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  • 1
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    An evaluation of the pressure proof test concept for 2024-T3 aluminium alloy sheet (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The concept of pressure proof testing of fuselage structures with fatigue cracks to insure structural integrity was evaluated from a fracture mechanics viewpoint. A generic analytical and experimental investigation was conducted on uniaxially loaded flat panels with crack configurations and stress levels typical of longitudinal lap splice joints in commercial transport aircraft fuselages. The results revealed that the remaining fatigue life after a proof cycle was longer than that without the proof cycle because of crack growth retardation due to increased crack closure. However, based on a crack length that is slightly less than the critical value at the maximum proof stress, the minimum assured life or proof test interval must be no more than 550 pressure cycles for a 1.33 proof factor and 1530 pressure cycles for a 1.5 proof factor to prevent in-flight failures.
    Keywords: STRUCTURAL MECHANICS
    Type: In: Structural integrity of aging airplanes (A93-45772 19-01); p. 115-129.
    Format: text
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  • 2
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    Impact damage and residual tension strength of a thick graphite/epoxy rocket motor case (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Impacters of various masses were dropped from various heights onto thick graphite/epoxy filament-wound cylinders. The cylinders represented filament-wound cases made for the booster motors of the Space Shuttle. Tups of various shapes were affixed to the impacters. Some of the cylinders were filled with inert propellant, and some were empty. The cylinders were impacted numerous times around the circumference and then cut into tension coupons, each containing an impact site. The size of the damage and the residual tension strength were measured. For hemispherical tups, strength was reduced as much as 30 percent by nonvisible damage. The damage consisted of matrix cracking and broken fibers. Analytical methods were used to predict the damage and residual tension strength. A factor of safety to account for nonvisible damage was determined. For corner and rod shaped tups, any damage that resulted in strength loss was readily visible.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 29; 3, Ma
    Format: text
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  • 3
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    Some factors that affect the inspection of aircraft for fatigue damage (1971)
    In:  CASI
    Details
    Publication Date: 2005-11-27
    Description: Fatigue crack length relationship with aircraft inspection intervals and structural reinforcement, high strength materials, and aircraft usage effects
    Keywords: STRUCTURAL MECHANICS
    Type: NASA AIRCRAFT SAFETY AND OPERATING PROBL., VOL. 1 1971; P 391-401
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  • 4
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    Many-body-theory study of lithium photoionization (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: A detailed theoretical calculation is carried out for the photoionization of lithium at low energies within the framework of Brueckner-Goldstone perturbational approach. In this calculation extensive use is made of the recently developed multiple-basis-set technique. Through this technique all second-order perturbation terms, plus a number of important classes of terms to infinite order, have been taken into account. Analysis of the results enables one to resolve the discrepancies between two previous works on this subject. The detailed calculation also serves as a test on the convergence of the many-body perturbation-expansion approach.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: Physical Review A - General Physics; vol. 11
    Format: text
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  • 5
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    An assessment of buffer strips for improving damage tolerance of composite laminates (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Graphite/epoxy panels with buffer strips were tested in tension to measure their residual strength with crack-like damage. Panels were made with (45/0/-45/90)2S and (45/0/-45/0)2S layups. The buffer strips were parallel to the loading direction. They were made by replacing narrow strips of the 0 deg graphite plies with strips of either 0 deg S-Glass/epoxy or Kevlar-90/epoxy on either a one-for-one or a two-for-one basis. In a third case, 0 deg graphite/epoxy was used as the buffer material and thin, perforated Mylar strips were placed between the 0 deg plies and the cross-plies to weaken the interfaces and thus to isolate the 0 deg plies. Some panels were made with buffer strips of different width and spacings. The buffer strips arrested the cracks and increased the residual strengths significantly over those of plain laminates without buffer strips. A shear-lag type stress analysis correctly predicted the effects of layup, buffer material, buffer strip width and spacing, and the number of plies of buffer material
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Composite Materials Supplement; 14; 1, 19; 1980
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  • 6
