SEARCH · Search NASA

Results for “Elastic Shape Analysis”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5

All sources NASA NTRS DOE OSTI

NASA NTRS2006

HFGMC Enhancement of MAC/GMC

Additional information about a mathematical model denoted the high-fidelity generalized method of cells (HFGMC) and implementation of the HFGMC within version 4.0 of the MAC/GMC software has become available. MAC/GMC (Micromechanics Analysis Code With Generalized Method of Cells) was a topic of several prior NASA Tech Briefs articles, version 4.0 having been described in "Comprehensive Micromechanics-Analysis Code - Version 4.0" (LEW-17495-1), NASA Tech Briefs, Vol. 29, No. 9 (September 2005), page 54. MAC/GMC predicts elastic and inelastic thermomechanical responses of composite materials. MAC/GMC utilizes the generalized method of cells (GMC) - a model of micromechanics that predicts macroscopic responses of a composite material as functions of the properties, sizes, shapes, and responses of its constituents (e.g., matrix and fibers). The accuracy of the GMC is limited by neglect of coupling between normal and shear stresses. The HFGMC was developed by combining elements of the GMC and a related model, denoted the higher-order theory for functionally graded materials (HOTFGM), that can account for this coupling. Hence, the HFGMC enables simulation of stress and strain with greater accuracy. Some alterations of the MAC/GMC data structure were necessitated by the greater computational complexity of the HFGMC.

Arnold, Steven M.↗

NASA NTRS2005

Stress Analysis of Composite Cylindrical Shells With an Elliptical Cutout

A special-purpose, semi-analytical solution method for determining the stress and deformation fields in a thin laminated-composite cylindrical shell with an elliptical cutout is presented. The analysis includes the effects of cutout size, shape, and orientation; nonuniform wall thickness; oval-cross-section eccentricity; and loading conditions. The loading conditions include uniform tension, uniform torsion, and pure bending. The analysis approach is based on the principle of stationary potential energy and uses Lagrange multipliers to relax the kinematic admissibility requirements on the displacement representations through the use of idealized elastic edge restraints. Specifying appropriate stiffness values for the elastic extensional and rotational edge restraints (springs) allows the imposition of the kinematic boundary conditions in an indirect manner, which enables the use of a broader set of functions for representing the displacement fields. Selected results of parametric studies are presented for several geometric parameters that demonstrate that analysis approach is a powerful means for developing design criteria for laminated-composite shells.

Nemeth, M. P.↗

NASA NTRS2018

Simulation of Stochastic Mud-Crack Damage Formation in an Environmental Barrier Coating

The integrated Finite Element Analysis–Micromechanics Analysis Code/Ceramics Analysis and Reliability Evaluation of Structures (FEAMAC/CARES) program was used to simulate the formation of mudflat-cracks from thermomechanical loading on a multi-layered Environmental Barrier Coating (EBC) system deposited on a ceramic substrate. FEAMAC/CARES combines MAC/GMC multiscale composite micromechanics code with CARES/Life probabilistic multiaxial failure criteria code and Abaqusfinite element analysis. In this work, step function elastic modulus reduction of randomly damaged finite elements was used to represent discrete cracking events. The use of many small-sized low-aspect-ratio finite elements enabled the depiction of crack boundaries and formation of mudflat patterned damage. Demonstrated examples include finite element models of button–sized disk–shaped 3-D specimen, and a 2-D model of through-the-thickness cross-section. All models were subjected to a progressive cool down from 1300oC to room temperature. Mudflat crack damage in the coating system resulted from the buildup of residual tensile stresses between the individual material constituents from thermal expansion mismatch. A 2-parameter Weibull distribution characterized the coating layer stochastic strength response and the effect of the Weibull modulus on the formation of damage was studied here.

residual tensile stress↗

NASA NTRS1973

Three-dimensional elastic stress and displacement analysis of finite circular geometry solids containing cracks

A seminumerical method is presented for solving a set of coupled partial differential equations subject to mixed and coupled boundary conditions. The use of this method is illustrated by obtaining solutions for two circular geometry and mixed boundary value problems in three-dimensional elasticity. Stress and displacement distributions are calculated in an axisymmetric, circular bar of finite dimensions containing a penny-shaped crack. Approximate results for an annular plate containing internal surface cracks are also presented.

