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At least 739 records · Page 41

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NASA NTRS1992

Transverse flexural tests as a tool for assessing damage to PMR-15 composites from isothermal aging in air at elevated temperatures

To date, the effect of thermo-oxidative aging on unidirectional composite mechanical properties has been monitored by the measurement of interlaminar shear strength (ILSS) and either three or four point longitudinal flexural strength (LFS) of the composites being tested. Both results are affected by the fiber-to-matrix bonding, the former being dependent on the shear resistance of the interface and the latter on the degree of load sharing by the fibers through the fiber/matrix interface. Recently, fiber/matrix interfacial bond strengths have been monitored using a transverse flexural strength (TFS) test method. This test method was used to evaluate the effect of fiber surface treatment on the fiber/matrix bond. The interface bonding was varied in these tests using Hercules A-fibers with three-types of surfaces that produce bonds of poor, better, and good quality. The TFS was found not only to be sensitive to the bonding, but also to the aging time of unidirectional A-fiber/PMR-15 composites. This relationship reflects the mechanism by which the PMR-15 degrades during thermal aging.

Bowles, Kenneth J.↗

NASA NTRS1993

Inclusion of transverse shear deformation in the exact buckling and vibration analysis of composite plate assemblies

The problem considered is the development of the necessary plate stiffnesses for use in the general purpose program VICONOPT for buckling and vibration of composite plate assemblies. The required stiffnesses include the effects of transverse shear deformation and are for sinusoidal response along the plate length as required in VICONOPT. The method is based on the exact solution of the plate differential equations for a composite laminate having fully populated A, B, and D stiffness matrices which leads to an ordinary differential equation of tenth order.

Anderson, Melvin S.↗

NASA NTRS1993

Influence of transverse-shear and large-deformation effects on the low-speed impact response of laminated composite plates

An analytical procedure is presented for determining the transient response of simply supported, rectangular laminated composite plates subjected to impact loads from airgun-propelled or dropped-weight impactors. A first-order shear-deformation theory is included in the analysis to represent properly any local short-wave-length transient bending response. The impact force is modeled as a locally distributed load with a cosine-cosine distribution. A double Fourier series expansion and the Timoshenko small-increment method are used to determine the contact force, out-of-plane deflections, and in-plane strains and stresses at any plate location due to an impact force at any plate location. The results of experimental and analytical studies are compared for quasi-isotropic laminates. The results indicate that using the appropriate local force distribution for the locally loaded area and including transverse-shear-deformation effects in the laminated plate response analysis are important. The applicability of the present analytical procedure based on small deformation theory is investigated by comparing analytical and experimental results for combinations of quasi-isotropic laminate thicknesses and impact energy levels. The results of this study indicate that large-deformation effects influence the response of both 24- and 32-ply laminated plates, and that a geometrically nonlinear analysis is required for predicting the response accurately.

Ambur, Damodar R.↗

NASA NTRS1992

Transverse ion acceleration by localized lower hybrid waves in the topside auroral ionosphere

Up to now, observations had been unable to show conclusively a one-to-one correspondence between perpendicular ion acceleration and a particular type of plasma wave within the O(+) source region below 2000 km. In this paper we demonstrate that intense (100-300 mV/m) lower hybrid waves are responsible for transversely accelerating H(+) and O(+) ions to characteristic energies of up to 6 eV. This wave-particle interaction takes place in thin filamentary density cavities oriented along geomagnetic field lines. The measurements we discuss were conducted in the nightside auroral zone at latitudes between 500 km and 1100 km. Our results are consistent with theories of lower hybrid wave condensation and collapse.

Vago, J. L.↗

NASA NTRS1992

Delaminations in composite plates under transverse static loads - Experimental results

Tests were performed measuring the damage initiation loads and the locations, shapes, and sizes of delaminations in Fiberite T300/976 graphite/epoxy, Fiberite IM7/977-2 graphite-toughened epoxy, and ICI APC-2 graphite-PEEK plates subjected to transverse static loads. The data were compared to the results of the Finn-Springer model, and good agreements were found between the measured and calculated delamination lengths and widths.

Finn, Scott R.↗

NASA NTRS1993

Transverse flexural tests as a tool for assessing damage to PMR-15 composites from isothermal aging in air at elevated temperatures

Bowles, Kenneth J.↗

NASA NTRS1991

Transverse ductility of metal matrix composites

The role of the fiber matrix interface bond on the transverse ductility of continuous fiber reinforced composites has been investigated. Two specific systems have been considered: an Aluminum alloy matrix reinforced by Alumina fibers, characterized by a strong interface and a Titanium alloy reinforced by coated Silicon Carbide fibers, characterized by a weak interface. A micro-mechanical study indicates that the bond condition has a significant effect on the state of stress in the matrix which in turn dictates the available matrix ductility. The micro-mechanical predictions are in good agreement with the experimental results for the two systems.

Gunawardena, S. R.↗

NASA NTRS1993

Delaminations in composite plates under transverse static or impact loads - A model

A method is presented for calculating the locations, shapes, and sizes of delaminations which occur in a fiber reinforced composite plate subjected to transverse static or dynamic (impact) loads. The plate may be simply supported, clamped, or free along its edges. A model of the delamination formation was developed. This model was then coupled with a finite element analysis. The model and the finite element analysis were implemented by a computer code which can be used to estimate the load at which damage is initiated as well as the locations, shapes, and sizes of the delaminations.

Finn, Scott R.↗

NASA NTRS1993

Delaminations in composite plates under transverse impact loads - Experimental results

Tests were performed measuring the locations and geometries of delaminations in Fiberite T300/976 graphite/epoxy, Fiberite IM7/977-2 graphite-toughened epoxy, and ICI APC-2 graphite/PEEK plates subjected to transverse impact loads. The data provide specific information on the effects of impactor velocity, impactor mass, material, thickness of back ply group, difference in fiber orientation between adjacent ply groups, plate thickness, and impactor nose radius. The data were compared to the results of the Finn-Springer model. The model was found to describe the data with reasonable accuracy.