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    Rotational and vibrational transitions for Li + H2 collisions (1977)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Close coupling calculations for integral and differential cross sections have been carried out for Li + H2 collisions with an ab initio Hartree-Fock potential energy surface. Rotational, vibrational, and vib-rotational excitation cross sections are reported at 0.4336 eV, 0.7 eV, and 0.8673 eV in the center of mass system. For pure rotational excitations, which dominate the inelastic scattering, coupling with vibrational states is not very important. For vibrational transitions, the influence of large multiquantum rotational transitions is far less than that found for Li(+) + H2 collisions.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: Chemical Physics Letters; 48; June 1
    Format: text
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  • 7
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    Two- and three-photon ionization of hydrogen and lithium (1977)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: We present the detailed result of a calculation on two- and three-photon ionization of hydrogen and lithium based on a recently proposed calculational method. Our calculation has demonstrated that this method is capable of retaining the numerical advantages enjoyed by most of the existing calculational methods and, at the same time, circumventing their limitations. In particular, we have concentrated our discussion on the relative contribution from the resonant and nonresonant intermediate states.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: Physical Review A - General Physics; vol. 16
    Format: text
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  • 8
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    Impact force as a scaling parameter (1994)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: The Federal Aviation Administration (FAR PART 25) requires that a structure carry ultimate load with nonvisible impact damage and carry 70 percent of limit flight loads with discrete damage. The Air Force has similar criteria (MIL-STD-1530A). Both civilian and military structures are designed by a building block approach. First, critical areas of the structure are determined, and potential failure modes are identified. Then, a series of representative specimens are tested that will fail in those modes. The series begins with tests of simple coupons, progresses through larger and more complex subcomponents, and ends with a test on a full-scale component, hence the term 'building block.' In order to minimize testing, analytical models are needed to scale impact damage and residual strength from the simple coupons to the full-scale component. Using experiments and analysis, the present paper illustrates that impact damage can be better understood and scaled using impact force than just kinetic energy. The plate parameters considered are size and thickness, boundary conditions, and material, and the impact parameters are mass, shape, and velocity.
    Keywords: STRUCTURAL MECHANICS
    Type: Workshop on Scaling Effects in Composite Materials and Structures; p 305-338
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  • 9
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    Overview of mechanics of materials branch activities in the computational structures area (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Base programs and system programs are discussed. The base programs include fundamental research of composites and metals for airframes leading to characterization of advanced materials, models of behavior, and methods for predicting damage tolerance. Results from the base programs support the systems programs, which change as NASA's missions change. The National Aerospace Plane (NASP), Advanced Composites Technology (ACT), Airframe Structural Integrity Program (Aging Aircraft), and High Speed Research (HSR) programs are currently being supported. Airframe durability is one of the key issues in each of these system programs. The base program has four major thrusts, which will be reviewed subsequently. Additionally, several technical highlights will be reviewed for each thrust.
    Keywords: STRUCTURAL MECHANICS
    Type: Computational Structures Technology for Airframes and Propulsion Systems; p 121-136
    Format: text
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  • 10
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    Open hole and post-impact compression fatigue of stitched and unstitched carbon/epoxy composites (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The performance is studied of a stitched uniweave fabric composite and that of a toughened tape composite. The effects of stitching on compression fatigue life are addressed. Post impact compression fatigue and open hole fatigue tests were run on an AS4/3501-6 uniweave with stitching and a toughened IM7/8551-7 tape without stitching. Stitching was found to increase the thickness and consequently the weight of the composite material. The two materials were compared on an equal carbon content basis as well as on an equal weight basis. The excess thickness in the stitched uniweave composite was responsible for the lower fatigue life, on an equal carbon basis, compared to the toughened resin tape composite. Comparison of fatigue lives on an equal carbon content basis indicated that puncture or crimp type damage from stitching has very little effect on compression failure. Post impact fatigue test showed that although the damage area in the stitched uniweave composite was twice that of the toughened tape composite, the fatigue lives of the stitched composite were significantly longer than those of the toughened composite. Thus, it appears that the increase in thickness from stitching is much more of a penalty than crimped fibers or puncture type damage from stitching.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-102676 , NAS 1.15:102676
    Format: application/pdf
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