Gyekenyesi, J. P.↗

NASA NTRS1975

Vanishing rainbows near orbiting and the energy dependence of rainbow scattering - Relation to properties of the potential

The energy threshold behavior of elastic rainbow scattering near the transition to orbiting is derived. Analysis of the energy dependence of the rainbow angle shows that the full range from high energies down to orbiting can be fitted with two parameters. Thus, measurements of the rainbow angle can give essentially only two pieces of information about the potential. For potentials of common shapes, such measurements are sensitive to regions of the potential just beyond the minimum and give information about the shape of the potential in this range. However, neither a minimum nor a point of inflection in the potential is necessary for rainbow scattering.

Greene, E. F.↗

NASA NTRS1988

Accuracy problems associated with semi-analytical derivatives of static response

The semianalytical method is widely used for calculating derivatives of static response with respect to design variables for structures modeled by finite elements. This paper shows that the method can have serious accuracy problems for shape design variables in structures modeled by beam elements. The problem was first discovered in the analysis of a complex car model which is described. Next, it is shown that the same accuracy problem occurs for the simplest beam structures. Finally, the problem is shown to be associated with a high ratio of rigid body rotation to elastic deformation, and a test is developed to diagnose the severity of the problem in a given structure. Several examples are presented to show the validity of this test.

Barthelemy, Bruno↗

NASA NTRS1995

Modeling and characterization of through-the-thickness properties of 3D woven composites

The through-the-thickness properties of three-dimensionally (3D) woven carbon/epoxy composites have been studied. The investigation aimed at the evaluation and development of test methodologies for the property characterization in the thickness direction, and the establishment of fiber architectures were studied: layer-to-layer Angle Interlock, through-the-thickness Orthogonal woven preform with surface pile was also designed and manufactured for the fabrication of tensile test coupons with integrated grips. All the preforms were infiltrated by the resin transfer molding technique. The microstructures of the composites were characterized along the warp and fill (weft) directions to determine the degree of yarn undulations, yarn cross-sectional shapes, and microstructural dimensions. These parameters were correlated to the fiber architecture. Specimens were designed and tested for the direct measurement of the through-the-thickness tensile, compressive and shear properties of the composites. Design optimization was conducted through the analysis of the stress fields within the specimen coupled with experimental verification. The experimentally-derived elastic properties in the thickness direction compared well with analytical predictions obtained from a volume averaging model.

Hartranft, Dru↗

NASA NTRS1979

Influence of interface on composite failure

The influence of the interface on the composite system behavior is investigated by analytical modeling. The stress analysis is based on the two-dimensional finite element procedure in which twelve-node isoparametric elements with cubic shape functions are used. The location of possible failure sites is predicted by the strain energy density (SED) failure theory which assumes failure to coincide with locations of minimum SED while the locations of maximum SED correspond to regions of excessive distortion or yielding. The results of the analysis show that the way in which the modulus of elasticity varies within the interface is as important in modeling as the average interface modulus.

Sih, G. C.↗

NASA NTRS2007

Stress Analysis of Composite Cylindrical Shells with an Elliptical Cutout

A special-purpose, semi-analytical solution method for determining the stress and deformation fields in a thin laminated-composite cylindrical shell with an elliptical cutout is presented. The analysis includes the effects of cutout size, shape, and orientation; non-uniform wall thickness; oval-cross-section eccentricity; and loading conditions. The loading conditions include uniform tension, uniform torsion, and pure bending. The analysis approach is based on the principle of stationary potential energy and uses Lagrange multipliers to relax the kinematic admissibility requirements on the displacement representations through the use of idealized elastic edge restraints. Specifying appropriate stiffness values for the elastic extensional and rotational edge restraints (springs) allows the imposition of the kinematic boundary conditions in an indirect manner, which enables the use of a broader set of functions for representing the displacement fields. Selected results of parametric studies are presented for several geometric parameters that demonstrate that analysis approach is a powerful means for developing design criteria for laminated-composite shells.

Oterkus, E.↗

NASA NTRS2018

Weibull-Based Stochastic Simulation of Mud-Crack Damage Formation in an Environmental Barrier Coating

