Ic measurements using conventional ceramic fuel pellets.

Ceramics↗