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NASA NTRS1976

A finite-element analysis of fatigue crack closure

The paper is concerned with the application of a two-dimensional, nonlinear, finite-element analysis using an incremental theory of plasticity to predict crack-closure and crack-opening stresses during the crack-growth process under cyclic loading. A two-dimensional finite-element computer program is developed, which accounts for both elastic-plastic material behavior and changing boundary conditions associated with crack extension and intermittent contact of the crack surfaces under cyclic loading. An efficient technique to account for changing boundary conditions under cyclic loading is also incorporated into the nonlinear analysis program. This program is used to study crack extension and crack closure behavior in a center-cracked panel under constant-amplitude and two-level block loading. The calculated crack-opening stresses are found to be quantitatively consistent with experimental measurements.

Newman, J. C., Jr.↗

NASA NTRS1991

Incorporating finite element analysis into component life and reliability

A method for calculating a component's design survivability by incorporating finite element analysis and probabilistic material properties was developed. The method evaluates design parameters through direct comparisons of component survivability expressed in terms of Weibull parameters. The analysis was applied to a rotating disk with mounting bolt holes. The highest probability of failure occurred at, or near, the maximum shear stress region of the bolt holes. Distribution of failure as a function of Weibull slope affects the probability of survival. Where Weibull parameters are unknown for a rotating disk, it may be permissible to assume Weibull parameters, as well as the stress-life exponent, in order to determine the disk speed where the probability of survival is highest.

August, Richard↗

NASA NTRS1986

Finite element analysis of steady and transiently moving/rolling nonlinear viscoelastic structure. Part 1: Theory

In a three part series of papers, a generalized finite element analysis scheme is developed to handle the steady and transient response of moving/rolling nonlinear viscoelastic structure. This paper considers the development of the moving/rolling element strategy, including the effects of large deformation kinematics and viscoelasticity modelled by fractional integro-differential operators. To improve the solution strategy, a special hierarchical constraint procedure is developed for the case of steady rolling/translating as well as a transient scheme involving the use of a Grunwaldian representation of the fractional operator. In the second and third parts of the paper, 3-D extensions are developed along with transient contact strategies enabling the handling of impacts with obstructions. Overall, the various developments are benchmarked via comprehensive 2- and 3-D simulations. These are correlated with experimental data to define modelling capabilities.

Padovan, Joe↗

NASA NTRS1987

Finite element analysis of steady and transiently moving/rolling nonlinear viscoelastic structure. I - Theory

In a three-part series of papers, a generalized finite element analysis scheme is developed to handle the steady and transient response of moving/rolling nonlinear viscoelastic structure. This paper considers the development of the moving/rolling element strategy, including the effects of large deformation kinematics and viscoelasticity modeled by fractional integrodifferential operators. To improve the solution strategy, a special hierarchical constraint procedure is developed for the case of steady rolling/translating, as well as a transient scheme involving the use of a Grunwaldian representation of the fractional operator.

Padovan, Joe↗

NASA NTRS1982

Chemorheology of reactive systems: Finite element analysis

The equations which govern the nonisothermal flow of reactive fluids are outlined, and the means by which finite element analysis is used to solve these equations for the sort of arbitrary boundary conditions encountered in industrial practice are described. The performance of the computer code is illustrated by several trial problems, selected more for their value in providing insight to polymer processing flows than as practical production problems. Although a good deal remains to be learned as to the performance and proper use of this numerical technique, it is undeniably useful in providing better understanding of today's complicated polymer processing problems.

Douglas, C.↗

NASA NTRS1990

2-D to 3-D global/local finite element analysis of cross-ply composite laminates

An example of two-dimensional to three-dimensional global/local finite element analysis of a laminated composite plate with a hole is presented. The 'zoom' technique of global/local analysis is used, where displacements of the global/local interface from the two-dimensional global model are applied to the edges of the three-dimensional local model. Three different hole diameters, one, three, and six inches, are considered in order to compare the effect of hole size on the three-dimensional stress state around the hole. In addition, three different stacking sequences are analyzed for the six inch hole case in order to study the effect of stacking sequence. The existence of a 'critical' hole size, where the interlaminar stresses are maximum, is indicated. Dispersion of plies at the same angle, as opposed to clustering, is found to reduce the magnitude of some interlaminar stress components and increase others.

Thompson, D. Muheim↗

NASA NTRS1989

A locally implicit finite element analysis algorithm for 3-D compressible flows

The paper outlines the research results on the development of a finite-element analysis procedure for three-dimensional compressible viscous flows. Some new algorithmic features of the computational model, such as a locally implicit solution scheme which avoids the necessity of computation and assembly of global matrices. The new algorithm makes it applicable to large-scale three-dimensional flow problems of practical interest, for example, the analysis of flows in Space Shuttle Main Engine (SSME).