The integrated Finite Element Analysis Micromechanics Analysis Code/Ceramics Analysis and Reliability Evaluation of Structures (FEAMAC/CARES) program was used to simulate the formation of mudflat-cracks from thermomechanical loading on a multi-layered Environmental Barrier Coating (EBC) system deposited on a ceramic substrate. FEAMAC/CARES combines MAC/GMC (Micromechanics Analysis Code/Generalized Method of Cells) multiscale composite micromechanics code with CARES/Life probabilistic multiaxial failure criteria code and Abaqusfinite element analysis. In this work, step function elastic modulus reduction of randomly damaged finite elements was used to represent discrete cracking events. The use of many small-sized low-aspect-ratio finite elements enabled the depiction of crack boundaries and formation of mudflat patterned damage. Demonstrated examples include finite element models of button-sized disk-shaped 3-D specimen, and a 2-D model of through-the-thickness cross-section. All models were subjected to a progressive cool down from 1300 degrees Centigrade to room temperature. Mudflat crack damage in the coating system resulted from the buildup of residual tensile stresses between the individual material constituents from thermal expansion mismatch. A 2-parameter Weibull distribution characterized the coating layer stochastic strength response and the effect of the Weibull modulus on the formation of damage was studied here.

Residual Tensile Stress↗

NASA NTRS1984

Development of selected advanced aerodynamics and active control concepts for commercial transport aircraft

Work done under the Energy Efficient Transport project in the field of advanced aerodynamics and active controls is summarized. The project task selections focused on the following: the investigation of long-duct nacelle shape variation on interference drag; the investigation of the adequacy of a simple control law for the elastic modes of a wing; the development of the aerodynamic technology at cruise and low speed of high-aspect-ratio supercritical wings of high performance; and the development of winglets for a second-generation jet transport. All the tasks involved analysis and substantial wind tunnel testing. The winglet program also included flight evaluation. It is considered that the technology base has been built for the application of high-aspect-ratio supercritical wings and for the use of winglets on second-generation transports.

Taylor, A. B.↗

NASA NTRS1971

Gravity flow of powder in a lunar environment. Part 2: Analysis of flow initiation

A small displacement-small strain finite element technique utilizing the constant strain triangle and incremental constitutive equations for elasticplastic (media nonhardening and obeying a Coulomb yield condition) was applied to the analysis of gravity flow initiation. This was done in a V-shaped hopper containing a powder under lunar environmental conditions. Three methods of loading were examined. Of the three, the method of computing the initial state of stress in a filled hopper prior to drawdown, by adding material to the hopper layer by layer, was the best. Results of the analysis of a typical hopper problem show that the initial state of stress, the elastic moduli, and the strength parameters have an important influence on material response subsequent to the opening of the hopper outlet.

Pariseau, W. G.↗

NASA NTRS1975

Application of NASTRAN for stress analysis of left ventricle of the heart

Knowing the stress and strain distributions in the left ventricular wall of the heart is a prerequisite for the determination of the muscle elasticity and contractility in the process of assessing the functional status of the heart. NASTRAN was applied for the calculation of these stresses and strains and to help in verifying the results obtained by the computer program FEAMPS which was specifically designed for the plane-strain finite-element analysis of the left ventricular cross sections. Adopted for the analysis are the true shape and dimensions of the cross sections reconstructed from multiplanar X-ray views of a left ventricle which was surgically isolated from a dog's heart but metabolically supported to sustain its beating. A preprocessor was prepared to accommodate both FEAMPS and NASTRAN, and it has also facilitated the application of both the triangular element and isoparameteric quadrilateral element versions of NASTRAN. The stresses in several crucial regions of the left ventricular wall calculated by these two independently developed computer programs are found to be in good agreement. Such confirmation of the results is essential in the development of a method which assesses the heart performance.

Pao, Y. C.↗

NASA NTRS1976

Stability of elastic bending and torsion of uniform cantilever rotor blades in hover with variable structural coupling

The stability of elastic flap bending, lead-lag bending, and torsion of uniform, untwisted, cantilever rotor blades without chordwise offsets between the elastic, mass, tension, and areodynamic center axes is investigated for the hovering flight condition. The equations of motion are obtained by simplifying the general, nonlinear, partial differential equations of motion of an elastic rotating cantilever blade. The equations are adapted for a linearized stability analysis in the hovering flight condition by prescribing aerodynamic forces, applying Galerkin's method, and linearizing the resulting ordinary differential equations about the equilibrium operating condition. The aerodynamic forces are obtained from strip theory based on a quasi-steady approximation of two-dimensional unsteady airfoil theory. Six coupled mode shapes, calculated from free vibration about the equilibrium operating condition, are used in the linearized stability analysis. The study emphasizes the effects of two types of structural coupling that strongly influence the stability of hingeless rotor blades. The first structural coupling is the linear coupling between flap and lead-lag bending of the rotor blade. The second structural coupling is a nonlinear coupling between flap bending, lead-lag bending, and torsion deflections. Results are obtained for a wide variety of hingeless rotor configurations and operating conditions in order to provide a reasonably complete picture of hingeless rotor blade stability characteristics.

