Engineering topics

Starnes, J. H., Jr.

Publications and source records attributed to Starnes, J. H., Jr..

At least 37 records · Page 2

NASA NTRS1985

A nonlinear analysis of infinitely long graphite-epoxy cylindrical panels loaded with internal pressure

The structural response of internally pressurized composite cylindrical panels, representative of a transport aircraft's fuselage skins, is predicted by means of a one-dimensional, geometrically nonlinear analysis. An analytical study is conducted for the response of 4-, 8-, and 16-ply graphite/epoxy skins. The results obtained indicate that the response is geometrically nonlinear, and that a boundary layer with a severe bending gradient exists at the panel edges. The importance of through-the-thickness shearing deformations in the bending boundary layer is illustrated through comparison of analyses based on Kirchhoff-Love and shear deformation theories. Numerical results for the bending boundary layer lengths of the different panels are presented, and two bending boundary layers are predicted with the shear deformation theory.

Boitnott, R. L.↗

NASA NTRS1985

The effect of slots on the buckling and postbuckling behavior of laminated plates

An experimental study was conducted to evaluate the effect of lateral slots on the buckling response, the postbuckling response, and the failure characteristics of flat rectangular graphite-epoxy plates loaded in compression. The slots did not significantly affect the prebuckling and buckling behavior of the plates. The slots caused local changes in the strain distribution and out-of-plane deformations near the slot. Failure loads and modes were strongly affected by slot location. Centrally located slots did not affect the failure loads or failure modes of the plates. Slots located close to an unloaded edge of a plate reduced the postbuckling strength of the plate and affected the failure mode. For one slightly offset slot location, interaction of out-of-plane deformations with the slot tip was observed to affect the failure mode significantly without affecting the failure load.

Gurdal, Z.↗

NASA NTRS1984

Postbuckling behavior of graphite-epoxy panels

Structurally efficient fuselage panels are often designed to allow buckling to occur at applied loads below ultimate. Interest in applying graphite-epoxy materials to fuselage primary structure led to several studies of the post-buckling behavior of graphite-epoxy structural components. Studies of the postbuckling behavior of flat and curved, unstiffened and stiffened graphite-epoxy panels loaded in compression and shear were summarized. The response and failure characteristics of specimens studied experimentally were described, and analytical and experimental results were compared. The specimens tested in the studies described were fabricated from commercially available 0.005-inch-thick unidirectional graphite-fiber tapes preimpregnated with 350 F cure thermosetting epoxy resins.

Starnes, J. H., Jr.↗

NASA NTRS1984

Postbuckling behavior of axially compressed graphite-epoxy cylindrical panels with circular holes

The results of an experimental and analytical study of the effects of circular holes on the postbuckling behavior of graphite-epoxy cylindrical panels loaded in axial compression are presented. The STAGSC-1 general shell analysis computer code is used to determine the buckling and postbuckling response of the panels. The loaded, curved ends of the specimens were clamped by fixtures and the unloaded, straight edges were simply supported by knife-edge restraints. The panels are loaded by uniform end shortening to several times the end shortening at buckling. The unstable equilibrium path of the postbuckling response is obtained analytically by using a method based on controlling an equilibrium-path-arc-length parameter instead of the traditional load parameter. The effects of hole diameter, panel radius, and panel thickness on postbuckling response are considered in the study. Experimental results are compared with the analytical results and the failure characteristics of the graphite-epoxy panels are described.

Knight, N. F., Jr.↗

NASA NTRS1984

Nonlinear response and failure characteristics of clamped internally pressurized graphite-epoxy cylindrical panels

The nonlinear response and failure characteristics of internally pressurized 4- to 16-ply cylindrical panels of graphite/epoxy are experimentally and analytically studied. Tests simulated the skin of a typical transport aircraft fuselage under loading to eventual failure. Aluminum test specimens were similarly tested and compared. All graphite/epoxy panels are found to withstand the internal pressures applied, which are well above the proof pressure loading expected for transport fuselage structures.

Boitnott, R. L.↗

NASA NTRS1983

Failure Analysis and Mechanisms of Failure of Fibrous Composite Structures

The state of the art of failure analysis and current design practices, especially as applied to the use of fibrous composite materials in aircraft structures is discussed. Deficiencies in these technologies are identified, as are directions for future research.