Reddy, K. C.↗

NASA NTRS1993

Elastic-plastic mixed-iterative finite element analysis: Implementation and performance assessment

An elastic-plastic algorithm based on Von Mises and associative flow criteria is implemented in MHOST-a mixed iterative finite element analysis computer program developed by NASA Lewis Research Center. The performance of the resulting elastic-plastic mixed-iterative analysis is examined through a set of convergence studies. Membrane and bending behaviors of 4-node quadrilateral shell finite elements are tested for elastic-plastic performance. Generally, the membrane results are excellent, indicating the implementation of elastic-plastic mixed-iterative analysis is appropriate.

Sutjahjo, Edhi↗

NASA NTRS1985

Simplex finite element analysis of viscous incompressible flow with penalty function formulation

Viscous flow calculations are important for the determination of separated flows, recirculating flows, secondary flows and so on. This paper presents a penalty function approach for the finite element analysis of steady incompressible viscous flow. A simplex element is used with linear velocity and constant pressure in contrast to other works which usually employ higher order elements. Simplex elements yield analytical expressions for the element matrices which in turn lead to efficient solutions. Earlier works have partially indicated how constraint and lock-up problems might be avoided for simplex elements. This paper extends the earlier works by indicating the approach in detail and verifying that it is successful for several applications not discussed in the literature so far. Solution times and accuracy considerations are discussed for Couette flow, plane Poiseuille flow, a driven cavity problem, and laminar and turbulent flow over a step.

Allaire, P. E.↗

NASA NTRS1972

Californium-252 neutron capture and decay methods for elemental analysis

The feasibility of using a Cf-252 neutron source in conjunction with a capture and/or decay gamma ray method for elemental analysis on lunar or planetary missions was tested. The general problems of using a Cf-252 neutron source for both decay and capture gamma ray analysis in terrestrial environments included the determination of the capture gamma ray spectra by neutron absorption in various metals used for the space hardware, Cf-252 source encapsulation materials, shielding, geometry, and optimum source size for a space mission. Computer data reduction and data transmission techniques were also investigated.

Source record↗

NASA NTRS1992

Composite Stiffened Panels: Part I - Stiffness, Thermal Expansion, and Thermal Bending Formulation for Finite Element Analysis

A method is presented for formulating stiffness terms and thermal coefficients of fiber-reinforced composite, stiffened panels for input to finite element analysis (FEA). The method is robust enough to handle panels with general cross sectional shapes, including those which are unsymmetric and/or unbalanced. New thermal coefficients are introduced to quantify panel response from through-the-thickness temperature gradients. Equations are defined for stiffness, thermal expansion, and thermal bending that consider the full complement of membrane, bending, membrane-bending coupling, and transverse shear behavior. A technique of implementing this capability with a single plane of shell finite elements using the MSC/NASTRAN(TradeMark) FEA program is revealed. Finally, an example of a composite, hat-stiffened panel is included to demonstrate errors that occur when an unsymmetric panel is symmetrically formulated as traditionally done. These erroneous values and the correct ones produced from the presented method are listed for the panel's stiffness matrices, thermal expansion and bending vectors, and the forces and moments that are thermally induced from in-plane and through-the-thickness temperature gradients.

Craig S Collier↗

NASA NTRS1981

Finite element analysis of instability-related delamination growth

A parametric study of postbuckled through-width delaminations in laminated coupons was performed. A finite element analysis was developed to analyze the coupons as a combination of linear and geometrically nonlinear components. Because most of the coupon configuration studied behaves linearly, the mixed linear and nonlinear analysis greatly reduced computational costs. The analysis was verified by comparing numerical with exact solutions for simple hypothetical problems. In addition, measured lateral deflections of postbuckled through-width delaminations in laminated coupons were compared with predicted deflections. In the parametric study, stress distributions and strain-energy release rates were calculated for various delamination lengths, delamination depths, applied loads, and lateral deflections. Also, a small number of coupons with through-width delaminations were fatigue tested to obtain delamination growth data. Calculated strain-energy release rates were compared with the observed growth rates to determine the relative importance of the Mode 1 and Mode 2 components of energy release. Growth process was dominated by G sub I.

