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  • Other Sources  (175)
  • STRUCTURAL MECHANICS  (175)
  • 1980-1984  (175)
  • 1981  (175)
  • 1
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    Practical implementation of the double linear damage rule and damage curve approach for treating cumulative fatigue damage (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Simple procedures are given for treating cumulative fatigue damage under complex loading history using either the damage curve concept or the double linear damage rule. A single equation is given for use with the damage curve approach; each loading event providing a fraction of damage until failure is presumed to occur when the damage sum becomes unity. For the double linear damage rule, analytical expressions are given for determining the two phases of life. The procedure comprises two steps, each similar to the conventional application of the commonly used linear damage rule. Once the sum of cycle ratios based on Phase I lives reaches unity, Phase I is presumed complete, and further loadings are summed as cycle ratios based on Phase II lives. When the Phase II sum attains unity, failure is presumed to occur. It is noted that no physical properties or material constants other than those normally used in a conventional linear damage rule analysis are required for application of either of the two cumulative damage methods described. Illustrations and comparisons are discussed for both methods.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 17; Apr. 198
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  • 2
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    Surface phenomena in elasticity (1981)
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    Publication Date: 2011-08-18
    Description: Problems of elasticity associated with the behavior of free surfaces of elastic bodies are reviewed with particular reference to the propagation of characteristic waves and the criteria of wrinkling of free surfaces. All transformations are given for the case when a free surface of an elastic body is streamlined by the flow of inviscid fluid. The wrinkling phenomenon is illustrated by example.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Elasticity; 11; Apr. 198
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  • 3
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    Reliability-based optimization under random vibration environment (1981)
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    Publication Date: 2011-08-18
    Description: A methodology of formulating the optimum design problem for structural systems with random parameters and subjected to random vibration as a mathematical programming problem is presented. The proposed method is applied to the optimum design of a cantilever beam with a tip mass and a truss structure supporting a water tank. The excitations are assumed to be Gaussian processes and the geometric and material properties are taken to be normally distributed random variables. The probabilistic constraints are specified for individual failure modes since it is easier to specify the reliability level for each failure mode keeping in view the consequences of failure in that particular mode. The time parameter appearing in the random vibration based constraints is eliminated by replacing the probabilities of failure by suitable upper bounds. The numerical results demonstrate the feasibility and effectiveness of applying the reliability-based design concepts to structures with random parameters and operating in random vibration environment.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 14; 5-6,; 1981
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  • 4
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    SPAR analysis of LDEF vibration characteristics (1981)
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    Publication Date: 2011-08-18
    Description: This paper presents a structural dynamic modeling of the Long Duration Exposure Facility (LDEF), which is a Space Shuttle payload of passive scientific experiments contained in trays mounted on a large cylindrically shaped structure. Special detailed finite element modeling, using the SPAR system of computer programs was required to obtain good agreement between analytical and test vibrations modes. Experimental trays contributed significantly to overall LDEF stiffnesses, and these contributions were realistically represented for each tray by the stiffness matrix of an equivalent orthotropic panel in the overall LDEF SPAR model. Orthotropic stiffnesses for this panel were obtained from finely detailed statically loaded tray SPAR models in which stiffness coupling was accounted for along with partial relative sliding allowed by the tray clamping attachments. Joint boundary conditions were also significant in the structural dynamic modeling of LDEF, and static data proved valuable in assessing modeling of local end fittings.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 13; Aug. 198
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  • 5
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    Existence of axisymmetric modes of thin cylindrical shells with axial displacement restraint (1981)
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    Publication Date: 2011-08-18
    Description: A necessary and sufficient condition is derived for the existence of the axisymmetric mode of cylindrical shells with a radial displacement having one half wave along the axis and axial displacement restrained at both ends. The condition is purely geometric and consists of an upper bound on the mean radius of thickness ratio for a given fixed value of the length to mean radius ratio, above which the mode with one half wave in radial displacement along the axis ceases to exist. The proof is based on enforcing two basic lemmas concerned with the simplicity of the eigenvalues of the shell and the uniform ordering of these eigenvalues with the number of nodes of their corresponding radial displacement eigenfunctions.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 74; Feb. 8
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  • 6
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    Effect of elastic end rings on the eigenfrequencies of thin cylinders (1981)
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    Publication Date: 2011-08-18
    Description: The effect of elastic end rings on the eigenfrequencies of thin cylindrical shells is studied by using an exact solution of the linear eigenvalue problem. The out-of-plane and torsional rigidities of the rings are responsible for the overall shell stiffness. Considerable mode interaction exists for modes with low circumferential wave numbers when the mass of the ring is comparable with that of the shell. The hypothetical simply supported and clamped boundary conditions are practically impossible to realize with a finite-mass ring for relatively short and thin shells.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 74; Jan. 8
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  • 7
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    Stress-intensity factors and crack-opening displacements for round compact specimens (1981)
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    Publication Date: 2011-08-18
    Description: An improved method of boundary collocation based on the complex variable analysis of Muskhelishvili (1953) is applied to the two-dimensional stress analysis of round compact specimens with pin-loaded holes. Stress intensity factors and crack opening displacements are calculated for various round compact specimens as a function of crack-length-to-specimen-width ratios. A wide-range equation for the stress intensity factors and equations for crack-surface displacements and load-point displacements are developed.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 17; Dec. 198
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  • 8
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    Multi-parameter yield zone model for predicting spectrum crack growth (1981)
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    Publication Date: 2011-08-18
    Description: A phenomenological load interaction model referred to as the Multi-Parameter Yield Zone model is presented which accounts for crack growth retardation caused by previous overloads, acceleration due to current overloads, and underload effects. In the present model, load interaction effects are calculated utilizing a residual stress intensity concept. Crack growth retardation and acceleration are accounted for by decreasing or increasing, respectively, the effective stress ratio used in a modified Forman's (1967) crack growth equation. Results of spectrum crack growth predictions for 2219-T851 aluminum are presented.
    Keywords: STRUCTURAL MECHANICS
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  • 9
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    A crack-closure model for predicting fatigue crack growth under aircraft spectrum loading (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The present paper is concerned with the development and application of an analytical model of cyclic crack growth that includes the effects of crack closure. The model was based on a concept like the Dugdale model, but was modified to leave plastically deformed material in the wake of the advancing crack tip. The model was used to correlate crack growth rates under constant-amplitude loading and to predict crack growth under aircraft spectrum loading on 2219-T851 aluminum alloy plate material. The predicted crack growth lives agreed well with experimental data. The ratio of predicted-to-experimental lives ranged from 0.66 to 1.48.
    Keywords: STRUCTURAL MECHANICS
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  • 10
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    A root-mean-square approach for predicting fatigue crack growth under random loading (1981)
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    Publication Date: 2011-08-18
    Description: A method for predicting fatigue crack growth under random loading which employs the concept of Barsom (1976) is presented. In accordance with this method, the loading history for each specimen is analyzed to determine the root-mean-square maximum and minimum stresses, and the predictions are made by assuming the tests have been conducted under constant-amplitude loading at the root-mean-square maximum and minimum levels. The procedure requires a simple computer program and a desk-top computer. For the eleven predictions made, the ratios of the predicted lives to the test lives ranged from 2.13 to 0.82, which is a good result, considering that the normal scatter in the fatigue-crack-growth rates may range from a factor of two to four under identical loading conditions.