Noor, A. K.↗

NASA NTRS1983

Design for global damage tolerance and associated mass penalties

A structural design with global damage tolerance is defined as a design that can tolerate the destruction of one or more major structural components. The mass penalty associated with improving the global damage tolerance of optimized structures is evaluated herein for structures typically used in aircraft wing construction. It is shown that this mass penalty is strongly related to the degree of redundancy of the structure, being most severe for structures of low redundancy. For highly redundant wing-box structures made of composite materials, it is shown that significant improvement in global damage tolerance may be achieved without any mass penalty.

Haftka, R. T.↗

NASA NTRS1983

Failure characteristics of graphite-epoxy structural components loaded in compression

Failure characteristics of compressively loaded graphite-epoxy components are described. Experimental results for both strength-critical laminates and structural components with postbuckling strength are presented. Effects of low speed impact damage and circular holes on compressive strength are discussed. Delamination and shear crippling failure mechanisms that limit the performance of strength-critical laminates are described. Transverse shear and skin-stiffener separation failure mechanisms that limit the performance of components with postbuckling strength are also described. The influence of matrix properties on compressive strength improvements for impact damaged laminates is discussed. Experimental data and results from a failure analysis for strength-critical laminates with cutouts are discussed and compared with impact damage results. Typical postbuckling test results are compared with analytical predictions. Previously announced in STAR as N83-12174

Starnes, J. H., Jr.↗

NASA NTRS1982

Failure characteristics of graphite-epoxy structural components loaded in compression

Starnes, J. H., Jr.↗

NASA NTRS1982

Design detail verification tests for a lightly loaded open-corrugation graphite-epoxy cylinder

Flat corrugated graphite-epoxy panels were tested in compression to verify selected design details of a ring-stiffened cylinder that was designed to support an axial compressive load of 157.6 kN/m without buckling. Three different sizes of subcomponent panels, with the same basic corrugation geometry, were tested: (1) 60.96-cm-long by 45.72-cm-wide panels to evaluate the local buckling strength of the shell wall design; (2) 91.44-cm-long by 45.72-cm-wide panels to evaluate a longitudinal joint and the load-introduction method; and (3) 254.0-cm-long by 91.44-cm-wide panels with four simulated-ring stiffeners to evaluate the ring-attachment method. The test results indicate that the modified shell-wall design, the longitudinal joint, the load-introduction method, and the stiffener-attachment method for the proposed cylinder have adequate strength to support the design load.

Davis, R. C.↗

NASA NTRS1982

Postbuckling behavior of selected flat stiffened graphite-epoxy panels loaded in compression

Results of an experimental study of the postbuckling behavior of selected flat stiffened graphite-epoxy panels loaded in compression are presented. The postbuckling response and failure characteristics of undamaged panels and panels damaged by low-speed impact are described. Each panel had four equally-spaced I-spaced stiffeners and 16- or 24-ply quasi-isotropic skins. Panels with three different stiffener spacings were tested. Some undamaged specimens supported as much as three times their initial buckling load before failing. Failure of all panels initiated in a skin-stiffener interface region. Analytical results obtained from a nonlinear general shell finite element analysis computer code correlate well with typical postbuckling test results up to failure. The analytical modeling detail necessary to predict accurately the response of a panel is described. Test results show that low-speed impact damage can reduce the postbuckling strength of a stiffened panel and that the skin-stiffener interface region is more sensitive to impact damage than the skin midway between stiffeners.

Starnes, J. H., Jr.↗

NASA NTRS1981

Postbuckling and failure characteristics of selected flat rectangular graphite-epoxy plates loaded in compression

Results of an experimental study of the postbuckling response and failure characteristics of 16- and 24-ply quasi-isotropic and 24-ply orthotropic flat rectangular graphite-epoxy plates loaded in compression are examined. Some of the specimens had circular drilled holes or were subjected to low-speed impact damage. The ratio of failure load to buckling load was found to be higher for specimens with lower initial buckling strains than for specimens with higher initial buckling strains. Some specimens supported more than five times their initial buckling load before failing. The specimens failed along a nodal line of the buckling mode in an induced shear failure mode. Holes and impact damage had a more adverse effect on the postbuckling strength of specimens with high initial buckling strains than on the strength of specimens with lower initial buckling strains.