Whitcomb, J. D.↗

NASA NTRS1993

TransFit: Finite element analysis data fitting software

The Advanced X-Ray Astrophysics Facility (AXAF) mission support team has made extensive use of geometric ray tracing to analyze the performance of AXAF developmental and flight optics. One important aspect of this performance modeling is the incorporation of finite element analysis (FEA) data into the surface deformations of the optical elements. TransFit is software designed for the fitting of FEA data of Wolter I optical surface distortions with a continuous surface description which can then be used by SAO's analytic ray tracing software, currently OSAC (Optical Surface Analysis Code). The improved capabilities of Transfit over previous methods include bicubic spline fitting of FEA data to accommodate higher spatial frequency distortions, fitted data visualization for assessing the quality of fit, the ability to accommodate input data from three FEA codes plus other standard formats, and options for alignment of the model coordinate system with the ray trace coordinate system. TransFit uses the AnswerGarden graphical user interface (GUI) to edit input parameters and then access routines written in PV-WAVE, C, and FORTRAN to allow the user to interactively create, evaluate, and modify the fit. The topics covered include an introduction to TransFit: requirements, designs philosophy, and implementation; design specifics: modules, parameters, fitting algorithms, and data displays; a procedural example; verification of performance; future work; and appendices on online help and ray trace results of the verification section.

Freeman, Mark↗

NASA NTRS1982

Finite-element analysis of initiation, stable crack growth and instability using a crack-tip-opening displacement criterion

An elastic-plastic (incremental and small strain) finite element analysis was used with a crack growth criterion to study crack initiation, stable crack growth, and instability under monotonic loading to failure of metallic materials. The crack growth criterion was a critical crack-tip-opening displacement (CTOD) at a specified distance from the crack tip, or equivalently, a critical crack-tip-opening angle (CTOA). Whenever the CTOD (or CTOA) equaled or exceeded a critical value, the crack was assumed to grow. Single values of critical CTOD were used in the analysis to model crack initiation, stable crack growth, and instability for 7075-T651 and 2024-T351 aluminum alloy compact specimens. Calculated and experimentally measured CTOD values at initiation agreed well for both aluminum alloys. These critical CTOD values were also used to predict failure loads on center-crack tension specimens and a specially-designed three-hole-crack tension specimen made of the two aluminum alloys and of 304 stainless steel. All specimens were 12.7 mm thick. Predicted failure loads for 7075-T651 aluminum alloy and 304 stainless steel specimens were generally within + or - 15 percent of experimental failure loads, whereas the predicted failure loads for 2024-T351 aluminum alloy specimens were generally within + or - 5 percent of the experimental loads.

Newman, J. C., Jr.↗

NASA NTRS2016

Finite Element Analysis and Test Results Comparison for the Hybrid Wing Body Center Section Test Article

This report documents the comparison of test measurements and predictive finite element analysis results for a hybrid wing body center section test article. The testing and analysis efforts were part of the Airframe Technology subproject within the NASA Environmentally Responsible Aviation project. Test results include full field displacement measurements obtained from digital image correlation systems and discrete strain measurements obtained using both unidirectional and rosette resistive gauges. Most significant results are presented for the critical five load cases exercised during the test. Final test to failure after inflicting severe damage to the test article is also documented. Overall, good comparison between predicted and actual behavior of the test article is found.

Przekop, Adam↗

NASA NTRS1988

An elastic-plastic finite-element analysis of the J-resistance curve using a CTOD criterion

The fracture process in compact and bend specimens was simulated using a two-dimensional finite-element analysis of the J-resistance (J-R) curve and a CTOD criterion. The J-R curves were calculated from the numerical results for each specimen type using several different methods. In general, the J-R curves obtained for the bend specimens were found to be higher than those for the compact specimens, especially beyond maximum load. However, below the maximum load, the modified deformation theory of plasticity and the contour-integral J(r) method resulted in very similar J-R curves for both specimen types.

Newman, J. C., Jr.↗

NASA NTRS1980

Integrated thermal-structural finite element analysis

An integrated thermal-structural finite element approach for efficient coupling of thermal and structural analysis is presented. An integrated thermal-structural rod element is developed and used in four thermal-structural applications; the accuracy of this integrated approach is illustrated by comparisons with the customary approach of finite difference thermal-finite element structural analyses. Results show that integrated thermal-structural analysis of structures modeled with rod elements is more accurate than conventional analysis, and that its further development promises significant results.

Thornton, E. A.↗

NASA NTRS1972

Progress in nonlinear finite element analysis using asymptotic solution techniques.

The existence of standard forms of finite element equations for nonlinear analysis is observed. These are noted to provide a sufficiently special circumstance to admit the construction of asymptotic solution techniques. Although efforts in this direction have been made only recently, a number of distinct approaches to asymptotic solution techniques for finite element analysis have been put forward and are examined herein. Consideration is given to the differences and similarities of the approaches and the resulting methods of solution. Special characteristics regarding applicability, accuracy and efficiency are delineated.

Mallett, R. H.↗