    Keywords: STRUCTURAL MECHANICS
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  • 11
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    Some approximations in the linear dynamic equations of thin cylinders (1981)
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    Publication Date: 2011-08-18
    Description: Theoretical analysis is performed on the linear dynamic equations of thin cylindrical shells to find the error committed by making the Donnell assumption and the neglect of in-plane inertia. At first, the effect of these approximations is studied on a shell with classical simply supported boundary condition. The same approximations are then investigated for other boundary conditions from a consistent approximate solution of the eigenvalue problem. The Donnell assumption is valid at frequencies high compared with the ring frequencies, for finite length thin shells. The error in the eigenfrequencies from omitting tangential inertia is appreciable for modes with large circumferential and axial wavelengths, independent of shell thickness and boundary conditions.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 76; June 22
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  • 12
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    Cyclic plasticity models and application in fatigue analysis (1981)
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    Publication Date: 2011-08-18
    Description: An analytical procedure for prediction of the cyclic plasticity effects on both the structural fatigue life to crack initiation and the rate of crack growth is presented. The crack initiation criterion is based on the Coffin-Manson formulae extended for multiaxial stress state and for inclusion of the mean stress effect. This criterion is also applied for the accumulated damage ahead of the existing crack tip which is assumed to be related to the crack growth rate. Three cyclic plasticity models, based on the concept of combination of several yield surfaces, are employed for computing the crack growth rate of a crack plane stress panel under several cyclic loading conditions.
    Keywords: STRUCTURAL MECHANICS
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  • 13
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    Wind loads for bar-truss structures (1981)
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    Publication Date: 2011-08-18
    Description: An analysis method developed to calculate the wind loads on the nodes or joints of the truss type support structure of the 64 meter antenna is described. The method uses the CBAR element and GRID coordinate cards of the NASTRAN or IDEAS structural analysis programs as inputs to the computer model of the structure. Cross flow principles and vector analysis are also used in the analysis. The algorithms used are described and probable accuracy of the solution is discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: The Telecommun. and Data Acquisition; p 149-153
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  • 14
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    Temperature-dependent creep buckling of plates (1981)
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    Publication Date: 2011-08-18
    Description: Time-dependent lateral deflection of flat rectangular plates is predicted by the Norton-Bailey (Norton 1929, Bailey 1935) power law for material creep. The plates have a through-thickness steady-state temperature distribution, and the effects are considered by using Maxwell's law to modify the power creep law. Equations are derived for creep exponents of 3 and 5, using the sandwich plate element to predict creep buckling of plates. Predictions of creep buckling with a temperature variation between the inner and outer plate surfaces are found to be somewhat dependent on the creep buckling relationship assumed. When significant scatter justifies a variation in the creep constants up to an order of magnitude, discrepancies in predictions using the two exponents are reasonable, and for one engineering material, the predictions have the same degree of agreement with experimental data as have the respective creep laws.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Thermal Stresses; 4; Apr. 198
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  • 15
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    Vibrations of three-dimensional pipe systems with acoustic coupling (1981)
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    Publication Date: 2011-08-18
    Description: A general algorithm is developed to calculate the beam-type dynamic response of three dimensional multiplane finite length pipe systems, consisting of elbow and straight ducts with continuous interfaces. Emphasis is on secondary acoustic wave effects giving rise to coupling mechanisms; and the simulation accounts for one-dimensional elastoacoustic coupling from a plane acoustic wave and secondary loads resulting from wave asymmetries. The transfer matrix approach is adopted in modeling the elastodynamics of each duct, with allowance for distribution loads. Secondary loads from plane wave distortion are considered with a solution of the Helmholtz equation in an equivalent rigid waveguide, and effects of path imperfection are introduced as a perturbation from the hypothetical perfectly straight pipe. Computations indicate that the one-dimensional acoustic assumption is valid for frequencies below one-half the first cut-off frequency, and the three-dimensional acoustic effects produce an increase in response levels near and above cut-off.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 78; Sept. 8
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  • 16
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    Structural synthesis - Its genesis and development (1981)
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    Publication Date: 2011-08-18
    Description: An historical account is given of the development, from its conception in 1960, of the structural synthesis method. While synthesis techniques lag behind analytical ones in both sophistication and application, the structural design procedures created by combining finite element analysis and mathematical programming algorithms have progressed to the point of maturity. As in the case of finite element analysis, use and acceptance of structural synthesis methodology depends on the development and distribution of easily used and well-documented, production-quality computer programs. Attention is given such elementary applications of synthesis methods as the three-bar truss, an integrally stiffened waffle plate, a stiffened cylindrical shell, aircraft fuselage window panels, the structural efficiency of graphite-epoxy hat-stiffened panels, and an idealized delta wing.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 19; Oct. 198
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  • 17
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    Green's function for cracks of equal length from a circular hole in an infinite sheet (1981)
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    Publication Date: 2011-08-18
    Description: Stress-intensity factors are obtained for twin collinear cracks emanating from a hole in an infinite plate. Point forces that tend to make the crack surfaces separate and slide are applied to one of the cracks. A conformal mapping and the Muskelishvili formulation involving series representation of the Kolosov stress functions are used to derive the solutions. The variation of stress-intensity factor with crack length and with point of application of the loads is presented for both crack tips.
    Keywords: STRUCTURAL MECHANICS
    Type: Res Mechanica Letters; 1; Dec. 198
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  • 18
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    An empirical stress-intensity factor equation for the surface crack (1981)
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    Publication Date: 2011-08-18
    Description: This paper presents an empirical stress-intensity factor equation for a surface crack as a function of parametric angle, crack depth, crack length, plate thickness and plate width for tension and bending loads. The stress-intensity factors used to develop the equation were obtained from a previous three-dimensional, finite-element analysis of semielliptical surface cracks in finite elastic plates subjected to tension or bending loads. A wide range of configuration parameters was included in the equation. The ratios of crack length to plate thickness and the ratios of crack depth to crack length ranged from 0 to 1.0. The effects of plate width on stress-intensity variations along the crack front were also included. The equation was used to predict patterns of surface-crack growth under tension or bending fatigue loads. The equation was also used to correlate surface-crack fracture data for a brittle epoxy material within + or - 10 percent for a wide range of crack shapes and crack sizes.
    Keywords: STRUCTURAL MECHANICS
    Type: Engineering Fracture Mechanics; 15; 1-2,; 1981
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  • 19
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    Computational methods in nonlinear structural and solid mechanics; Proceedings of the Symposium, Washington, D.C., October 6-8, 1980. Symposium sponsored by the George Washington University and NASA (1981)
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    Publication Date: 2016-03-09
    Description: Topics discussed include computational strategies for nonlinear problems in structural mechanics, time integration techniques and the numerical solution of nonlinear algebraic equations, material characterization and nonlinear fracture mechanics, nonlinear interaction problems, and seismic response and the nonlinear analysis of concrete structures. Also considered are nonlinear problems for nuclear reactors, crash dynamics and impact problems, nonlinear problems of fibrous composites and advanced nonlinear applications, and computerized symbolic manipulation and nonlinear analysis software systems.
    Keywords: STRUCTURAL MECHANICS
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  • 20
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    Methods and models for predicting fatigue crack growth under random loading (1981)
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    Publication Date: 2016-03-09
    Description: Papers are presented in the volume summarizing the baseline data, methodology, procedures, and results of a round-robin analysis which was conducted to predict the fatigue crack growth in 2219-T851 aluminum center-cracked specimens subjected to flight loading in random cycle-by-cycle format. The objective of the analysis was to assess whether data from constant-amplitude fatigue crack growth tests on center-cracked specimens can be used to predict fatigue crack growth lives under random loading. The following approaches are discussed in detail: a root-mean-square approach, a crack-closure model, a multi-parameter yield zone model, and a load-interaction model.
