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At least 37 records · Page 2

Stress-concentration factors for finite orthotropic laminates with a circular hole and uniaxial loading

Stresses were calculated for finite-width orthotropic laminates with a circular hole and remote uniaxial loading using a two-dimensional finite element analysis with both uniform stress and uniform displacement boundary conditions. Five different laminates were analyzed. Computed results are presented for selected combinations of hole diameter/sheet-width ratio d/w and length-to-width ratio L/w. For small L/w values, the stress-concentration factors K sub tn were significantly different for the uniform stress and uniform displacement boundary conditions. Typically, for the uniform stress condition, the K sub tn values were much larger than for the infinite strip reference condition; however, for the uniform displacement condition, they were only slightly smaller than for this reference. The results for long strips are also presented as width correction factors. For d/w less or = 0.33, these width correction factors are nearly equal for all five laminates.

Hong, C. S.↗

Analysis of a slot loaded microstrip disk antenna for circular polarisation

A method is presented to analyze a circular microstrip disk antenna loaded with a narrow, inclined slot at its center and fed by a coaxial probe. Making use of the exact dyadic Green's functions for a grounded dielectric slab due to electric and magnetic currents, Richmond's reaction integral equation in conjunction with the method of moments (Galerkin), a generalized h-parameter equivalent network for the loaded patch is obtained. An expression for the input impedance of a slot loaded microstrip patch is obtained from the equivalent parameters. The theoretical results are compared with the experiment.

Rao, Y. R.↗

Three-Dimensional Postbuckling Analysis of Curved Beams

Presented here is a method of solving highly flexible curved beam undergoing huge static or quasi-static deformations. A geometrically exact beam theory based on the use of Jaumann stresses and strains and exact coordinate transformation is presented in terms of 17 first-order ordinary differential equations, and a multiple shooting method is used to solve the corresponding nonlinear two-point boundary value problems. The geometrically exact beam theory accounts far large rotations, large displacements, initial curvatures, extensionality, and transverse shear strains. Four examples are used to demonstrate this method, including a rotating clamped-free beam under the influence of gravity and centrifugal forces, an L-frame subjected to an in-plane tip load, a circular arch subjected to a concentrated load, and a clamped-hinged helical spring subjected to an axial displacement. Results show that the combination of the multiple shooting method and the geometrically exact beam theory works very well. Moreover, the obtained numerically exact solutions can be used to verify the accuracy of nonlinear finite element codes for nonlinear analysis of complex structures.

Pai, P. Frank↗

Aerodynamic Forces and Loadings on Symmetrical Circular-Arc Airfoils with Plain Leading-Edge and Plain Trailing-Edge Flaps

An investigation has been made in the Langley two-dimensional low-turbulence tunnel and in the Langley two-dimensional low-pressure tunnel of 6- and 10-percent-thick symmetrical circular-arc airfoil sections at low Mach numbers and several Reynolds numbers. The airfoils were equipped with 0.15-chord plain leading-edge flaps and 0.20-chord plan trailing-edge flaps. The section lift and pitching-moment characteristics were determined for both airfoils with the flaps deflected individually and in combination. The section drag characteristics were obtained for the 6-percent-thick airfoil with the flaps partly deflected as low-drag-control flaps and for airfoils with the flaps neutral. Surface pressures were measured on the 6-percent-thick airfoil section with the flaps deflected either individually or in appropriate combination to furnish flap load and hinge-moment data applicable to the structural design of the airfoil. A generalized method is developed that permits the determination of the chordwise pressure distribution over sharp-edge airfoils with plain leading-edge flaps and plain trailing-edge flaps of arbitrary size and deflection.

Cahill, Jones F↗

Flush-mounted dielectric-loaded axial slot on circular cylinder

The theory, computer program, and numerical results of an investigation of an axial slot antenna on a circular cylinder are discussed. The cylinder is partially coated with a dielectric layer and the antenna radiates through a flush mounted window. The study was conducted to determine the effects of a high temperature dielectric layer on the performance of antennas mounted on a space shuttle. Mathematical models are developed to show the relationships of the parameters. Curves are developed to compare the theoretical and actual far field radiation patterns.

Richmond, J. H.↗

Flush-mounted dielectric-loaded axial slot on circular cylinder

An investigation is conducted of electric field patterns of a TE axial slot antenna which radiates through a dielectric window in a circular cylinder. The cylinder is partially coated with a dielectric layer. The investigation is to provide information regarding the effects of a high-temperature dielectric layer on the performance of antennas mounted on a space shuttle. Numerical results are presented for the far-field patterns. It is pointed out that the calculations show excellent agreement with experimental measurements.

Richmond, J. H.↗

Failure mechanisms of uni-ply composite plates with a circular hole under static compressive loading

The objective of the study was to identify and study the failure mechanisms associated with compressive-loaded uniply graphite/epoxy square plates with a central circular hole. It is found that the type of compressive failure depends on the hole size. For large holes with the diameter/width ratio exceeding 0.062, fiber buckling/kinking initiated at the hole is found to be the dominant failure mechanism. In plates with smaller hole sizes, failure initiates away from the hole edge or complete global failure occurs. Critical buckle wavelengths at failure are presented as a function of the normalized hole diameter.

Khamseh, A. R.↗