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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Wave propagation and impact in composite materials

Anisotropic waves in composites are considered, taking into account wave speeds, wave surfaces, flexural waves in orthotropic plates, surface waves, edge waves in plates, and waves in coupled composite plates. Aspects of dispersion in composites are discussed, giving attention to pulse propagation and dispersion, dispersion in rods and plates, dispersion in a layered composite, combined material and structural dispersion, continuum theories for composites, and variational methods for periodic composites. The characteristics of attenuation and scattering processes are examined and a description is given of shock waves and impact problems in composites. A number of experiments are also reported.

Moon, F. C.↗
NASA NTRS1983

Viscoelastic study of an adhesively bonded joint

The plane strain problem of two dissimilar orthotropic plates bonded with an isotropic, linearly viscoelastic adhesive is considered. Both the shear and the normal stresses in the adhesive are calculated for various geometries and loading conditions. Transverse shear deformations of the adherends are taken into account, and their effect on the solution is shown in the results. All three inplane strains of the adhesive are included. Attention is given to the effect of temperature, both in the adhesive joint problem and to the heat generation in a viscoelastic material under cyclic loading. This separate study is included because heat generation and or spatially varying temperature are at present too difficult to account for in the analytical solution of the bonded joint, but whose effect can not be ignored in design.

Joseph, P. F.↗
NASA NTRS1984

Buckling loads of stiffened panels subjected to combined longitudinal compression and shear: Results obtained with PASCO, EAL, and STAGS computer programs

Buckling analyses used in PASCO are summarized with emphasis placed on the shear buckling analyses. The PASCO buckling analyses include the basic VIPASA analysis, which is essentially exact for longitudinal and transverse loads, and a smeared stiffener solution, which treats a stiffened panel as an orthotropic plate. Buckling results are then presented for seven stiffened panels loaded by combinations of longitudinal compression and shear. The buckling results were obtained with the PASCO, EAL, and STAGS computer programs. The EAL and STAGS solutions were obtained with a fine finite element mesh and are very accurate. These finite element solutions together with the PASCO results for pure longitudinal compression provide benchmark calculations to evaluate other analysis procedures.

Stroud, W. J.↗
NASA NTRS1985

Fracture analysis of notched composites

The problem of part-through cracks emanating from a central notch in a composite laminate is considered. The composite laminate is modeled as an orthotropic plate and along the branches, it is assumed that the stresses are carried by the fibers only. The stresses along the uncracked portions are assumed to be proportional to the crack opening displacement at the point. After formulating the branched crack problem, the model is applied to a(+45 deg)25 composite laminate. The stress concentration factors for the fibers are computed for various values of the spring constant K. Sample results showing the crack opening displacement are also displayed.

Deale, F.↗
NASA NTRS1985

Fracture analysis of notched composites

In this study the problem of part-through cracks emanating from a central notch in a composite laminate is considered. The composite laminate is modeled as an orthotropic plate and along the branches, it is assumed that the stresses are carried by the fibers only. The stresses along the uncracked portions are assumed to be proportional to the crack opening displacement at that point. After formulating the branched crack problem, the model is applied to a (4 + or - 45 deg) 2s composite laminate. The stress concentration factors for the fibers are computed for various values of the spring constant K.

Delale, F.↗
NASA NTRS1990

Low velocity impact analysis with NASTRAN

A nonlinear elastic force-displacement relationship is used to calculate the transient impact force and local deformation at the point of contact between impactor and target. The nonlinear analysis and transfer function capabilities of NASTRAN are used to define a finite element model that behaves globally linearly elastic, and locally nonlinear elastic to model the local contact behavior. Results are presented for two different structures: a uniform cylindrical rod impacted longitudinally; and an orthotropic plate impacted transversely. Calculated impact force and transient structural response of the targets are shown to compare well with results measured in experimental tests.

Trowbridge, Daniel A.↗
NASA NTRS1990

Low velocity impact analysis with NASTRAN

A nonlinear elastic force-displacement relationship is used to calculate the transient impact force and local deformation at the point of contact between impactor and target. The nonlinear analysis and transfer function capabilities of NASTRAN are used to define a finite element model that behaves globally linearly elastic, and locally nonlinear elastic to model the local contact behavior. Results are presented for two different structures: a uniform cylindrical rod impacted longitudinally; and an orthotropic plate impacted transversely. Calculated impact force and transient structural response of the targets are shown to compare well with results measured in experimental tests.