    Keywords: STRUCTURAL MECHANICS
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  • 21
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    On Hybrid and mixed finite element methods (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Three versions of the assumed stress hybrid model in finite element methods and the corresponding variational principles for the formulation are presented. Examples of rank deficiency for stiffness matrices by the hybrid stress model are given and their corresponding kinematic deformation modes are identified. A discussion of the derivation of general semi-Loof elements for plates and shells by the hybrid stress method is given. It is shown that the equilibrium model by Fraeijs de Veubeke can be derived by the approach of the hybrid stress model as a special case of semi-Loof elements.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-175551 , NAS 1.26:175551
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  • 22
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    Finite element forced vibration analysis of rotating cyclic structures (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: A capability was added to the general purpose finite element program NASTRAN Level 17.7 to conduct forced vibration analysis of tuned cyclic structures rotating about their axes of symmetry. The effects of Coriolis and centripetal accelerations together with those due to linear acceleration of the axis of rotation were included. The theoretical development of this capability is presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165430 , NAS 1.26:165430 , D2536-941008
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  • 23
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    Forced vibration analysis of rotating cyclic structures in NASTRAN (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: A new capability was added to the general purpose finite element program NASTRAN Level 17.7 to conduct forced vibration analysis of tuned cyclic structures rotating about their axis of symmetry. The effects of Coriolis and centripetal accelerations together with those due to linear acceleration of the axis of rotation were included. The theoretical, user's, programmer's and demonstration manuals for this new capability are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165429 , NAS 1.26:165429 , D2536-941007
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  • 24
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    Line-spring model for surface cracks in a Reissner plate (1981)
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    Publication Date: 2019-06-28
    Description: In this paper the line-spring model developed by Rice and Levy for a surface crack in elastic plates is reconsidered. The problem is formulated by using Reissner's plate bending theory. For the plane strain problem of a strip containing an edge crack and subjected to tension and bending new expressions for stress intensity factors are used which are valid up to a depth-to-thickness ratio of 0.8. The stress intensity factors for a semi-elliptic and a rectangular crack are calculated. Considering the simplicity of the technique and the severity of the underlying assumptions, the results compare rather well with the existing finite element solutions.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Engineering Science; 19; 10, 1; 1981
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  • 25
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    On numerical nonlinear analysis of highly flexible spinning cantilevers (1981)
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    Publication Date: 2019-06-28
    Description: The general nonlinear discretized equations of motion of spinning elastic solids and structures are derived as a set of nonlinear ordinary differential equations for the case when the strain-displacement and velocity-displacement relations are nonlinear up to the second order. It is shown that the cost of generation of such equations is proportional to the fourth power of the number of degrees of freedom. A computer program is written to automatically generate the equations for the case of spinning cantilevers with initial imperfections. The types and the number of the coordinate functions used in the trial solution are parameters of the program.
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  • 26
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    Mixed models and reduced/selective integration displacement models for nonlinear analysis of curved beams (1981)
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    Publication Date: 2019-06-28
    Description: Simple mixed models are developed for use in the geometrically nonlinear analysis of deep arches. A total Lagrangian description of the arch deformation is used, the analytical formulation being based on a form of the nonlinear deep arch theory with the effects of transverse shear deformation included. The fundamental unknowns comprise the six internal forces and generalized displacements of the arch, and the element characteristic arrays are obtained by using Hellinger-Reissner mixed variational principle. The polynomial interpolation functions employed in approximating the forces are one degree lower than those used in approximating the displacements, and the forces are discontinuous at the interelement boundaries. Attention is given to the equivalence between the mixed models developed herein and displacement models based on reduced integration of both the transverse shear and extensional energy terms. The advantages of mixed models over equivalent displacement models are summarized. Numerical results are presented to demonstrate the high accuracy and effectiveness of the mixed models developed and to permit a comparison of their performance with that of other mixed models reported in the literature.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering; 17; Apr. 198
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  • 27
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    A Galerkin type finite element method for rotary-wing aeroelasticity in hover and forward flight (1981)
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    Publication Date: 2019-06-28
    Description: A Galerkin finite element method for the spatial discretization of the nonlinear, nonselfadjoint, partial differential equations governing rotary-wing aeroelasticity is presented. This method reduces algebraic manipulative labor significantly when compared to the global Galerkin method based on assumed modes. Furthermore, the Galerkin finite element method is ideally suited to treat rotor blades with discontinuous mass and stiffness distribution and structurally redundant configurations as they appear in bearingless rotors. Implementation of the method is illustrated for the coupled flap-lag aeroelastic problem of hingeless rotor blades in hover and forward flight. Numerical results for stability and response illustrate the numerical properties and convergence behavior of the method. It is concluded that the Galerkin finite element method is a practical tool for solving rotary-wing aeroelastic stability and response problems.
    Keywords: STRUCTURAL MECHANICS
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  • 28
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    Optimum structural design with plate bending elements - A survey (1981)
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    Publication Date: 2019-06-28
    Description: A survey is presented of recently published papers in the field of optimum structural design of plates, largely with respect to the minimum-weight design of plates subject to such constraints as fundamental frequency maximization. It is shown that, due to the availability of powerful computers, the trend in optimum plate design is away from methods tailored to specific geometry and loads and toward methods that can be easily programmed for any kind of plate, such as finite element methods. A corresponding shift is seen in optimization from variational techniques to numerical optimization algorithms. Among the topics covered are fully stressed design and optimality criteria, mathematical programming, smooth and ribbed designs, design against plastic collapse, buckling constraints, and vibration constraints.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 19; Apr. 198
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  • 29
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    Vibration and local instability of thermally stressed plates (1981)
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    Publication Date: 2019-06-28
    Description: The vibration and buckling of a double wedge square cantilever plate has been investigated. It is shown that the free vibration modes, which occur at Delta T ref = 0, transition into the buckled modes which occur at Delta T ref = Delta T ref-cr for the respective mode. Delta T ref-cr for a particular mode is defined as the magnitude of thermal load at which the frequency of the particular mode vanishes. The analysis yields the same number of buckling eigenvalues and buckling modes as there are vibration eigenvalues and vibration modes. Gradual application of the load in the analysis permits the change in each vibration frequency of interest and its associated mode to be followed up to the load at which the frequency of the mode becomes zero. This constitutes the limit of linear theory. As the load is increased, the thin edges of the plate begin to deform during vibration. This local deformation, which begins in the vibration mode, is shown to transition into the phenomena of local edge buckling at Delta T ref-cr for the mode.
