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  • Other Sources  (8)
  • 1985-1989  (8)
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  • 1
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    Unknown
    Space Shuttle Main Engine fuel preburner augmented spark igniter shutdown detonations (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Detonations were experienced in the Space Shuttle Main Engine fuel preburner (FPB) augmented spark igniter (ASI) during engine cutoff. Several of these resulted in over pressures sufficient to damage the FPB ASI oxidizer system. The detonations initiated in the FPB ASI oxidizer line when residual oxidizer (oxygen) in the line mixed with backflowing fuel (hydrogen) and detonated. This paper reviews the damage history to the FPB ASI oxidizer system, an engineering assessment of the problem cause, a verification of the mechanisms, the hazards associated with the detonations, and the solution implemented.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: AIAA PAPER 86-1445
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Long-term environmental effects and flight service evaluation of composite materials (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Results of a NASA-Langley sponsored research program to establish the long term effects of realistic flight environments and ground based exposure on advanced composite materials are presented. The effects of moisture, ultraviolet radiation, aircraft fuels and fluids, sustained stress, and fatigue loading are reported. Residual strength and stiffness as a function of exposure time and exposure location are reported for seven different material systems after 10 years of worldwide outdoor exposure. Flight service results of over 300 composite components installed on rotorcraft and transport aircraft are included. Over 4 million total component flight hours were accumulated on various aircraft since initiation of flight service in 1973. Service performance, maintenance characteristics, and residual strength of numerous composite components installed on commercial and military aircraft are reported as a function of flight hours and years in service. Residual strength test results of graphite/epoxy spoilers with 10 years of worldwide service and over 28,000 flight hours are reported.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-TM-89067 , NAS 1.15:89067
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Unknown
    Impact resistance and interlaminar fracture toughness of through-the-thickness reinforced graphite/epoxy (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Five through-the-thickness stitch configurations are analyzed to determine the effect of impact resistance and interlaminar fracture toughness on T3000/3501-6 graphite/epoxy. The test specimens were stitched with either polyester or Kevlar yarns and with various stitch parameters. Tension and compression mechanical, impact and compression-after-impact, and double cantilever beam tests were conducted. It is observed that the stitched laminates have tension and compression strengths 20-25 percent lower than the strengths of unstitched laminates, the tension strength of stitched laminates is reduced with increasing number of stitches, and the compression strength increases as the number of stitches are increased. The impact data reveal that the Kevlar stitched laminates have less damage than unstitched laminates; the most effective configuration for suppressing impact damage and improving interlaminar fracture toughness consists of Kevlar yarns 1/4 inch apart with eight stitches per inch. The mode 1 critical strain energy release rate for the 1/4 inch Kevlar eight stitch laminate was calculated as 30 times higher than that of the unstitched.
    Keywords: COMPOSITE MATERIALS
    Type: AIAA PAPER 86-1020
    Format: text
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  • 4
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    Unknown
    Measurement and analysis of critical crack tip processes during fatigue crack growth (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The mechanics of fatigue crack growth under constant-amplitudes and variable-amplitude loading were examined. Critical loading histories involving relatively simple overload and overload/underload cycles were studied to provide a basic understanding of the underlying physical processes controlling crack growth. The material used for this study was 7091-T7E69, a powder metallurgy aluminum alloy. Local crack-tip parameters were measured at various times before, during, and after the overloads, these include crack-tip opening loads and displacements, and crack-tip strain fields. The latter were useed, in combination with the materials cyclic and monotonic stress-strain properties, to compute crack-tip residual stresses. The experimental results are also compared with analytical predictions obtained using the FAST-2 computer code. The sensitivity of the analytical model to constant-amplitude fatigue crack growth rate properties and to through-thickness constrain are studied.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-172597 , NAS 1.26:172597
    Format: application/pdf
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  • 5
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    Unknown
    Chemical kinetic performance losses for a hydrogen laser thermal thruster (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Projected requirements for efficient, economical, orbit-raising propulsion systems have generated investigations into several potentially high specific impulse, moderate thrust, advanced systems. One of these systems, laser thermal propulsion, utilizes a high temperature plasma as the enthalpy source. The plasma is sustained by a focused laser beam which maintains the plasma temperature at levels near 20,000 K. Since such temperature levels lead to total dissociation and high ionization, the plasma thruster system potentially has a high specific impulse decrement due to recombination losses. The nozzle flow is expected to be sufficiently nonequilibrium to warrant concern over the achievable specific impluse. This investigation was an attempt at evaluation of those losses. The One-Dimensional Kinetics (ODK) option of the Two-Dimensional Kinetics (TDK) Computer Program was used with a chemical kinetics rate set obtained from available literature to determine the chemical kinetic energy losses for typical plasma thruster conditions. The rates were varied about the nominal accepted values to band the possible losses. Kinetic losses were shown to be highly significant for a laser thermal thruster using hydrogen. A 30 percent reduction in specific impulse is possible simply due to the inability to completely extract the molecular recombination energy.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: AIAA PAPER 85-0907
    Format: text
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  • 6
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    Fatigue crack growth with single overload - Measurement and modeling (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: This paper compares experiments with an analytical model of fatigue crack growth under variable amplitude. The stereoimaging technique was used to measure displacements near the tips of fatigue cracks undergoing simple variations in load amplitude-single overloads and overload/underload combinations. Measured displacements were used to compute strains, and stresses were determined from the strains. Local values of crack driving force (Delta-K effective) were determined using both locally measured opening loads and crack tip opening displacements. Experimental results were compared with simulations made for the same load variation conditions using Newman's FAST-2 model. Residual stresses caused by overloads, crack opening loads, and growth retardation periods were compared.
    Keywords: STRUCTURAL MECHANICS
    Type: Effects of load and thermal histories on mechanical behavior of materials; Feb. 25, 26, 1987; Denver, CO; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Advances in Composites Technology (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A significant level of research is currently focused on the development of tough resins and high strain fibers in an effort to gain improved damage tolerance. Moderate success has been achieved with the development of new resins such as PEEK and additional improvements look promising with new thermoplastic resins. Development of innovative material forms such as 2-D and 3-D woven fabrics and braided structural subelements is also expected to improve damage tolerance and durability of composite hardware. The new thrust in composites is to develop low cost manufacturing and design concepts to lower the cost of composite hardware. Processes being examined include automated material placement, filament winding, pultrusion, and thermoforming. The factory of the future will likely incorporate extensive automation in all aspects of manufacturing composite components.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-TM-86353 , NAS 1.15:86353
    Format: application/pdf
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  • 8
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    Modelling and measurement of crack closure and crack growth following overloads and underloads (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Ignoring crack growth retardation following overloads can result in overly conservative life predictions in structures subjected to variable amplitude fatigue loading. Crack closure is believed to contribute to the crack growth retardation, although the specific closure mechanism is dabatable. The delay period and corresponding crack growth rate transients following overload and overload/underload cycles were systematically measured as a function of load ratio and overload magnitude. These responses are correlated in terms of the local 'driving force' for crack growth, i.e. the effective stress intensity factor range. Experimental results are compared with the predictions of a Dugdale-type (1960) crack closure model, and improvements in the model are suggested.
    Keywords: STRUCTURAL MECHANICS
    Type: Engineering Fracture Mechanics (ISSN 0013-7944); 33; 6 19
    Format: text
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