Trowbridge, Daniel A.↗
NASA NTRS1991

Low velocity impact analysis with NASTRAN

A nonlinear elastic force-displacement relationship is used to calculate the transient impact force and local deformation at the point of contact between impactor and target. The nonlinear analysis and transfer function capabilities of NASTRAN are used to define a finite element model that behaves globally linearly elastic, and locally nonlinear elastic to model the local contact behavior. Results are presented for two different structures: a uniform cylindrical rod impacted longitudinally; and an orthotropic plate impacted transversely. Calculated impact force and transient structural response of the targets are shown to compare well with results measured in experimental tests.

Trowbridge, D. A.↗
NASA NTRS1993

The effects of stress and physical aging on the creep compliance of a polymeric composite

An experimental study was performed to determine the effects of stress and physical aging on the matrix dominated viscoelastic properties of IM7/8320, a high temperature fiber reinforced thermoplastic composite. Established creep/aging test techniques developed for polymers were adapted for testing of the composite material. The transverse and shear compliance for an orthotropic plate were found from creep compliance measurements at constant, sub-Tg temperatures. These compliance terms were shown to be effected by physical aging. Aging time shift factors and shift rates were found to be a function of applied stress.

Gates, Thomas E.↗
NASA NTRS1993

Time dependent behavior of a graphite/thermoplastic composite and the effects of stress and physical aging

Two complimentary studies were performed to determine the effects of stress and physical aging on the matrix dominated time dependent properties of IM7/8320 composite. The first of these studies, experimental in nature, used isothermal tensile creep/aging test techniques developed for polymers and adapted them for testing of the composite material. From these tests, the time dependent transverse (S22) and shear (S66) compliance's for an orthotropic plate were found from short term creep compliance measurements at constant, sub-T(sub g) temperatures. These compliance terms were shown to be affected by physical aging. Aging time shift factors and shift rates were found to be a function of temperature and applied stress. The second part of the study relied upon isothermal uniaxial tension tests of IM7/8320 to determine the effects of physical aging on the nonlinear material behavior at elevated temperature. An elastic/viscoplastic constitutive model was used to quantify the effects of aging on the rate-independent plastic and rate-dependent viscoplastic response. Sensitivity of the material constants required by the model to aging time were determined for aging times up to 65 hours. Verification of the analytical model indicated that the effects of prior aging on the nonlinear stress/strain/time data of matrix dominated laminates can be predicted.

Gates, Thomas S.↗
NASA NTRS1995

Time-Dependent Behavior of a Graphite/Thermoplastic Composite and the Effects of Stress and Physical Aging

Experimental studies were performed to determine the effects of stress and physical aging on the matrix dominated time dependent properties of IM7/8320 composite. Isothermal tensile creep/aging test techniques developed for polymers were adapted for testing of the composite material. Time dependent transverse and shear compliance's for an orthotropic plate were found from short term creep compliance measurements at constant, sub-T(8) temperatures. These compliance terms were shown to be affected by physical aging. Aging time shift factors and shift rates were found to be a function of temperature and applied stress.

Gates, Thomas S.↗
NASA NTRS2012

Hybrid Wing-Body (HWB) Pressurized Fuselage Modeling, Analysis, and Design for Weight Reduction

This paper describes the interim progress for an in-house study that is directed toward innovative structural analysis and design of next-generation advanced aircraft concepts, such as the Hybrid Wing-Body (HWB) and the Advanced Mobility Concept-X flight vehicles, for structural weight reduction and associated performance enhancement. Unlike the conventional, skin-stringer-frame construction for a cylindrical fuselage, the box-type pressurized fuselage panels in the HWB undergo significant deformation of the outer aerodynamic surfaces, which must be minimized without significant structural weight penalty. Simple beam and orthotropic plate theory is first considered for sizing, analytical verification, and possible equivalent-plate analysis with appropriate simplification. By designing advanced composite stiffened-shell configurations, significant weight reduction may be possible compared with the sandwich and ribbed-shell structural concepts that have been studied previously. The study involves independent analysis of the advanced composite structural concepts that are presently being developed by The Boeing Company for pressurized HWB flight vehicles. High-fidelity parametric finite-element models of test coupons, panels, and multibay fuselage sections, were developed for conducting design studies and identifying critical areas of potential failure. Interim results are discussed to assess the overall weight/strength advantages.

