Engineering topics

Biggers, Sherrill B.

Publications and source records attributed to Biggers, Sherrill B..

6 records

NASA NTRS1994

Shear buckling response of tailored composite plates

This Note evaluates the piecewise-uniform approach to tailoring as a mean of improving the shear buckling loads of composite plates. This design approach is referred to herein as stiffness tailoring or, more simply, as tailoring. The primary objectives are to determine the tailoring patterns and the degree of concentration of the material used to achieve the tailoring in each pattern that maximize the shear buckling load and to quantify the maximum relative improvement that can be achieved in the buckling load compared to uniform plates.

Biggers, Sherrill B.↗

NASA NTRS1993

Compression buckling response of tailored rectangular composite plates

Buckling resistance is often a controlling criterion in the design of structures composed of plate elements. Design concepts that lead to increased buckling loads (or strains) of these plate elements can directly lower the structural cost and/or weight by a number of means. This study quantifies the improvements that can be achieved in compression buckling loads of rectangular composite plates by using a simple stiffness-tailoring concept. The approach is to position the unidirectional lamina through the thickness and over the planform of the plate so that the buckling load is increased with no loss in in-plane stiffness or increase in weight. Finite element analyses have been used to determine the effects of tailoring on the buckling loads of plates with various boundary conditions, aspect ratios, thicknesses, and membrane stiffnesses. Increases in buckling loads (or strains) of 200 percent or more compared to the uniform plate-buckling loads are shown possible with this tailoring concept.

Biggers, Sherrill B.↗

NASA NTRS1993

Shear buckling response of tailored, rectangular, composite plates

The concept of stiffness tailoring for improved shear buckling resistance of rectangular composite plates is investigated analytically. The tailoring involves only the redistribution of the given material with given orientations to create beneficial stiffening patterns across the planform of the plate. The resulting local nonuniformities in thickness and membrane and bending stiffness combine to change the buckling response of the plate. The weight and average membrane shear stiffness are essentially unaffected by the tailoring. Practical limitations on the degree to which the tailoring may be carried out are shown to govern most designs. Improvements in the shear buckling load on the order of 50 percent are shown possible with monolithic tailoring. Tailored sandwich concepts, in which a light-weight core material is added to keep both plate surfaces flat, can produce improvements well over 100 percent in specific buckling loads compared with uniform composite plates.

Biggers, Sherrill B.↗

NASA NTRS1991

Improved compression buckling for rectangular composite plates by stiffness tailoring

Buckling resistance is often a controlling criterion in the design of structural elements. Design concepts that lead to increased buckling loads (or strains) can directly lower the structural cost and/or weight by a number of means. This study quantifies the improvements that can be achieved in compression buckling loads of rectangular composite plates by using a simple stiffness tailoring concept. The approach is to position the unidirectional lamina through the thickness and over the planform of the plate so that the buckling load is increased with no loss in in-plane stiffness or increase in weight. Finite element analyses have been used to determine the effects of tailoring on the buckling load of plates with various boundary conditions, aspect ratios, thicknesses, and membrane stiffnesses. Increases in buckling loads (or strains) of nearly 200 percent over the uniform plate buckling loads are shown possible with this tailoring concept.

Biggers, Sherrill B.↗

NASA NTRS1990

A Protection And Detection Surface (PADS) for damage tolerance

A protection and detection surface (PADS) concept was studied for application to composite primary aircraft structures. A Kevlar-epoxy woven face sheet with a Rohacell foam core was found to be the most effective PADS configuration among the configurations evaluated. The weight of the PADS configuration was estimated to be approximately 17 pct of the structural weight. The PADS configuration was bonded to graphite-epoxy base laminates, and up to a 70 pct improvement in compression-after-impact failure strains was observed.

Shuart, Mark J.↗

NASA NTRS1985

Stiffener attachment concepts for graphite-epoxy panels designed for postbuckling strength

Stiffener attachment concepts for suppressing or delaying the onset of the skin-stiffener separation failure mode in graphite-epoxy compression panels designed for postbuckling strength were experimentally studied. The effectiveness of these concepts was evaluated using panels with 16-ply skins and a single centrally-located I-shaped stiffener with both static and cyclic compressive loadings. Analytical results suggest that tailoring the relative thicknesses of the panel skin, stiffener attachment flange, and the stiffener web rotational stiffness can minimize the adverse effects of high interface shear and normal stresses. Interface stress levels may be reduced by tapering the thickness of the stiffener attachment flange and properly selecting the stacking sequences of the skin and stiffener attachment flange laminates.

Dickson, John N.↗