Engineering topics

Davis, Randall C.

Publications and source records attributed to Davis, Randall C..

16 records

NASA NTRS1994

Program Helps Design Composite Panels

Panel Analysis and Sizing Code (PASCO) computer program developed for buckling and vibration analysis and sizing of prismatic structures having arbitrary cross sections. Intended for analyzing and sizing stiffened panels made of laminated orthotropic materials, and of particular value in analyzing and sizing filamentary composite structures. Macintosh version of PASCO includes interactive, graphic preprocessor called MACPASCO. Main objective to make use of PASCO faster, simpler, and less error-prone. Includes graphical user interface (GUI). PASCO written in FORTRAN IV. MACPASCO written in Macintosh Programmers Workbench 3.0, MPW Pascal 3.0, and MacAPP 2.0.

Lucas, Stephen H.↗

NASA NTRS1994

Preprocessor Program For Use With PASCO

MACPASCO is interactive, graphical preprocessor program designed to make use of Panel Analysis and Sizing Code, PASCO, (COSMIC program numbers LAR-13004, LAR-13164, and LAR-14799) faster, simpler, and less error-prone. Is Macintosh-based preprocessor program that includes graphical user interface (GUI) program to simplify specification of panel geometry, making modeling and analysis of panel designs more efficient and reducing potential for user input errors. Written in Macintosh Programmers Workbench 3.0, MPW Pascal 3.0, and MacAPP 2.0.

Lucas, Stephen H.↗

NASA NTRS1993

An analytically designed subcomponent test to reproduce the failure of a composite wing box beam

A Stiffener Runout Test Specimen (SRTS) has been analyzed and tested to verify the failure scenario for a large composite wingbox beam subcomponent. The SRTS was taken from an undamaged region of the subcomponent that was similar to the failure region of the boxbeam. Extensive analyses were performed to determine the proper load introduction and constraint conditions required for the SRTS test to simulate the response of the subcomponent. The present paper describes the analyses that led to the design of test fixtures that ensured that the response of the SRTS duplicated the response of the box beam. The results of the SRTS test are described and compared with the analytical predictions.

Davis, D. D., Jr.↗

NASA NTRS1992

Technology integration box beam failure study

Composite structures have the potential to be cost effective, structurally efficient primary aircraft structures. As part of the Advanced Composite Technology (ACT) program to exploit this potential for heavily loaded aircraft structures, the design and fabrication of the technology integration box beam (TIBB) was completed. The TIBB is an advanced composite prototype structure for the center wing section of the Lockheed C-130 aircraft. The TIBB was tested for downbending, upbending, torsion, and combined upbending and torsion load conditions to verify the design. The TIBB failed at 83 percent of design ultimate load for the combined upbending and torsion load condition. Current analytical and experimental results are described for a study of the mechanisms that led to the failure of the TIBB. Experimental results include load, strain, and deflection data. An analytical study was conducted of the TIBB structural response. Analytical results include strain and deflection results from a global analysis of the TIBB.

Shuart, Mark J.↗

NASA NTRS1991

User's manual for the Macintosh version of PASCO

A user's manual for Macintosh PASCO is presented. Macintosh PASCO is an Apple Macintosh version of PASCO, an existing computer code for structural analysis and optimization of longitudinally stiffened composite panels. PASCO combines a rigorous buckling analysis program with a nonlinear mathematical optimization routine to minimize panel mass. Macintosh PASCO accepts the same input as mainframe versions of PASCO. As output, Macintosh PASCO produces a text file and mode shape plots in the form of Apple Macintosh PICT files. Only the user interface for Macintosh is discussed here.

Lucas, S. H.↗

NASA NTRS1991

Test of superplastically formed corrugated aluminum compression specimens with beaded webs

Corrugated wall sections provide a highly efficient structure for carrying compressive loads in aircraft and spacecraft fuselages. The superplastic forming (SPF) process offers a means to produce complex shells and panels with corrugated wall shapes. A study was made to investigate the feasibility of superplastically forming 7475-T6 aluminum sheet into a corrugated wall configuration and to demonstrate the structural integrity of the construction by testing. The corrugated configuration selected has beaded web segments separating curved-cap segments. Eight test specimens were fabricated. Two specimens were simply a single sheet of aluminum superplastically formed to a beaded-web, curved-cap corrugation configuration. Six specimens were single-sheet corrugations modified by adhesive bonding additional sheet material to selectively reinforce the curved-cap portion of the corrugation. The specimens were tested to failure by crippling in end compression at room temperature.

Davis, Randall C.↗

NASA NTRS1990

A parametric shell analysis of the shuttle 51-L SRB AFT field joint

Following the Shuttle 51-L accident, an investigation was conducted to determine the cause of the failure. Investigators at the Langley Research Center focused attention on the structural behavior of the field joints with O-ring seals in the steel solid rocket booster (SRB) cases. The shell-of-revolution computer program BOSOR4 was used to model the aft field joint of the solid rocket booster case. The shell model consisted of the SRB wall and joint geometry present during the Shuttle 51-L flight. A parametric study of the joint was performed on the geometry, including joint clearances, contact between the joint components, and on the loads, induced and applied. In addition combinations of geometry and loads were evaluated. The analytical results from the parametric study showed that contact between the joint components was a primary contributor to allowing hot gases to blow by the O-rings. Based upon understanding the original joint behavior, various proposed joint modifications are shown and analyzed in order to provide additional insight and information. Finally, experimental results from a hydro-static pressurization of a test rocket booster case to study joint motion are presented and verified analytically.

Davis, Randall C.↗

NASA NTRS1990

Superplastically Formed Titanium Hat-Stiffened Panels

Recent advances in superplastic forming of some metals make it possible to fabricate new shapes. Superplastic forming enables design of structures using mass more efficiently. Parts having intersecting compound contour surfaces made; impossible to fabricate such parts by more conventional methods. Beaded hat-stiffened panel has higher critical buckling strain than conventional hat-stiffened panel.