    Keywords: STRUCTURAL MECHANICS
    Type: Computer Methods in Applied Mechanics and Engineering; 25; Mar. 198
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  • 30
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    Design considerations for composite fuselage structure of commercial transport aircraft (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The structural, manufacturing, and service and environmental considerations that could impact the design of composite fuselage structure for commercial transport aircraft application were explored. The severity of these considerations was assessed and the principal design drivers delineated. Technical issues and potential problem areas which must be resolved before sufficient confidence is established to commit to composite materials were defined. The key issues considered are: definition of composite fuselage design specifications, damage tolerance, and crashworthiness.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-159296 , LR-29540
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  • 31
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    Application of the line-spring model to a cylindrical shell containing a circumferential or axial part-through crack (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An approximate solution was obtained for a cylindrical shell containing a part-through surface crack. It was assumed that the shell contains a circumferential or axial semi-elliptic internal or external surface crack and was subjected to a uniform membrane loading or a uniform bending moment away from the crack region. A Reissner type theory was used to account for the effects of the transverse shear deformations. The stress intensity factor at the deepest penetration point of the crack was tabulated for bending and membrane loading by varying three dimensionless length parameters of the problem formed from the shell radius, the shell thickness, the crack length, and the crack depth. The upper bounds of the stress intensity factors are provided by the results of the elasticity solution obtained from the axisymmetric crack problem for the circumferential crack, and that found from the plane strain problem for a circular ring having a radial crack for the axial crack. The line-spring model gives the expected results in comparison with the elasticity solutions. Results also compare well with the existing finite element solution of the pressurized cylinder containing an internal semi-elliptic surface crack.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-164058
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    Design and fabrication of a stringer stiffened discrete-tube actively cooled panel for a hypersonic aircraft (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A 0.61 x 1.22 m (2 x 4 ft) test panel was fabricated and delivered to the Langley Research Center for assessment of the thermal and structural features of the optimized panel design. The panel concept incorporated an aluminum alloy surface panel actively cooled by a network of discrete, parallel, redundant, counterflow passage interconnected with appropriate manifolding, and assembled by adhesive bonding. The cooled skin was stiffened with a mechanically fastened conventional substructure of stringers and frames. A 40 water/60 glycol solution was the coolant. Low pressure leak testing, radiography, holography and infrared scanning were applied at various stages of fabrication to assess integrity and uniformity. By nondestructively inspecting selected specimens which were subsequently tested to destruction, it was possible to refine inspection standards as applied to this cooled panel design.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-3403 , REPT-7430-927001
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    Design data for brazed Rene 41 honeycomb sandwich (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Strength data, creep data and residual strength data after cyclic thermal exposure were obtained at temperatures from 78 K to 1144 K (-320 F to 1600 F). The influences of face thickness, core depth, core gage, cell size and thermal/stress exposure conditions on the mechanical design properties were investigated. A braze alloy and process was developed that is adequate to fully develop the strength of the honeycomb core while simultaneously solution treating and aging the Rene 41 fact sheets. New test procedures and test specimen configurations were developed to avoid excessive thermal stresses during cyclic thermal exposure.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-3382 , D180-26187-1
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    Equivalence of macroscopic and microscopic Griffith conditions for subcritical crack growth (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Exact relations are derived for a simple bond-snapping model of fracture and numerical results from a previous work are presented. A lattice model with a nonlinear cohesive force law is then considered. In both cases, the results confirm the equivalence of the microscopic and macroscopic Griffith conditions. The Griffith stress intensity is to be identified with the quiescent stress intensity.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 17; June 198
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  • 35
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    Structural analysis of general shells. Volume 2: User instructions for STAGSC-1 (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165671 , LMSC-D633873
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  • 36
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    Stresses in adhesively bonded joints - A closed-form solution (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The general plane strain problem of adhesively bonded structures consisting of two different, orthotropic adherends is considered, under the assumption that adherend thicknesses are constant and small in relation to the lateral dimensions of the bonded region, so that they may be treated as plates. The problem is reduced to a system of differential equations for the adhesive stresses which is solved in closed form, with a single lap joint and a stiffened plate under various loading conditions being considered as examples. It is found that the plate theory used in the analysis not only predicts the correct trend for adhesive stresses but gives surprisingly accurate results, the solution being obtained by assuming linear stress-strain relations for the adhesive.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Composite Materials; 15; May 1981
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  • 37
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    One dimensional modelling of failure in laminated plates by delamination buckling (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: When low speed objects impact composite laminated plates delamination may result. Under inplane compression such delaminations may buckle and tend to enlarge the delaminated area which can lead to loss of global plate stability. This process is modelled here in a first attempt by a delaminating beam-column wherein the local delamination growth, stability and arrest are governed by a fracture mechanics-based energy release rate criterion.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Solids and Structures; 17; 11, 1; 1981
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  • 38
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    Magnetically induced cylindrical stress waves in a thermoelastic conductor (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The problem of stress wave generation in a linear thermoelastic solid by a pulsed magnetic field is investigated both analytically and experimentally for a cylindrically symmetric conducting solid. A dynamic response analysis is developed to correlate magnetic, thermal, and stress fields in the solid with the time history of the electric current. In the experiment, a transient magnetic field was applied normal to a large conducting plate with a circular hole. Initially the field was confined to the interior of the circular hole. The field was generated by discharging a large capacitor bank through a solenoidal coil. The plane-stress cylindrical stress waves are 1-D in nature. The relative effects of the magnetic body force and thermoelastic stresses, both generated by the electromagnetic field, are assessed.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Solids and Structures; 17; 11, 1; 1981
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  • 39
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    Recent advances in reduction methods for nonlinear problems (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Status and some recent developments in the application of reduction methods to nonlinear structural mechanics problems are summarized. The aspects of reduction methods discussed herein include: (1) selection of basis vectors in nonlinear static and dynamic problems, (2) application of reduction methods in nonlinear static analysis of structures subjected to prescribed edge displacements, and (3) use of reduction methods in conjunction with mixed finite element models. Numerical examples are presented to demonstrate the effectiveness of reduction methods in nonlinear problems. Also, a number of research areas which have high potential for application of reduction methods are identified.
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  • 40
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    Development of an orthotropic hole element (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: A finite element was developed which adequately represents the state of stress in the region around a circular hole in orthotropic material experiencing reasonably general loading. This was achieved with a complementary virtual work formulation of the stiffness and stress matrices for a square element with center circular hole. The assumed stress state provides zero shearing stress on the hole boundary, so the element is suitable for problems involving load transfer without friction. The element has been implemented in the NASTRAN computer program, and sample problem results are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165759 , LG81ER0159
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  • 41
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    Global function approach in structural analysis: Basic approach, numerical results (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The structural response to a given environment is described by the differential equations of motion of deformable bodies. Analytic solutions of such problems for a reasonably large class of structural configurations are not within the realm of the possible. Consequently, the mathematical problem is recast into a numerical problem for solution on the computer. New technology in the space and energy fields led to a growing demand for accurate analysis which at times cannot be met due to the limits set by available budgets for computer time. In response to this need for more efficient numerical analysis, the possibilities of reducing the number of freedoms in the system through a revival of the global function approach were explored.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165669
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  • 42
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    Tension-tension fatigue behavior of the Space Shuttle strain-isolation-pad material (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The room temperature fatigue behavior of 0.41-cm (0.16-in) thick strain-isolation-pad (SIP) material was explored in a series of constant- and random-amplitude loading tests. The SIP material is used on the Space Shuttle to isolate the ceramic insulating tiles from the strains and deflections of the aluminum alloy airframe. In all tests, 12.7 by 12.7 cm (5.0 by 5.0 in) SIP specimens were subjected to tension-tension loading in the through-the-thickness direction at a frequency of 10 Hz. When subjected to cyclic loading, the SIP material exhibited a monotonic increase in thickness and a monotonic increase in tensile tangent moduli. The rate of thickness growth increased with increasing test stress level and decreased with increasing number cycles endured. Power law equations were found to provide a good representation of the thickness growth rate data. Tensile tangent moduli increased by as much as 80 percent during fatigue tests. Simple cumulative damage fatigue models predicted the mean thickness growth under random-amplitude loading with reasonable accuracy (factor of 2 on life).
