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  • 1
    facet.materialart.
    Unbekannt
    In:  Other Sources
    Publikationsdatum: 2019-01-25
    Beschreibung: Transient vibration test criteria, developed for spacecraft hardware, provide a test rationale to verify the capability of the hardware to withstand the low and mid frequency transient vibration environments induced by launch vehicle events. A test method, consisting of a series of discrete frequency, limited cycle, modulated sine wave pulses, was developed to avoid the slow swept sine drawbacks, yet provide a repeatable test that would excite all frequencies. The shape of the waveform is that of the classic response of the mass of a one degree of freedom system when it is base-excited by an exponentially decayed sine wave transient. Criteria were developed to define pulse amplitudes, shapes, and center frequencies from spacecraft loads analyses. Test tolerance criteria were also developed and specified. The transient vibration test criteria were implemented on spacecraft flight hardware and provided a more realistic test simulation (i.e., less conservative) for qualification of spacecraft hardware without risk of undertest.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Shock and Vibration Information Center The Shock and Vibration Bull. 54, Pt. 3; p 99-110
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2019-07-13
    Beschreibung: The behavior of long tethers (10-100 km) in space are addressed under two failure situations with potential safety impact: instantaneous jamming of the reel controlling the tether during deployment and cutting of the tether due to a meteor strike or other similar phenomena. Dual and multiple mass point models were used in the SAO SKYHOOK program to determine this behavior. The results of the program runs were verified analytically or by comparison with previously verified results. The study included the effects of tether damping and air drag where appropriate. Most runs were done with the tether system undamped since we believe this best represents the true behavior of the tether. Means for controlling undesirable behavior of the tether, such as viscous dampers in the subsatellite, were also studied.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-162034 , NAS 1.26:162034
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Publikationsdatum: 2019-07-13
    Beschreibung: The width-tapered double-cantilever-beam (WTDCB) specimen configuration used to determine the Mode-I interlaminar fracture energy (IFE) of composites has special advantages for routine development work and for quality-assurance purposes. These advantages come primarily from the simplicity of testing and the fact that the specimen is designed for constant change in compliance with crack length, so that the computation of Mode-I IFE is independent of crack length. In this paper, a simplified technique for fabrication and testing WTDCB specimens is described. Also presented are the effects of fiber orientation and specimen dimensions, a comparison of data obtained using the WTDCB specimens and other specimen geometries, and comparison of data obtained at different laboratories. It is concluded that the WTDCB gives interlaminar Mode-I IFE essentially equal to other type specimens, and that it can be used for rapid screening in resin-development work and for quality assurance of composite materials.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Technology vectors; Apr 03, 1984 - Apr 05, 1984; Reno, NV
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Publikationsdatum: 2019-07-13
    Beschreibung: Finite element models were used to study the effects of notch angle variations on the stress state within an Iosipescu shear test speciment. These analytical results were also studied to determine the feasibility of using strain gage rosettes and a modified extensometer to measure shear strains in this test specimen. Analytical results indicate that notch angle variations produced only small differences in simulated shear properties. Both strain gage rosettes and the modified extensometer were shown to be feasible shear strain transducers for the test method. The Iosipoescu shear test fixture was redesigned to incorporate several improvements. These improvements include accommodation of a 50 percent larger specimen for easier measurement of shear train, a clamping mechanism to relax strict tolerances on specimen width, and a self contained alignment tool for use during specimen installation. A set of in-plane and interlaminar shear properties were measured for three graphite fabric/epoxy composites of T300/934 composite material. The three weave patterns were Oxford, 5-harness satin, and 8-harness satin.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA-CR-174346 , NAS 1.26:174346 , UWME-DR-401-103-1
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    facet.materialart.
