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  • 1
    Publication Date: 2019-01-25
    Description: 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.
    Keywords: STRUCTURAL MECHANICS
    Type: Shock and Vibration Information Center The Shock and Vibration Bull. 54, Pt. 3; p 99-110
    Format: text
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  • 2
    Publication Date: 2019-06-27
    Description: Nonlinear expressions are developed to relate the orientation of the deformed beam cross section, torsion, local components of bending curvature, angular velocity, and virtual rotation to deformation variables. The deformed beam kinematic quantities are proven to be equivalent to those derived from various rotation sequences by identifying appropriate changes of variable based on fundamental uniqueness properties of the deformed beam geometry. The torsion variable used is shown to be mathematically analogous to an axial deflection variable commonly used in the literature. Rigorous applicability of Hamilton's principle to systems described by a class of quasi-coordinates that includes these variables is formally established.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-1566 , A-7985 , AVRADCOM-TR-80-A-1
    Format: application/pdf
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  • 3
    Publication Date: 2019-06-28
    Description: Techniques to predict the dynamic response and the structural dynamic loads of flat plate photovoltaic arrays due to wind turbulence were analyzed. Guidelines for use in predicting the turbulent portion of the wind loading on future similar arrays are presented. The dynamic response and the loads dynamic magnification factor of the two array configurations are similar. The magnification factors at a mid chord and outer chord location on the array illustrated and at four points on the chord are shown. The wind tunnel test experimental rms pressure coefficient on which magnification factors are based is shown. It is found that the largest response and dynamic magnification factor occur at a mid chord location on an array and near the trailing edge. A technique employing these magnification factors and the wind tunnel test rms fluctuating pressure coefficients to calculate design pressure loads due to wind turbulence is presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-164745 , DOE/JPL-954833-81/4 , JPL-9950-594
    Format: application/pdf
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  • 4
    Publication Date: 2019-06-28
    Description: The results of an experimental analysis (boundary layer wind tunnel test) of the aerodynamic forces resulting from winds acting on flat plate photovoltaic arrays are presented. Local pressure coefficient distributions and normal force coefficients on the arrays are shown and compared to theoretical results. Parameters that were varied when determining the aerodynamic forces included tilt angle, array separation, ground clearance, protective wind barriers, and the effect of the wind velocity profile. Recommended design wind forces and pressures are presented, which envelop the test results for winds perpendicular to the array's longitudinal axis. This wind direction produces the maximum wind loads on the arrays except at the array edge where oblique winds produce larger edge pressure loads. The arrays located at the outer boundary of an array field have a protective influence on the interior arrays of the field. A significant decrease of the array wind loads were recorded in the wind tunnel test on array panels located behind a fence and/or interior to the array field compared to the arrays on the boundary and unprotected from the wind. The magnitude of this decrease was the same whether caused by a fence or upwind arrays.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-164454 , DOE/JPL-954833-81/3
    Format: application/pdf
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  • 5
    Publication Date: 2019-07-13
    Description: 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.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-162034 , NAS 1.26:162034
    Format: application/pdf
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  • 6
    Publication Date: 2019-06-28
    Description: A new formulation of finite element method is accomplished by the Hellinger-Reissner principle for which the stress equilibrium conditions are not introduced initially but are brought-in through the use of additional internal displacement parameters. The method can lead to the same result as the assumed stress hybrid model. However, it is more general and more flexible. The use of natural coordinates for stress assumptions leads to elements which are less sensitive to the choice of reference coordinates. Numerical solutions by 3-D solid element indicate that more efficient elements can be constructed by assumed stresses which only partially satisfy the equilibrium conditions.
    Keywords: STRUCTURAL MECHANICS
    Format: text
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  • 7
    Publication Date: 2019-07-13
    Description: 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.
    Keywords: STRUCTURAL MECHANICS
    Type: Technology vectors; Apr 03, 1984 - Apr 05, 1984; Reno, NV
    Format: text
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  • 8
    Publication Date: 2019-07-13
    Description: An accelerated characterization procedure has been developed for time-dependent compliances and strengths of resin-matrix composites. The procedure, which is based on a time-temperature-stress superposition principle, is applied to a graphite/epoxy laminate T300/934. Creep rupture analytical models are discussed, and model predictions are compared with experimental data. Master curves for the creep compliances are given.
    Keywords: STRUCTURAL MECHANICS
    Type: Composite structures; Sep 16, 1981 - Sep 18, 1981; Paisley
    Format: text
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  • 9
    Publication Date: 2019-07-13
    Description: 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.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-174346 , NAS 1.26:174346 , UWME-DR-401-103-1
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  • 10
    Publication Date: 2005-03-28
    Description: 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.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Dyn., 1984; p 395-404
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