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-83183
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  • 43
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    Thermal expansion properties of composite materials (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Thermal expansion data for several composite materials, including generic epoxy resins, various graphite, boron, and glass fibers, and unidirectional and woven fabric composites in an epoxy matrix, were compiled. A discussion of the design, material, environmental, and fabrication properties affecting thermal expansion behavior is presented. Test methods and their accuracy are discussed. Analytical approaches to predict laminate coefficients of thermal expansion (CTE) based on lamination theory and micromechanics are also included. A discussion is included of methods of tuning a laminate to obtain a near-zero CTE for space applications.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165632
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    Some experiences with active control of aeroelastic response (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Flight and wind tunnel tests were conducted and multidiscipline computer programs were developed as part of investigations of active control technology conducted at the NASA Langley Research Center. Unsteady aerodynamics approximation, optimal control theory, optimal controller design, and the Delta wing and DC-10 models are described. The drones for aerodynamics and structural testing (DAST program) for evaluating procedures for aerodynamic loads prediction and the design of active control systems on wings with significant aeroelastic effects is described as well as the DAST model used in the wind tunnel tests.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-83179
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  • 45
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    Photoelastic techniques for the complete determination of stresses in composite structures (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Three methods of photoelastic analysis are examined. The first method is an extension of the oblique incidence technique in which the model (or the light beam) is rotated about one of the material symmetry axes. In the second method, transmission and reflection photoelastic responses are combined. The third method requires the drilling of small holes and the determination of the fringe orders at selected points on the hole boundary. The three methods are applied to an orthotropic circular disk under diametral compression. Results are compared with strain gage data.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-164689
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  • 46
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    The reduced order model problem in distributed parameter systems adaptive identification and control (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The basic assumption that a large space structure can be decoupled preceding the application of reduced order active control was considered and alternative solutions to the control of such structures (in contrast to the strict modal control) were investigated. The transfer function matrix from the actuators to the sensors was deemed to be a reasonable candidate. More refined models from multivariable systems theory were studied and recent results in the multivariable control field were compared with respect to theoretical deficiencies and likely problems in application to large space structures.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-164670
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  • 47
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    Cracked shells under skew-symmetric loading (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The general problem of a shell containing a through crack in one of the principal planes of curvature and under general skew-symmetric loading is considered. By employing a Reissner type shell theory which takes into account the effect of transverse shear strains, all boundary conditions on the crack surfaces are satisfied separately. Consequently, unlike those obtained from the classical shell theory, the angular distributions of the stress components around the crack tips are shown to be identical to the distributions obtained from the plane and anti-plane elasticity solutions. Results are given for axially and circumferentially cracked cylindrical shells, spherical shells, and toroidal shells under uniform in-plane shearing, out of plane shearing, and torsion. The problem is formulated for specially orthostropic materials, therefore, the effect of orthotropy on the results is also studied.
    Keywords: STRUCTURAL MECHANICS
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  • 48
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    Bifurcation and post-buckling analysis of laminated composite plates via reduced basis technique (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A reduced basis technique and a problem-adaptive computational algorithm are presented for the bifurcation and post-buckling analysis of laminated anisotropic plates. The computational algorithm can be conveniently divided into three distinct stages. The first stage is that of determining the bifurcation point. The plate is discretized by using displacement finite element (or finite difference) models. The special symmetries exhibited by the response of the anisotropic plate are used to reduce the size of the analysis region. The vector of unknown nodal parameters is expressed as a linear combination of a small number of basis vectors, and a Rayleigh-Ritz technique is used to approximate the finite element equations by a small system of algebraic equations. The reduced equations are used to determine the bifurcation point and the associated eigenmode of the panel. In the second stage of the bifurcation buckling mode is used to obtain a nonlinear solution in the vicinity of the bifurcation point and new (updated) sets of basis vectors and reduced equations are generated. In the third stage the reduced equations are used to trace the post-buckling paths. The effectiveness of the proposed technique for predicting the bifurcation and post-buckling behavior of plates is demonstrated by means of numerical examples for plates loaded by means of prescribed edge displacements.
    Keywords: STRUCTURAL MECHANICS
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    Vibrations of cantilevered shallow cylindrical shells of rectangular planform (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A cantilevered, shallow shell of circular cylindrical curvature and rectangular planform exhibits free vibration behavior which differs considerably from that of a cantilevered beam or of a flat plate. Some numerical results can be found for the problem in the previously published literature, mainly obtained by using various finite element methods. The present paper is the first definitive study of the problem, presenting accurate non-dimensional frequency parameters for wide ranges of aspect ratio, shallowness ratio and thickness ratio. The analysis is based upon shallow shell theory. Numerical results are obtained by using the Ritz method, with algebraic polynomial trial functions for the displacements. Convergence is investigated, with attention being given both to the number of terms taken for each co-ordinate direction and for each of the three components of displacement. Accuracy of the results is also established by comparison with finite element results for shallow shells and with other accurate flat plate solutions.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 78; Oct. 8
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  • 50
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    Interlaminar stress singularities at a straight free edge in composite laminates (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A quasi-three-dimensional finite-element analysis was used to analyze the edge-stress problem in four-ply, composite laminates. The seven laminates that were considered belong to the laminate family where the outer ply angle is between 0 and 90 deg. Systematic convergence studies were made to explore the existence of stress singularities near the free edge. The present analysis appears to confirm the existence of stress singularities at the intersection of the interface and the free edge. The power of the stress singularity was the same for all seven laminates considered.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 14; 1-2,; 1981
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  • 51
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    Boundary-layer effects in composite laminates: Free-edge stress singularities, part 6 (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A rigorous mathematical model was obtained for the boundary-layer free-edge stress singularity in angleplied and crossplied fiber composite laminates. The solution was obtained using a method consisting of complex-variable stress function potentials and eigenfunction expansions. The required order of the boundary-layer stress singularity is determined by solving the transcendental characteristic equation obtained from the homogeneous solution of the partial differential equations. Numerical results obtained show that the boundary-layer stress singularity depends only upon material elastic constants and fiber orientation of the adjacent plies. For angleplied and crossplied laminates the order of the singularity is weak in general.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165440 , NAS 1.26:165440
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    Analysis of cracks emanating from a circular hole in unidirectional fiber reinforced composites, part 2 (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: An analytical method is developed for cracks emanating from a circular hole in an off-axis unidirectional fiber-reinforced composite. The method which is formulated by using conservation laws of elasticity and fundamental relationships in anisotropic fracture mechanics, provides a convenient and accurate means to examine the complicated crack behavior, when used in conjunction with a suitable numerical scheme such as the finite element method. The formulation is eventually reduced to a system of linear algebraic equations of mixed-mode stress intensity factors. Fracture parameters, describing crack-tip deformation and fracture in the composite, are obtained explicitly. Effects of material anisotropy and crack/hole geometry are examined also. Of particular interest are the energy release rates associated with crack extension; their values are evaluated for various cases. Results show that mixed-mode stress intensity factors and energy release rates associated with the cracks emanating from a hole change very appreciably with fiber orientation in the composite. K sub 1 and G increase monotonically with increasing theta; but K sub 2 reaches its maximum at theta = 45 deg, and then decreases gradually as theta increases further.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165433 , NAS 1.26:165433