    Unbekannt
    In:  CASI
    Publikationsdatum: 2005-03-28
    Beschreibung: In many structures the final stress states are dependent on the sequence of construction or the stress states at various stages of construction are of interest. Such problems can be analyzed using finite element programs that have the capability of adding (birthing) elements to simulate the progress of construction. However, the usual procedure of assembling elements may lead to numerical instabilities or stress states that are unrealistic. Both problems are demonstrated in the analysis of a structure using the program ADINA. A technique which combines application of a preload with element birthing to overcome these problems is described and illustrated.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Langley Research Center Res. in Struct. and Dyn., 1984; p 395-404
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Publikationsdatum: 2005-03-28
    Beschreibung: A technique utilizing finite element analysis, liquid impact kinematics, and momentum theory is described and compared to single-drop impact test data performed on various configurations of coated ceramic material. The method correlates well with test data and is useful in predicting the single-drop impact damage velocity threshold for low-density, coated ceramic materials.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Langley Research Center Res. in Struct. and Dyn., 1984; p 385-393
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    facet.materialart.
    Unbekannt
    In:  CASI
    Publikationsdatum: 2005-03-28
    Beschreibung: An algorithm is outlined for simulating the contact surface erosion for impact problems. The algorithm dynamically relocates the contact surface as projectile and target materials exceed their failure criterion. Example computations of axisymmetric and oblique impacts are compared with experimental data.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Langley Research Center Res. in Struct. and Dyn., 1984; p 315-324
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Publikationsdatum: 2005-03-28
    Beschreibung: The evaluation of the total probability of a plastic collapse failure P sub f for a highly redundant structure of random interdependent plastic moments acted on by random interdepedent loads is a difficult and computationally very costly process. The evaluation of reasonable bounds to this probability requires the use of second moment algebra which involves man statistical parameters. A computer program which selects the best strategy for minimizing the interval between upper and lower bounds of P sub f is now in its final stage of development. The relative importance of various uncertainties involved in the computational process on the resulting bounds of P sub f, sensitivity is analyzed. Response sensitivities for both mode and system reliability of an ideal plastic portal frame are shown.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Langley Research Center Res. in Struct. and Dyn., 1984; p 159-179
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    facet.materialart.
    Unbekannt
    In:  CASI
    Publikationsdatum: 2005-03-28
    Beschreibung: Research aimed at faster, more cost effective parallel machines and algorithms for improving designer productivity with finite element computations is discussed. A set of 8 boards, containing 4 nearest neighbor connected arrays of commercially available floating point chips and substantial memory, are inserted into a commercially available machine. One-tenth Mflop (64 bit operation) processors provide an 89% efficiency when solving the equations arising in a finite element problem for a single variable regular grid of size 40 by 40 by 40. This is approximately 15 to 20 times faster than a much more expensive machine such as a VAX 11/780 used in double precision. The efficiency falls off as faster or more processors are envisaged because communication times become dominant. A novel successive overrelaxation algorithm which uses cyclic reduction in order to permit data transfer and computation to overlap in time is proposed.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: NASA. Langley Research Center Res. in Struct. and Dyn., 1984; p 15-29
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Publikationsdatum: 2006-02-14
    Beschreibung: Solid rocket booster cavity collapse flight measurements included external pressures on the motor case and aft skirt, internal motor case pressures, accelerometers located in the forward skirt, mid-body area, and aft skirt, as well as strain gages located on the skin of the motor case. This flight data yielded applied pressure longitudinal and circumferential distributions which compare well with model test predictions. The internal motor case ullage pressure, which is below atmospheric due to the rapid cooling of the hot internal gas, was more severe (lower) than anticipated due to the ullage gas being hotter than predicted. The structural dynamic response characteristics were as expected. Structural ring and wall damage are detailed and are considered to be attributable to the direct application of cavity collapse pressure combined with the structurally destabilizing, low internal motor case pressure.
    Schlagwort(e): STRUCTURAL MECHANICS
    Materialart: Shock and Vibration Inform. Center The Shock and Vibration Bull., No. 52. Part 2; p 21-26
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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