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At least 1,117 records · Page 62

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NASA NTRS1986

Deformation and damage of composite plates under impact loading

Transient deformation and damage were studied in impacted graphite/epoxy plates. The plates were 8-ply and 16-ply quasi-isotropic laminates clamped around a 12.7 cm diameter circumference. They were instrumented with surface and embedded strain gages and loaded by a 202 gr mass dropped from a height of 1.8 m. The load history and imparted energy were obtained by means of an accelerometer attached to the impactor. Transient strains at various locations through the thickness and at various distances from the loading point were obtained. The characteristic features of the strain records are associated with specific failure modes in the laminate. The deformation history was also correlated with the induced damage as detected by X-radiography and ultrasonics. Impact damage is more extensive in the thicker laminate. Damage takes the form of delaminated strips parallel to the fiber direction in each ply and increasing in length from top to bottom.

Daniel, I. M.↗

NASA NTRS1987

Quick-Change Anode for Plating

Proposed fastener for attaching electroplating anode improves quality of plating and increases productivity. Notches in twist-lock fastener mates with projections on end of anode bar. Fastener made of titanium for compatibility with copper-plating solution. Also constructed in snap-on, snap-off configuration.

Beasley, J. L.↗

NASA NTRS1987

Buckling Analysis of Rectangular Plates With Holes

BUCKO is computer program developed to predict buckling of rectangular compression-loaded orthotropic plate with centrally located cutout. Plate assumed balanced, symmetric laminate of uniform thickness. Cutout shape elliptical, circular, rectangular, or square. Package includes sample data demonstrating essence of program and ease of use. Written in FORTRAN V.

Nemeth, M. P.↗

NASA NTRS1986

Qualification Testing of General Electric 50 Ah Nickel-Cadmium Cells with New Separator and New Positive Plate Processing

Forty-two 50 Ah aerospace nickel-cadmium cells were delivered to Goddard Space Flight Center (GSFC) by General Electric (GE) in February, 1985, for the purpose of evaluating and qualifying a new nylon separator material Pellon 2536, and the new GE Positive Plate Nickel Attack Control Passivation process. Testing began in May, 1985, at the Naval Weapons Support Center (NWSC) in Crane, Indiana with standard initial evaluation tests. Life cycling in both Low Earth Orbit (LEO) and Geosynchronous Orbit (GEO) began in July, 1985, with approximately 1200 LEO cycles complete at this writting. Early test results show that cells with positive plate passivation exhibit higher than normal charge voltage characteristics. Other aspects of performance were nominal.

Morrow, G. W.↗

NASA NTRS1986

Modes of vibration on sqaure fiberglass epoxy composite thick plate

The frequencies and nodal patterns of a square thick plate of unidirectional fiberglass epoxy composite are measured experimentally. The constituent material is transversely isotropic. The plate is transversely excited at the center of the upper face, its resonant frequencies in the frequency range of 3 kHz to 21.73 kHz are detected and the measured nodal patterns are sketched.

Williams, J. H., Jr.↗

NASA NTRS1986

Triangular element for analysis of a stretched plate weakened by a part-through hole

A C0-type triangular element formulation in orthogonal curvilinear coordinates has been developed, based on assumptions of transverse inextensibility and layerwise constant shear angle, for analysis of a stretched homogeneous plate weakened by a part-through hole. The element stiffness matrix and consistent load vector have been derived using an assumed-quadratic-displacement (in the curvilinear coordinate plane) potential-energy approach. Numerical results obtained using the straight-sided triangular element version indicate the presence of transverse shear deformation in a stretched homogeneous plate weakened by a symmetrically located concentric hole.

Chaudhuri, R. A.↗

NASA NTRS1985

Buckling of simply supported plate assemblies subject to shear loading

An analysis is presented of the shear buckling load of an arbitrary simply-supported prismatic plate assembly or stiffened panel configuration. The method utilizes stiffness matrices developed by Wittrick (1968). For the restraint of simple support along edges perpendicular to the longitudinal direction, various wavelengths of response are combined using an energy method that involves only a boundary integral. Numerical results for plate and panel configurations show the accuracy and convergence of the method.

Anderson, M. S.↗

NASA NTRS1986

The Shane-Wirtanen counts - Plate correction factors and correlation functions

It has recently been argued that the break in the galaxy correlation function observed in the Lick counts of Shane and Wirtanen may be an artifact of plate variations in limiting magnitude. This has stimulated us to generalize our analysis of the effect of errors in the plate depths to include a possible systematic term, and to develop tests for the random and systematic errors. The tests show that neither can have appreciably affected the distinctive feature found in the galaxy two-point correlation function for the Lick sample.

Groth, Edward J.↗

NASA NTRS1987

Use of gamma ray radiation to parallel the plates of a Fabry-Perot interferometer

The use of gamma radiation to parallel the plates of a Fabry-Perot etalon is examined. The method for determining the etalon parallelism, and the procedure for irradiating the posts are described. Changes in effective gap for the etalon over the surface are utilized to measure the parallelism of the Fabry-Perot etalon. An example in which this technique is applied to an etalon of fused silica plates, which are 132 mm in diameter and coded with zinc sulfide and cryolite, with Zerodur spaces 2 cm in length. The effect of the irradiation of the posts on the thermal performance of the etalon is investigated.