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    Viscoelastic analysis of adhesively bonded joints (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: In this paper an adhesively bonded lap joint is analyzed by assuming that the adherends are elastic and the adhesive is linearly viscoelastic. After formulating the general problem a specific example for two identical adherends bonded through a three parameter viscoelastic solid adhesive is considered. The standard Laplace transform technique is used to solve the problem. The stress distribution in the adhesive layer is calculated for three different external loads namely, membrane loading, bending, and transverse shear loading. The results indicate that the peak value of the normal stress in the adhesive is not only consistently higher than the corresponding shear stress but also decays slower.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME Transactions; vol. 48
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    Techniques for thermal sensitivity analysis (1981)
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    Publication Date: 2019-06-28
    Description: Techniques for computing the sensitivity of temperatures to changes in design variables needed for designing thermal protection systems are considered. It is shown that the choice of the most efficient technique depends on the ratio of number of temperature constraints to the number of design variables, as well as on the thermal analysis method employed. The analysis is specialized to the case of a structure modeled by finite elements, and an example of an insulation panel is used to demonstrate the techniques.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering; 17; Jan. 198
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  • 55
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    Effect of load eccentricity and substructure deformation on ultimate strength of shuttle orbiter thermal protection system (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The effect of load eccentricity and substructure deformation on the ultimate strength and stress displacement properties of the shuttle orbiter thermal protection system (TPS) was determined. The LI-900 Reusable Surface Insulation (RSI) tiles mounted on the .41 cm thick Strain Isolator Pad (SIP) were investigated. Substructure deformations reduce the ultimate strength of the SIP/tile TPS and increase the scatter in the ultimate strength data. Substructure deformations that occur unsymmetric to the tile can cause the tile to rotate when subjected to a uniform applied load. Load eccentricity reduces SIP/tile TPS ultimate strength and causes tile rotation.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-83182
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  • 56
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    Structural dynamics verification facility study (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The need for a structural dynamics verification facility to support structures programs was studied. Most of the industry operated facilities are used for highly focused research, component development, and problem solving, and are not used for the generic understanding of the coupled dynamic response of major engine subsystems. Capabilities for the proposed facility include: the ability to both excite and measure coupled structural dynamic response of elastic blades on elastic shafting, the mechanical simulation of various dynamical loadings representative of those seen in operating engines, and the measurement of engine dynamic deflections and interface forces caused by alternative engine mounting configurations and compliances.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-82675 , E-958
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  • 57
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    The crack problem for a half plane stiffened by elastic cover plates (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: An elastic half plane containing a crack and stiffened by a cover plate is discussed. The asymptotic nature of the stress state in the half plane around an end point of the stiffener to determine the likely orientation of a possible fracture initiation and growth was studied. The problem is formulated for an arbitrary oriented radial crack in a system of singular integral equations. For an internal crack and for an edge crack, the problem is solved and the stress intensity factors at the crack tips and the interface stress are calculated. A cracked half plane with two symmetrically located cover plates is also considered. It is concluded that the case of two stiffeners appears to be more severe than that of a single stiffener.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165776
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  • 58
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    Buckling loads for stiffened panels subjected to combined longitudinal compression and shear loadings: Results obtained with PASCO, EAL, and STAGS computer (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The shear buckling analyses used in PASCO are summarized. The PASCO analyses include the basic VIPASA analysis, which is essentially exact for longitudinal and transverse loads, and a smeared orthotropic solution which was added to alleviate a shortcoming in the VIPASA analysis. Buckling results are presented for six 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 provide calculations for the entire range of combinations of longitudinal compression and shear loadings.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-83194
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    Mission load dynamic tests of two undensified Space shuttle thermal protection system tiles (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Two tests of undensified Space Shuttle thermal protection tiles under combined static and dynamic loads were conducted. The tiles had a density of approximately 144 Kg/cum (LI900 tiles) and were mounted on a strain isolation pad which was 0.41 cm (.160 inch) thick. A combined static and dynamic mission stress histogram representative of the W-3 area of the wing of the orbiter vehicle was applied. The stress histogram was provided by the space shuttle project. Results presented include: tabulation of measured peak and root-mean-square (RMS) accelerations in both compression and tension; peak SIP stress in compression and tension, peak and RMS amplitude response ratios; lateral to vertical response ratios; response time histories; peak stress distributions (histograms), and SIP extension measured both with and without static tension at various mission times.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-83148
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  • 60
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    Computer program for nonlinear static stress analysis of shuttle thermal protection system: User's manual (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: User documentation is presented for a computer program which considers the nonlinear properties of the strain isolator pad (SIP) in the static stress analysis of the shuttle thermal protection system. This program is generalized to handle an arbitrary SIP footprint including cutouts for instrumentation and filler bar. Multiple SIP surfaces are defined to model tiles in unique locations such as leading edges, intersections, and penetrations. The nonlinearity of the SIP is characterized by experimental stress displacement data for both normal and shear behavior. Stresses in the SIP are calculated using a Newton iteration procedure to determine the six rigid body displacements of the tile which develop reaction forces in the SIP to equilibrate the externally applied loads. This user documentation gives an overview of the analysis capabilities, a detailed description of required input data and an example to illustrate use of the program.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-81856
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    Structures and Dynamics Division research and technology plans, fiscal year, 1981 (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The objectives, expected results, approach, and FY 81 milestones for the Structures and Dynamics Division's research program are presented. This information will be useful in program coordination with other government organizations in areas of mutual interest.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-83137
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    Photomechanical transducer (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Light absorbing ultra-thin films mounted under a fixed strain exhibit the behavior of an optomechanicalor photomechanical transducer. The transducer responds to light in a quick and reversible manner converting a time-variable light source into a time-variable mechanical stress easily monitored by a device such as a strain gage.
    Keywords: STRUCTURAL MECHANICS
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    Static and yawed-rolling mechanical properties of two type 7 aircraft tires (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Selected mechanical properties of 18 x 5.5 and 49 x 17 size, type 7 aircraft tires were evaluated. The tires were subjected to pure vertical loads and to combined vertical and lateral loads under both static and rolling conditions. Parameters for the static tests consisted of tire load in the vertical and lateral directions, and parameters for the rolling tests included tire vertical load, yaw angle, and ground speed. Effects of each of these parameters on the measured tire characteristics are discussed and, where possible, compared with previous work. Results indicate that dynamic tire properties under investigation were generally insensitive to speed variations and therefore tend to support the conclusion that many tire dynamic characteristics can be obtained from static and low speed rolling tests. Furthermore, many of the tire mechanical properties are in good agreement with empirical predictions based on earlier research.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-1863 , L-14125
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    Extension of oblique incidence method to photo-orthotropic-elasticity (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: With the interpretation of isochromatic and isoclinic fringes in transparent, birefringent, orthotropic composites established, efforts were in progress to determine the individual values of the principal stresses or strains. Several methods utilize the photoelastic results only partially and rely on numerical procedures. Others attempt to obtain the required information based entirely on experimental data. The classical oblique incidence technique as applied to transversely isotropic birefringent composites, is presented. The proposed extension is verified by applying it to the problem of an orthotropic half-plane subjected to an edge-load.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-164334
