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  • 1
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    Unit cell geometry of 3-D braided structures (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The traditional approach used in modeling of composites reinforced by three-dimensional (3-D) braids is to assume a simple unit cell geometry of a 3-D braided structure with known fiber volume fraction and orientation. In this article, we first examine 3-D braiding methods in the light of braid structures, followed by the development of geometric models for 3-D braids using a unit cell approach. The unit cell geometry of 3-D braids is identified and the relationship of structural parameters such as yarn orientation angle and fiber volume fraction with the key processing parameters established. The limiting geometry has been computed by establishing the point at which yarns jam against each other. Using this factor makes it possible to identify the complete range of allowable geometric arrangements for 3-D braided preforms. This identified unit cell geometry can be translated to mechanical models which relate the geometrical properties of fabric preforms to the mechanical responses of composite systems.
    Keywords: MECHANICAL ENGINEERING
    Type: Journal of Reinforced Plastics and Composites (ISSN 0731-6844); 12; 7; p. 752-768.
    Format: text
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  • 2
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    Analysis of rolling contact spall life in 440 C steel bearing rims (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The results of a two year study of the mechanisms of spall failure in the HPOTP bearings are described. The objective was to build a foundation for detailed analyses of the contact life in terms of: cyclic plasticity, contact mechanics, spall nucleation, and spall growth. Since the laboratory rolling contact testing is carried out in the 3 ball/rod contact fatigue testing machine, the analysis of the contacts and contact lives produced in this machine received attention. The results from the experimentally observed growth lives are compared with calculated predictions derived from the fracture mechanics calculations.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-CR-184101 , NAS 1.26:184101
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Development of braided rope seals for hypersonic engine applications: Flow modeling (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A new type of engine seal is being developed to meet the needs of advanced hypersonic engines. A seal braided of emerging high temperature ceramic fibers comprised of a sheath-core construction was selected for study based on its low leakage rates. Flexible, low-leakage, high temperature seals are required to seal the movable engine panels of advanced ramjet-scramjet engines either preventing potentially dangerous leakage into backside engine cavities or limiting the purge coolant flow rates through the seals. To predict the leakage through these flexible, porous seal structures new analytical flow models are required. Two such models based on the Kozeny-Carman equations are developed herein and are compared to experimental leakage measurements for simulated pressure and seal gap conditions. The models developed allow prediction of the gas leakage rate as a function of fiber diameter, fiber packing density, gas properties, and pressure drop across the seal. The first model treats the seal as a homogeneous fiber bed. The second model divides the seal into two homogeneous fiber beds identified as the core and the sheath of the seal. Flow resistances of each of the main seal elements are combined to determine the total flow resistance. Comparisons between measured leakage rates and model predictions for seal structures covering a wide range of braid architectures show good agreement. Within the experimental range, the second model provides a prediction within 6 to 13 percent of the flow for many of the cases examined. Areas where future model refinements are required are identified.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TM-105942 , E-6166-1 , NAS 1.15:105942
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    High temperature dynamic engine seal technology development (1992)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Combined cycle ramjet/scramjet engines being designed for advanced hypersonic vehicles, including the National Aerospace Plane (NASP), require innovative high temperature dynamic seals to seal the sliding interfaces of the articulated engine panels. New seals are required that will operate hot (1200 to 2000 F), seal pressures ranging from 0 to 100 psi, remain flexible to accommodate significant sidewall distortions, and resist abrasion over the engine's operational life. This report reviews the recent high temperature durability screening assessments of a new braided rope seal concept, braided of emerging high temperature materials, that shows promise of meeting many of the seal demands of hypersonic engines. The paper presents durability data for: (1) the fundamental seal building blocks, a range of candidate ceramic fiber tows; and for (2) braided rope seal subelements scrubbed under engine simulated sliding, temperature, and preload conditions. Seal material/architecture attributes and limitations are identified through the investigations performed. The paper summarizes the current seal technology development status and presents areas in which future work will be performed.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TM-105641 , E-6945 , NAS 1.15:105641 , National Aerospace Plane Mid-Term Technology Review; Apr 20, 1992 - Apr 24, 1992; Monterey, CA; United States
    Format: application/pdf
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  • 5
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    Engine panel seals for hypersonic engine applications: High temperature leakage assessments and flow modelling (1992)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A critical mechanical system in advanced hypersonic engines is the panel-edge seal system that seals gaps between the articulating horizontal engine panels and the adjacent engine splitter walls. Significant advancements in seal technology are required to meet the extreme demands placed on the seals, including the simultaneous requirements of low leakage, conformable, high temperature, high pressure, sliding operation. In this investigation, the seal concept design and development of two new seal classes that show promise of meeting these demands will be presented. These seals include the ceramic wafer seal and the braided ceramic rope seal. Presented are key elements of leakage flow models for each of these seal types. Flow models such as these help designers to predict performance-robbing parasitic losses past the seals, and estimate purge coolant flow rates. Comparisons are made between measured and predicted leakage rates over a wide range of engine simulated temperatures and pressures, showing good agreement.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TM-105260 , E-6545 , NAS 1.15:105260 , International Symposium on Transport Phenomena and Dynamics of Rotating Machinery; Apr 05, 1992 - Apr 08, 1992; Honolulu, HI; United States
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  • 6
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    Development of braided rope seals for hypersonic engine applications - Flow modeling (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Keywords: MECHANICAL ENGINEERING
    Type: Journal of Propulsion and Power (ISSN 0748-4658); 9; 3; p. 456-461.
    Format: text
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