Hodges, D. H., Roberta.↗

NASA NTRS1999

Aeroelastic Analysis of a Trimmed Generic Hypersonic Vehicle

The aeroelastic equations of motion governing a hypersonic vehicle in free flight are derived. The equations of motion for a translating and rotating flexible body using Lagrange's equations in terms of quasi-coordinates are presented. These equations are simplified for the case of a vehicle with pitch and plunge rigid body degrees of freedom and small elastic displacements. The displacements are approximated by a truncated series of the unrestrained mode shapes, which are obtained using equivalent plate theory. Subsequently, the nonlinear equations of motion are linearized about the trim state, which is obtained using a rigid body trim model and steady hypersonic aerodynamics. The appropriate flutter derivatives are calculated from piston theory. Results describing mode shapes, trim behavior, and aeroelastic stability of a generic hypersonic vehicle are presented.

Nydick, I.↗

NASA NTRS2011

Effect of Graphene Addition on Shape Memory Behavior of Epoxy Resins

Shape memory polymers (SMPs) and composites are a special class of smart materials known for their ability to change size and shape upon exposure to an external stimulus (e.g. light, heat, pH, or magnetic field). These materials are commonly used for biomedical applications; however, recent attempts have been made towards developing SMPs and composites for use in aircraft and space applications. Implementing SMPs and composites to create a shape change effect in some aircraft structures could potentially reduce drag, decrease fuel consumption, and improve engine performance. This paper discusses the development of suitable materials to use in morphing aircraft structures. Thermally responsive epoxy SMPs and nanocomposites were developed and the shape memory behavior and thermo-mechanical properties were studied. Overall, preliminary results from dynamic mechanical analysis (DMA) showed that thermally actuated shape memory epoxies and nanocomposites possessed Tgs near approximately 168 C. When graphene nanofiller was added, the storage modulus and crosslinking density decreased. On the other hand, the addition of graphene enhanced the recovery behavior of the shape memory nanocomposites. It was assumed that the addition of graphene improved shape memory recovery by reducing the crosslinking density and increasing the elasticity of the nanocomposites.

Williams, Tiffany↗

NASA NTRS1990

Delamination Analysis Of Composite Curved Bars

Classical anisotropic elasticity theory used to construct "multilayer" composite semicircular curved bar subjected to end forces and end moments. Radial location and intensity of open-mode delamination stress calculated and compared with results obtained from anisotropic continuum theory and from finite element method. Multilayer theory gave more accurate predictions of location and intensity of open-mode delamination stress. Currently being applied to predict open-mode delamination stress concentrations in horse-shoe-shaped composite test coupons.

Ko, William L.↗

NASA NTRS2001

Rheology of Foam Near the Order-Disorder Transition

The first part of our research results are summarized in the recent journal publication: J. Gregory McDaniel and R. Glynn Holt, 'Measurement of aqueous foam rheology by acoustic levitation', Phys. Rev. E 61, 2204 (2000). This aspect of the work was a combination of experiment and analysis. We built a levitation system capable of acoustically levitating small samples of aqueous foam of arbitrary gas and liquid volume fractions. We then modulated the acoustic field to induce normal mode oscillations of the foam samples. The observables from the experiment were frequency and mode number. For dry (roughly > 70% gas by volume) foams and small deformations, we developed an effective medium, normal-modes analysis which took the frequency and mode number from experiment, and gave us the shear elastic modulus of the foam as a function of Poisson's ratio. The second part of our results may be found in a soon-to-be submitted manuscript 'Dynamics of aqueous foam drops', I.Sh. Akhatov, J.G. McDaniel and R.G. Holt, describing our modeling in the wet foam limit by considering the acoustic problem. This aspect of the research is purely theoretical. Beginning from a mass-conserving mixture law, the fully nonlinear equations of motion for a wet (roughly < 10% gas by volume) foam drop of initially spherical shape were derived. The frequencies for normal mode oscillations were derived in the linear inviscid limit. The nonlinear equations were numerically solved to elicit the motion of a foam drop under acoustic excitation. The role of the time-varying void fraction in breathing-mode oscillations is of particular interest. As of the end of the current (NAG#3-2121) grant, this work was not yet concluded. We continue to work on this aspect in order to extend the analysis to cover the transition regime of gas volume fractions, as well as to compare to experiments in the wet regime.

Holt, R. Glynn↗