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    A Single-Expression Formula for Inverting Strain-Life and Stress-Strain Relationships (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Starting with the basic fatigue lift formula, an inversion formula is derived. The inversion formula is valid over the entire life range of engineering interest for all materials examined. Conformity between the two equations is extremely close, suitable for all engineering problems. The approach used to invert the life relation is also suitable for the inversion of other formulas involving the sum of two power-law terms.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165347
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    Lubrication fundamentals (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A lubricant is any substance that is used to reduce friction and wear and to provide smooth running and a satisfactory life for machine components. Lubrication fundamentals are discussed and the various lubrication mechanisms are defined. These include: hydrodynamic, elastohydrodynamic, mixed, boundary, and extreme pressure. Before the various lubrication mechanisms are presented, it is desirable to define conformal and nonconformal surfaces.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-81762 , E-825
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    A fundamental approach to adhesion: Synthesis, surface analysis, thermodynamics and mechanics (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Pretreated and primed Ti 6-4 surfaces were characterized by scanning electron microscopy/energy dispersive analysis of X-rays (SEM/EDAX) and electron spectroscopy for chemical analysis (ESCA). Fractured lap shear bonded Ti 6-4 specimens were also characterized by SEM/EDAX and ESCA. A number of surface techniques were used to characterize Ti02 powders.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-164229
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    MEGA16 - Computer program for analysis and extrapolation of stress-rupture data (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The computerized form of the minimum commitment method of interpolating and extrapolating stress versus time to failure data, MEGA16, is described. Examples are given of its many plots and tabular outputs for a typical set of data. The program assumes a specific model equation and then provides a family of predicted isothermals for any set of data with at least 12 stress-rupture results from three different temperatures spread over reasonable stress and time ranges. It is written in FORTRAN 4 using IBM plotting subroutines and its runs on an IBM 370 time sharing system.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-1809 , E-495
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    FRANOPP: Framework for analysis and optimization problems user's guide (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Framework for analysis and optimization problems (FRANOPP) is a software aid for the study and solution of design (optimization) problems which provides the driving program and plotting capability for a user generated programming system. In addition to FRANOPP, the programming system also contains the optimization code CONMIN, and two user supplied codes, one for analysis and one for output. With FRANOPP the user is provided with five options for studying a design problem. Three of the options utilize the plot capability and present an indepth study of the design problem. The study can be focused on a history of the optimization process or on the interaction of variables within the design problem.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165653
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    PASCO: Structural panel analysis and sizing code: Users manual - Revised (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A computer code denoted PASCO is described for analyzing and sizing uniaxially stiffened composite panels. Buckling and vibration analyses are carried out with a linked plate analysis computer code denoted VIPASA, which is included in PASCO. Sizing is based on nonlinear mathematical programming techniques and employs a computer code denoted CONMIN, also included in PASCO. Design requirements considered are initial buckling, material strength, stiffness and vibration frequency. A user's manual for PASCO is presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-80182 , NAS 1.15:80182
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    Test progress on the electrostatic membrane reflector (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An extemely lightweight type of precision reflector antenna, being developed for potential deployment from the space shuttle, uses electrostatic forces to tension a thin membrane and form it into a concave reflector surface. The typical shuttle-deployed antenna would have a diameter of 100 meters and an RMS surface smoothness of 10 to 1 mm for operation at 1 to 10 GHz. NASA Langley Research Center built and is currently testing a subscale (16 foot diameter) model of the membrane reflector portion of such an antenna. Preliminary test results and principal factors affecting surface quality are addressed. Factors included are the effect of the perimeter boundary, splicing of the membrane, the long-scale smoothness of commercial membranes, and the spatial controllability of the membrane using voltage adjustments to alter the electrostatic pressure. Only readily available commercial membranes are considered.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165792 , CR-2-998
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    An improved transverse shear deformation theory for laminated antisotropic plates (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An improved transverse shear deformation theory for laminated anisotropic plates under bending is presented. The theory eliminates the need for an arbitrarily chosen shear correction factor. For a general laminate with coupled bending and stretching, the constitutive equations connecting resultants with average displacements and rotations are derived. Simplified forms of these relations are also obtained for the special case of a symmetric laminate with uncoupled bending. The governing equation for this special case is obtained as a sixth-order equation for the normal displacement requiring prescription of the three physically natural bounday conditions along each edge. For the limiting case of isotropy, the present theory reduces to an improved version of Mindlin's theory. Numerical results are obtained from the present theory for an example of a laminated plate under cylindrical bending. Comparison with results from exact three-dimensional analysis shows that the present theory is more accurate than other theories of equivalent order.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-1903 , L-14533
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    Modal analysis using a Fourier analyzer, curve-fitting, and modal tuning (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The proposed modal test program differs from single-input methods in that preliminary data may be acquired using multiple inputs, and modal tuning procedures may be employed to define closely spaced frquency modes more accurately or to make use of frequency response functions (FRF's) which are based on several input locations. In some respects the proposed modal test proram resembles earlier sine-sweep and sine-dwell testing in that broadband FRF's are acquired using several input locations, and tuning is employed to refine the modal parameter estimates. The major tasks performed in the proposed modal test program are outlined. Data acquisition and FFT processing, curve fitting, and modal tuning phases are described and examples are given to illustrate and evaluate them.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-161886 , CAR-81-1
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  • 74
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    Vibrations of twisted rotating blades (1981)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: The literature dealing with vibrations of turbomachinery blades is voluminous, but the vast majority of it treats the blades as beams. In a previous paper a two-dimensional analytical procedure was developed and demonstrated on simple models of blades having camber. The procedure utilizes shallow shell theory along with the classical Ritz method for solving the vibration problem. Displacement functions are taken as algebraic polynomials. In the present paper the method is demonstrated on blade models having camber. Comparisons are first made with results in the literature for nonrotating twisted plates and various disagreements between results are pointed out. A method for depicting mode shape information is demonstrated, permitting one to examine all three components of displacement. Finally, the analytical procedure is demonstrated on rotating twisted blade modes, both without and with camber.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 81-DET-127 , American Society of Mechanical Engineers, Design Engineering Technical Conference; Sept. 20-23, 1981; Hartford, CT
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    Stress concentrations in cylindrically orthotropic composite plates with a circular hole (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The equations governing the distribution of the stresses in a cylindrically orthotropic plate with a circular hole are solved for the case when the plate is subjected to uniform uniaxial traction. Closed-form solutions are given for the circumferential stresses along the edge of the hole.
    Keywords: STRUCTURAL MECHANICS
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    Creep rupture of polymer-matrix composites (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The time-dependent creep-rupture process in graphite-epoxy laminates is examined as a function of temperature and stress level. Moisture effects are not considered. An accelerated characterization method of composite-laminate viscoelastic modulus and strength properties is reviewed. It is shown that lamina-modulus master curves can be obtained using a minimum of normally performed quality-control-type testing. Lamina-strength master curves, obtained by assuming a constant-strain-failure criterion, are presented along with experimental data, and reasonably good agreement is shown to exist between the two. Various phenomenological delayed failure models are reviewed and two (the modified rate equation and the Larson-Miller parameter method) are compared to creep-rupture data with poor results.