Finn, Scott R.↗

NASA NTRS1993

Strong transverse fields in delta-spots

Spectroscopic measurements of the strength and direction of transverse magnetic fields in six delta-spots are presented. The field direction is determined by the relative strength of the pi- and sigma-components at different polarizer orientations, and is, with one exception, parallel to the neutral line and as strong as the umbral field. Field strengths determined by line splitting are as high as 3980 G.

Zirin, Harold↗

NASA NTRS1993

Numerical simulation of plasma processes driven by transverse ion heating

The plasma processes driven by transverse ion heating in a diverging flux tube are investigated with numerical simulation. The heating is found to drive a host of plasma processes, in addition to the well-known phenomenon of ion conics. The downward electric field near the reverse shock generates a doublestreaming situation consisting of two upflowing ion populations with different average flow velocities. The electric field in the reverse shock region is modulated by the ion-ion instability driven by the multistreaming ions. The oscillating fields in this region have the possibility of heating electrons. These results from the simulations are compared with results from a previous study based on a hydrodynamical model. Effects of spatial resolutions provided by simulations on the evolution of the plasma are discussed.

Singh, Nagendra↗

NASA NTRS1993

Universal characteristics of transverse momentum transfer in intermediate energy heavy ion collisions

A microscopic optical model formalism for estimating momentum transfer in intermediate energy heavy ion collisions predicts universal behavior of the transverse component. In particular, for symmetric systems heavier than niobium, it appears that values of P(perpendicular)/A are independent of the mass and charge of the colliding nuclei and vary only with impact parameter and incident beam energy. This suggests that momentum transfer per nucleon saturates to some limiting value with increasing mass.

Khan, F.↗

NASA NTRS1993

Widths of transverse momentum distributions in intermediate-energy heavy-ion collisions

The need to include dynamical collision momentum transfer contributions, arising from interacting nuclear and Coulomb fields, to estimates of fragment momentum distributions is discussed. Methods based upon an optical potential model are presented. Comparisons with recent experimental data of the Siegen group for variances of transverse momentum distributions for gold nuclei at 980 A MeV fragmenting on silver foil and plastic nuclear track detector targets are made. The agreement between theory and experiment is good.

Khan, Ferdous↗

NASA NTRS1935

A deflection formula for single-span beams of constant section subjected to combined axial and transverse loads

In this paper there is presented a deflection formula for single-span beams of constant section subjected to combined axial and transverse loads of the types commonly encountered in airplane design. The form of the equation is obtainable by dimensional analysis. Tables and curves of the non dimensional coefficients are appended to facilitate the use of the formula. The equation is applied to the determination of the spring constant of a beam. Tables and curves are presented to show the variation of the spring constant with changes in the axial load and position along the beam.

Burke, Walter F↗

NASA NTRS1957

Effect of standing transverse acoustic oscillations on fuel-oxidant mixing in cylindrical combustion chambers

Vapor fuel-oxidant mixing is analyzed for standing transverse acoustic fields simulating those existing in screeching or screaming combustors. The additional mixing due to the acoustic field is shown to be a function of sound pressure and frequency, stream velocity, and turbulence. The effects of these parameters are shown graphically for a realistic range of combustor conditions. The fuel-oxidant ratio at various combustor stations is shown to have a cyclic fluctuation which is in phase with the pressure fluctuations. Possible mechanisms contributing to screech and scream are discussed.

TURBINES, GAS - AFTER-BURNING↗

NASA NTRS1943

Some Investigations of the General Instability of Stiffened Metal Cylinders VI : Stiffened Metal Cylinders Subjected to Combined Bending and Transverse Shear

This is the sixth of a series of reports covering an investigation of the general instability problem by the California Institute of Technology. The first five reports of this series cover investigations of the general instability problem under the loading conditions of pure bending and were prepared under the sponsorship of the Civil Aeronautics Administration. This report and the succeeding reports of this series cover the work done on other loading conditions under the sponsorship of the National Advisory Committee for Aeronautics. This report summarizes the work that has been carried on in the experimental investigation of the problem of general instability of stiffened metal cylinders subjected to combined bending and transverse shear at the C.I.T. This part of the investigation includes tests on 55 sheet-covered specimens.

TESTING MACHINES↗

NASA NTRS1958

Tests of Ring-stiffened Circular Cylinders Subjected to a Transverse Shear Load

Thirty-four circular cylinders stiffened by heavy rings were loaded to failure in combined bending and shear with a transverse shear load. The results are presented in the form of an interaction curve which is applicable to the design of ring-stiffened cylinders that fail as a result of local buckling. (author)

Peterson, James P↗

NASA NTRS1951

On the recording of turbulent longitudinal and transverse fluctuations

A thorough understanding of the turbulent flow movements cannot be arrived at from investigations of the temporal mean values of the flows alone. Study of the fluctuation phenomena themselves is indispensable. Thus turbulence research entered a new promising stage when investigators started performing fluctuation measurements and basing theories on those measurements. The investigations of fluctuations carried out so far refer almost exclusively to the so-called isotropic turbulence. It represents a damping phenomenon; it is the simplest type of turbulence where merely the longitudinal fluctuations need to be measured. However, it is precisely nonisotropic turbulence which involves the most essential problem of the turbulent exchange movement and the turbulent apparent friction. Investigation of nonisotropic turbulence requires measurement of longitudinal and transverse fluctuations.

TURBULENCE MEASURING APPARATUS, HOT-WIRE↗