Starnes, J. H., Jr.↗

NASA NTRS1980

Buckling and postbuckling research on flat and curved composite panels

Progress in the development of verified design technology for generic advanced-composite structural components loaded in compression is reported. Generic structural configurations material systems and load ranges of interest for a given application were investigated using structural procedures, structural analysis procedures, and laboratory testing of structural specimens. Both flat and curved composite compression panels that are designed either to be buckling resistant or to have postbuckling strength depending on the expected application of the panels were considered.

Starnes, J. H., Jr.↗

NASA NTRS1980

Preliminary design of composite wing-box structures for global damage tolerance

A procedure is presented that incorporates the influence of potential global damage conditions into the design process for minimum-mass wing-box structures. The procedure is based on mathematical-programming optimization techniques. Material-strength, minimum-gage, and panel-buckling constraints are introduced by penalty functions, and Newton's method with approximate second derivatives of the penalty terms is used as the search algorithm to obtain minimum-mass designs. A potential global damage condition is represented by a structural model with the damaged components removed. Example minimum-mass designs are obtained that simultaneously satisfy the constraints of the damaged and undamaged configurations of both graphite-epoxy and aluminum wing-box structural models. These examples are designed with and without the influence of potential damage conditions, and results indicate that for equal mass cases the residual strength of a damaged structure is higher when the influence of potential damage is properly included in the design from the outset. Results of these examples also identify the minimum structural mass increase required to increase residual strength levels.

Starnes, J. H., Jr.↗

NASA NTRS1980

Recent developments in the design, testing and impact-damage tolerance of stiffened composite panels

The structural technology of laminated filamentary-composite stiffened-panel structures under combined in-plane and lateral loadings is discussed. Emphasis is on analyzing the behavior of the structures under load, determining appropriate structural proportions for weight efficient configurations, and effects of impact damage and geometric imperfections on structural performance. Experimental data on buckling of panels under in-plane compression validate the analysis and sizing methods, and illustrate structural performance and efficiency obtained from representative structures. It is shown that the strength of panels under in-plane compression can be degraded by low-velocity impact damage, and data are presented which indicate that the matrix is a significant factor influencing tolerance to impact damage.

Williams, J. G.↗

NASA NTRS1979

Recent development in the design, testing and impact-damage tolerance of stiffened composite panels

Structural technology of laminated filamentary-composite stiffened-panel structures under combined inplane and lateral loadings is discussed. Attention is focused on: (1) methods for analyzing the behavior of these structures under load and for determining appropriate structural proportions for weight-efficient configurations; and (2) effects of impact damage and geometric imperfections on structural performance. Recent improvements in buckling analysis involving combined inplane compression and shear loadings and transverse shear deformations are presented. A computer code is described for proportioning or sizing laminate layers and cross-sectional dimensions, and the code is used to develop structural efficiency data for a variety of configurations, loading conditions, and constraint conditions. Experimental data on buckling of panels under inplane compression is presented. Mechanisms of impact damage initiation and propagation are described.

Williams, J. G.↗

NASA NTRS1979

Low-velocity impact damage in graphite-fiber reinforced epoxy laminates

An experimental investigation was conducted to identify the failure mechanisms and to understand damage propagation in compression-loaded composite structures. The tests were conducted on several laminates of different ply orientation with thickness that ranged from 0.56 to 0.75 cm. The panels were damaged by 1.27-cm-diameter aluminum spheres propelled normal to the specimen surface at velocities ranging from 30 m/s to 140 m/s. Results indicate that there is significant internal laminate damage due to low-velocity impact with no surface damage. The internal damage consists of delamination and intraply cracking. Three damage propagation modes were identified as causing specimen failure; which are delamination, axial load-lateral deformation coupling, and local shear failure.

Rhodes, M. D.↗

NASA NTRS1979

Effect of impact damage and holes on the compressive strength of a graphite/epoxy laminate

An experimental investigation has been conducted to determine the effect of low-velocity impact damage and unloaded circular holes on the compressive strength of a 48-ply orthotropic graphite/epoxy flat laminate. Specimens were impacted by a 1.27-cm-diameter aluminum sphere with speeds from 52 to 101 m/x to simulate momenta typical of low-velocity impact hazards that can occur in commercial aircraft service. It is shown that low-velocity impact damage can significantly degrade the static compressive strength of the laminate. Specimens that fail at axial strains above 0.008 in the undamaged condition can fail at strains as low as 0.0031 when impacted at 100 m/s. Circular holes also reduce the static compressive strength of the laminate. The failure strain decreases as the hole diameter increases.

Starnes, J. H., Jr.↗