Davis, Randall C.↗

NASA NTRS1988

Cryogenic Insulation System

This invention relates to reusable, low density, high temperature cryogenic foam insulation systems and the process for their manufacture. A pacing technology for liquid hydrogen fueled, high speed aircraft is the development of a fully reusable, flight weight cryogenic insulation system for propellant tank structures. In the invention cryogenic foam insulation is adhesively bonded to the outer wall of the fuel tank structure. The cryogenic insulation consists of square sheets fabricated from an array of abutting square blocks. Each block consists of a sheet of glass cloth adhesively bonded between two layers of polymethacrylimide foam. Each block is wrapped in a vapor impermeable membrane, such as Kapton(R) aluminum Kapton(R), to provide a vapor barrier. Very beneficial results can be obtained by employing the present invention in conjunction with fibrous insulation and an outer aeroshell, a hot fuselage structure with an internal thermal protection system.

Davis, Randall C.↗

NASA NTRS1988

Truss-Core Corrugation

Strength-to-weight ratio exceeds beaded-web design by 60 percent. New corrugation design offers significant weight saving. Truss-core web replaces beaded web of previous corrugation designs.

Davis, Randall C.↗

NASA NTRS1988

Direct solution for thermal stresses in a nose cap under an arbitrary axisymmetric temperature distribution

The design of a nose cap for a hypersonic vehicle is an iterative process requiring a rapid, easy to use and accurate stress analysis. The objective of this paper is to develop such a stress analysis technique from a direct solution of the thermal stress equations for a spherical shell. The nose cap structure is treated as a thin spherical shell with an axisymmetric temperature distribution. The governing differential equations are solved by expressing the stress solution to the thermoelastic equations in terms of a series of derivatives of the Legendre polynomials. The process of finding the coefficients for the series solution in terms of the temperature distribution is generalized by expressing the temperature along the shell and through the thickness as a polynomial in the spherical angle coordinate. Under this generalization the orthogonality property of the Legendre polynomials leads to a sequence of integrals involving powers of the spherical shell coordinate times the derivative of the Legendre polynomials. The coefficients of the temperature polynomial appear outside of these integrals. Thus, the integrals are evaluated only once and their values tabulated for use with any arbitrary polynomial temperature distribution.

Davis, Randall C.↗

NASA NTRS1987

Reusable High-Temperature/Cryogenic Foam-Insulation System

Flightweight insulation withstands wide temperture cycling. Reusable insulation system for cryogenic containment vessels withstands repeated exposures to thermal environments that span ranges from cryogenic-fluid temperature {-425oF (-254oC)} to maximum use temperature of containment-tank material {+400oF (+204oC)}. System designed for use with high-speed flight vehicles.

Davis, Randall C.↗

NASA NTRS1987

Daze fasteners

A daze fastener system for connecting two or more structural elements wherein the structural elements and fastener parts have substantially different coefficient of thermal expansion physical property characteristics is employed in this invention. By providing frusto-conical abutting surfaces between the structural elements and fastener parts any differences in thermal expansion/contraction between the parts is translated to sliding motion and avoids deleterious thermal stresses in the connection. An essential feature for isotropic homogeneous material connections is that at least two sets of mating surfaces are required wherein each set of mating surfaces has line element extensions that pass through a common point.

Jackson, L. Robert↗

NASA NTRS1987

Buckling tests of a 10 foot diameter stiffened cylinder with rectangular cutouts

A 10-foot diameter aluminum cylinder with rectangular cutouts in its ring and stringer stiffened wall was loaded to failure by an end bending moment. A 24x27 inch cutout, centered on the compression side of the shell, was first cut into the cylinder. After testing, the cutout area was enlarged to a 36/36 inch square cutout that removed the material damaged by buckling during the first test. After the second buckling test, the cutout area was patched with an equivalent stiffness plate bolted over the cutout hole. The cylinder was rotated 120 deg. and a 18x18 inch square hole cut into the center of the new compression side of the shell. Test specimen details, test procedures, and test results are presented.

Davis, Randall C.↗

NASA NTRS1987

Analysis and test of superplastically formed titanium hat-stiffened panels under compression

Four hat-stiffened titanium panels with two different stiffener configurations were fabricated by superplastic forming/weld brazing and tested under a moderately heavy compressive load. The panels had the same overall dimensions but differed in the shape of the hat-stiffener webs; three panels had stiffeners with flat webs and the other panel had stiffeners with beaded webs. Analysis indicated that the local buckling strain of the flat stiffener web was considerably lower than the general panel buckling strain or cap buckling strain. The analysis also showed that beading the webs of the hat stiffeners removed them as the critical element for local buckling and improved the buckling strain of the panels. The analytical extensional stiffness and failure loads compared very well with experimental results.

Davis, Randall C.↗

NASA NTRS1987

Superplastic forming/weld-brazing of Ti-6Al-4V panels for enhanced structural efficiency

An account is given of the results obtained by NASA-sponsored studies which exploit the processing advantages of superplastic forming (SPF) and joining by weld-brazing (WB) for the fabrication of Ti-alloy skin-stiffened structural components. The buckling strengths of panels with stiffeners having the geometry of a conventional hat shape are compared with those of panels having advanced-geometry stiffereners. Both single- and multiple-stiffened panels have been evaluated at room temperature; the SPF/WB panels with advanced-geometry stiffeners developed up to 60-percent higher buckling strength than panels with conventional-geometry stiffeners. Selective stiffener reinforcement with a boron-reinforced Al-matrix MMC was also evaluated.

Royster, Dick M.↗