Skinner, Wilbert R.↗

NASA NTRS1986

Contemporary plate motions from Lageos - A decade later

Progress made due to Lageos tracking and the participation of over 20 countries in the acquisition and analysis of precise range measurements is reviewed. Results of both the observed global and regional plate kinematics are presented. Mission accomplishments include the following: (1) laser technology advancements of more than an order of magnitude in single point range precision over the last ten years, (2) station positioning at the few centimeter accuracy level for annual solutions, and (3) the emergence of a global picture of plate kinematics.

Christodoulidis, D. C.↗

NASA NTRS1987

Wave propagation in a plate after impact by a projectile

The wave propagation in a circular plate after impact by a cylindrical projectile is studied. In the vicinity of impact, the pressure is computed numerically. An intense pressure pulse is generated that peaks 0.2 microns after impact, then drops sharply to a plateau. The response of the plate is determined adopting a modal solution of Mindlin's equations. Velocity and acceleration histories display both propagating and dispersive features.

El-Raheb, M.↗

NASA NTRS1987

Dynamic response of laminated composite plates using a three-dimensional hybrid-stress finite-element formulation

A method of analysis of dynamic response of laminated composite plates is presented. The analysis is carried by using a hybrid-stress finite element numerical technique. By using this approach, the response of simply supported laminated plates subjected to sinusoidal loading are investigated. For the solution of the finite element equations of motion of free vibrations and dynamic response problems, two effective methods of solution, the space iteration method and the Newmark direct integration method are used. These two methods are discussed here.

Liou, W. J.↗

NASA NTRS1988

Intraplate deformation, stress in the lithosphere and the driving mechanism for plate motions

During this period work was carried out on three fronts relevant to the understanding of intraplate deformation, stress in the lithosphere, and the driving mechanisms for plate motions: (1) observational constraints, using GPS geodesy on the deformation in the region of the boundry between the Pacific and North American plates in central and southern California; (2) numerical modeling of the effects of temperature dependent lithospheric viscosity on the stress and strain history of extensional regimes; and (3) improvement of estimates of mantle viscosity variation, the long-wave-length density variations in the mantle, and the topography of the core-mantel boundary from modeling of geoid anomalies, nutation, and changes in length of day. These projects are described in more detail, followed by a discussion of meetings attended and a list of abstracts and papers submitted and/or published.

Hager, Bradford H.↗

NASA NTRS1986

A dual plate thermoplastic recording device for holographic interferometry

The development of a dual plate holographic interferometer using thermoplastic recording devices is described. The operational characteristics of the thermoplastic devices are investigated and optimized for fringe contrast and signal-to-noise ratio. The dual plate device was demonstrated in a transonic wind tunnel at NASA Ames Research Center. The interferograms derived from the thermoplastic device are compared with those derived from conventional photographic emulsions. The fringe contrast achieved with the optimized thermoplastic device is equivalent to the contrast achieved with conventional techniques.

Umstatter, Holly L.↗

NASA NTRS1987

Plates and their motions

Work on plate motions published in 1983-1986 and in early 1987 is reviewed. Models for these motions, including global ones for driving forces and local ones for subduction history and back-arc spreading, are addressed. The problem of reference frames, both hotspot and paleomagnetic, is discussed. The assessment of errors in plate motion studies is reviewed.

Jurdy, Donna M.↗

NASA NTRS1987

A finite element large deflection random response analysis of beams and plates subjected to acoustic loading

A finite element formulation is presented for the analysis of beams and rectangular plates undergoing large deflections subjected to Gaussian white noise excitations. Single-mode response is assumed in the present formulation. Root-mean-square (RMS) maximum deflections for simply supported and clamped beams and plates at various sound spectrum levels are obtained and compared with solutions using the Fokker-Planck-Kolmogorov equation and the equivalent linearization methods. RMS maximum stains and equivalent linear frequencies are compared with the equivalent linearization results for assessment of the accuracy of the finite element method.

Mei, Chuh↗

NASA NTRS1987

Evidence for divergent plate-boundary characteristics and crustal spreading on Venus

Detailed examination of the topography and morphology of western Aphrodite Terra reveals numerous features that are similar to terrestrial divergent plate-boundary characteristics. Individual domains between fracture-zone-like discontinuities contain a variety of bilaterally symmetrical topographic elements that suggest that topographic features have been created at rise crests, rifted and separated, and moved laterally to their present symmetrical positions. The topographic and morphologic similarities, together with strikingly similar mirror-image map patterns on both sides of the rise axis, suggest that western Aphrodite Terra shares the characteristics of oceanic divergent plate boundaries, and is the site of crustal spreading on Venus. Topographic profiles are consistent with spreading rates of the order of several centimeters per year.

Head, James W., III↗

NASA NTRS1987

Stress concentration around a part-through hole weakening a laminated plates

A quasi-three-dimensional-elasticity type theory, based on the assumptions of transverse inextensibility and layerwise constant shear-angle, is presented, in the context of an assumed quadratic displacement potential energy approach, for analyzing an edge-loaded laminated plate weakened by the presence of a part-through hole. Numerical results, obtained using the C-deg-type triangular finite element, indicate the existence of severe cross-sectional warping in the vicinity of the hole and plate boundaries. Furthermore, the three-dimensional nature of the stress concentration factor in the neighborhood of the hole boundary is clearly exhibited. Besides, very high stress concentration factors are found in the layer weakened by the part-through hole. The numerical results presented should serve as bench-mark solutions for future comparisons.

Chaudhuri, Reaz A.↗