Mukhopadhyay, Vivek↗
NASA NTRS2013

Hybrid Wing-Body Pressurized Fuselage and Bulkhead, Design and Optimization

The structural weight reduction of a pressurized Hybrid Wing-Body (HWB) fuselage is a serious challenge. Hence, research and development are presently being continued at NASA under the Environmentally Responsible Aviation (ERA) and Subsonic Fixed Wing (SFW) projects in collaboration with the Boeing Company, Huntington Beach and Air Force Research Laboratory (AFRL). In this paper, a structural analysis of the HWB fuselage and bulkhead panels is presented, with the objectives of design improvement and structural weight reduction. First, orthotropic plate theories for sizing, and equivalent plate analysis with appropriate simplification are considered. Then parametric finite-element analysis of a fuselage section and bulkhead are conducted using advanced stitched composite structural concepts, which are presently being developed at Boeing for pressurized HWB flight vehicles. With this advanced stiffened-shell design, structural weights are computed and compared to the thick sandwich, vaulted-ribbed-shell, and multi-bubble stiffened-shell structural concepts that had been studied previously. The analytical and numerical results are discussed to assess the overall weight/strength advantages.

Mukhopadhyay, Vivek↗
NASA NTRS1972

Stability of orthotropic stiffened composite plates.

It is pointed out that the buckling problem of a plate with restrictions resulting from boundary conditions is suited for an application of Lagrangian multipliers. An approach used by Budiansky and Hu (1946) is extended to the study of orthotropic stiffened plates. The variations of the total energy with respect to the three deformation components are considered. The equilibrium equations and the boundary conditions are obtained. It is shown that the deflection functions must satisfy the equilibrium equations. The Lagrangian multipliers are then used to solve stability problems on the basis of the total energy involved, the equilibrium equations, and the boundary conditions. The theoretical analysis is supplemented by an experimental investigation.

Chiu, K. D.↗
NASA NTRS1972

Elastostatic stress analysis of orthotropic rectangular center-cracked plates

A mapping-collocation method was developed for the elastostatic stress analysis of finite, anisotropic plates with centrally located traction-free cracks. The method essentially consists of mapping the crack into the unit circle and satisfying the crack boundary conditions exactly with the help of Muskhelishvili's function extension concept. The conditions on the outer boundary are satisfied approximately by applying the method of least-squares boundary collocation. A parametric study of finite-plate stress intensity factors, employing this mapping-collocation method, is presented. It shows the effects of varying material properties, orientation angle, and crack-length-to-plate-width and plate-height-to-plate-width ratios for rectangular orthotropic plates under constant tensile and shear loads.

Gyekenyesi, G. S.↗
NASA NTRS1985

Stability and vibration of isotropic, orthotropic and laminated plates according to a higher-order shear deformation theory

A higher-order shear deformation theory is used to demonstrate the natural frequencies and buckling loads of elastic plates. The theory accounts for parabolic distribution of the transverse shear strains through the thickness of the plate and rotary inertia. Exact solutions of simply supported plates are obtained and the results are compared with the exact solutions of three-dimensional elasticity theory, the first-order shear deformation theory, and the classical plate theory. The present theory predicts the frequencies and buckling loads more accurately when compared to the first-order and classical plate theories.

Reddy, J. N.↗
NASA NTRS1979

Optimum design of laminated plates under shear

This paper is concerned with the optimum design of plates with orthotropic layers under shear. The plates considered are the laminates of N orthotropic layers whose principal material axes coincide with the plate axes. Each layer is assumed to have the same thickness and an equal number of fibers in the direction of + alpha sub i and - alpha sub i with respect to the plate axis. The fiber directions which give the highest shear buckling stress are found by utilizing a mathematical optimization technique.

Hirano, Y.↗