    Keywords: STRUCTURAL MECHANICS
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    Development of a unified numerical procedure for free vibration analysis of structures (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper presents the details of a unified numerical algorithm and the associated computer program developed for the efficient determination of natural frequencies and modes of free vibration of structures. Both spinning and nonspinning structures with or without viscous and/or structural damping may be solved by the current procedure; in addition, the program is capable of solving static problems with multiple load cases as well as the quadratic matrix eigenproblem associated with a finite dynamic element structural discretization.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering; 17; Feb. 198
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  • 78
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    Time-temperature effect in adhesively bonded joints (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The viscoelastic analysis of an adhesively bonded lap joint was reconsidered. The adherends are approximated by essentially Reissner plates and the adhesive is linearly viscoelastic. The hereditary integrals are used to model the adhesive. A linear integral differential equations system for the shear and the tensile stress in the adhesive is applied. The equations have constant coefficients and are solved by using Laplace transforms. It is shown that if the temperature variation in time can be approximated by a piecewise constant function, then the method of Laplace transforms can be used to solve the problem. A numerical example is given for a single lap joint under various loading conditions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165775
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    Wind loads on flat plate photovoltaic array fields (nonsteady winds) (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Techniques to predict the dynamic response and the structural dynamic loads of flat plate photovoltaic arrays due to wind turbulence were analyzed. Guidelines for use in predicting the turbulent portion of the wind loading on future similar arrays are presented. The dynamic response and the loads dynamic magnification factor of the two array configurations are similar. The magnification factors at a mid chord and outer chord location on the array illustrated and at four points on the chord are shown. The wind tunnel test experimental rms pressure coefficient on which magnification factors are based is shown. It is found that the largest response and dynamic magnification factor occur at a mid chord location on an array and near the trailing edge. A technique employing these magnification factors and the wind tunnel test rms fluctuating pressure coefficients to calculate design pressure loads due to wind turbulence is presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-164745 , DOE/JPL-954833-81/4 , JPL-9950-594
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    Self-adaptive predictor-corrector algorithm for static nonlinear structural analysis (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A multiphase selfadaptive predictor corrector type algorithm was developed. This algorithm enables the solution of highly nonlinear structural responses including kinematic, kinetic and material effects as well as pro/post buckling behavior. The strategy involves three main phases: (1) the use of a warpable hyperelliptic constraint surface which serves to upperbound dependent iterate excursions during successive incremental Newton Ramphson (INR) type iterations; (20 uses an energy constraint to scale the generation of successive iterates so as to maintain the appropriate form of local convergence behavior; (3) the use of quality of convergence checks which enable various self adaptive modifications of the algorithmic structure when necessary. The restructuring is achieved by tightening various conditioning parameters as well as switch to different algorithmic levels to improve the convergence process. The capabilities of the procedure to handle various types of static nonlinear structural behavior are illustrated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165410 , JP-81-1
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    Wind loads on flat plate photovoltaic array fields (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The results of an experimental analysis (boundary layer wind tunnel test) of the aerodynamic forces resulting from winds acting on flat plate photovoltaic arrays are presented. Local pressure coefficient distributions and normal force coefficients on the arrays are shown and compared to theoretical results. Parameters that were varied when determining the aerodynamic forces included tilt angle, array separation, ground clearance, protective wind barriers, and the effect of the wind velocity profile. Recommended design wind forces and pressures are presented, which envelop the test results for winds perpendicular to the array's longitudinal axis. This wind direction produces the maximum wind loads on the arrays except at the array edge where oblique winds produce larger edge pressure loads. The arrays located at the outer boundary of an array field have a protective influence on the interior arrays of the field. A significant decrease of the array wind loads were recorded in the wind tunnel test on array panels located behind a fence and/or interior to the array field compared to the arrays on the boundary and unprotected from the wind. The magnitude of this decrease was the same whether caused by a fence or upwind arrays.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-164454 , DOE/JPL-954833-81/3
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    A crack-closure model for predicting fatigue-crack growth under aircraft spectrum loading (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The development and application of an analytical model of cycle crack growth is presented that includes the effects of crack closure. The model was used to correlate crack growth rates under constant amplitude loading and to predict crack growth under aircraft spectrum loading on 2219-T851 aluminum alloy sheet material. The predicted crack growth lives agreed well with experimental data. The ratio of predicted to experimental lives ranged from 0.66 to 1.48. These predictions were made using data from an ASTM E24.06.01 Round Robin.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-81941
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    Structural tests on space shuttle thermal protection system constructed with nondensified and densified Li 900 and LI 2200 tile (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Structural tests were conducted on thermal protection systems (TPS) LI 900 and LI 2200 tiles and .41 cm and .23 cm thick strain isolation pads. The bond surface of selected tiles was densified to obtain improved strength. Four basic types of experiments were conducted including tension tests, substrate mismatch (initial imperfection) tests, tension loads eccentrically applied, and pressure loads applied rapidly to the tile top surface. A small initial imperfection mismatch (2.29 m spherical radius on the substrate) did not influence significantly the ultimate failure strength. Densification of the tile bond region improved the strength of TPS constructed both of LI 900 tile and of LI 2200 tile. Pressure shock conditions studied did not significantly affect the TPS strength.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-81903
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    Room temperature shear properties of the strain isolator pad for the shuttle thermal protection system (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Tests were conducted at room temperature to determine the shear properties of the strain isolator pad (SIP) material used in the thermal protection system of the space shuttle. Tests were conducted on both the .23 cm and .41 cm thick SIP material in the virgin state and after fifty fully reversed shear cycles. The shear stress displacement relationships are highly nonlinear, exhibit large hysteresis effects, are dependent on material orientation, and have a large low modulus region near the zero stress level where small changes in stress can result in large displacements. The values at the higher stress levels generally increase with normal and shear force load conditioning. Normal forces applied during the shear tests reduces the low modulus region for the material. Shear test techniques which restrict the normal movement of the material give erroneous stress displacement results. However, small normal forces do not significantly effect the shear modulus for a given shear stress. Poisson's ratio values for the material are within the range of values for many common materials. The values are not constant but vary as a function of the stress level and the previous stress history of the material. Ultimate shear strengths of the .23 cm thick SIP are significantly higher than those obtained for the .41 cm thick SIP.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-81900
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    Creep crack-growth: A new path-independent T sub o and computational studies (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Two path independent integral parameters which show some degree of promise as fracture criteria are the C* and delta T sub c integrals. The mathematical aspects of these parameters are reviewed. This is accomplished by deriving generalized vector forms of the parameters using conservation laws which are valid for arbitrary, three dimensional, cracked bodies with crack surface tractions (or applied displacements), body forces, inertial effects and large deformations. Two principal conclusions are that delta T sub c is a valid crack tip parameter during nonsteady as well as steady state creep and that delta T sub c has an energy rate interpretation whereas C* does not. An efficient, small displacement, infinitestimal strain, displacement based finite element model is developed for general elastic/plastic material behavior. For the numerical studies, this model is specialized to two dimensional plane stress and plane strain and to power law creep constitutive relations.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-168930 , NAS 1.26:168930
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    The axisymmetric elasticity problem for a laminated plate containing a circular hole (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The elasticity problem for a laminated thick plate which consists of two bonded dissimilar layers and which contains a circular hole is considered. The problem is formulated for arbitrary axisymmetric tractions on the hole surface by using the Love strain function. Through the expansion of the boundary conditions into Fourier series the problem is reduced to an infinite system of algebraic equations which is solved by the method of reduction. Of particular interest in the problem are the stresses along the interface as they relate to the question of delamination failure of the composite plate. These stresses are calculated and are observed to become unbounded at the hole boundary. An approximate treatment of the singular behavior of the stress state is presented and the stress intensity factors are calculated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-168759 , NAS 1.26:168759
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    Investigation of creep by use of closed loop servo-hydraulic test system (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Creep tests were conducted by means of a closed loop servo-controlled materials test system. These tests are different from the conventional creep tests in that the strain history prior to creep may be carefully monitored. Tests were performed for aluminum alloy 6061-0 at 150 C and monitored by a PDP 11/04 minicomputer at a preset constant plastic-strain rate prehistory. The results show that the plastic-strain rate prior to creep plays a significant role in creep behavior. The endochronic theory of viscoplasticity was applied to describe the observed creep curves. The concepts of intrinsic time and strain rate sensitivity function are employed and modified according to the present observation.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-168613 , G302-81-001
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  • 88
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    Finite-element modeling of layered, anisotropic composite plates and shells: A review of recent research (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Finite element papers published in the open literature on the static bending and free vibration of layered, anisotropic, and composite plates and shells are reviewed. A literature review of large-deflection bending and large-amplitude free oscillations of layered composite plates and shells is also presented. Non-finite element literature is cited for continuity of the discussion.
    Keywords: STRUCTURAL MECHANICS
    Type: Shock and Vibration Information Center The Shock and Vibration Digest, Vol. 13, No. 12; p 3-12
    Format: text
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    General description of nestable column structural and assembly technology (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The superior packaging characteristics of nestable column structural elements make this concept attractive for application to missions space shuttle missions requiring large and/or high stiffness, or complex structures. Photographs depict investigations pursued relative to defining structural and assembly technology using these structural elements. The neutral buoyancy facility assembly simulation tests and the large space structure mobile work station are featured.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-83255
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    Stress evaluations under rolling/sliding contacts (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The state of stress beneath traction drive type of contacts were analyzed. Computing stresses and stress reversals on various planes for points beneath the surface were examined. The effect of tangential and axial friction under gross slip conditions is evaluated with the models. Evaluations were performed on an RC (rolling contact) tester configuration and it is indicated that the classical fatigue stresses are not altered by friction forces typical of lubricated contact. Higher values of friction can result in surface shear reversal that exceeds the stresses at the depth of maximum shear reversal under rolling contact.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165561 , G7782
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    Elevated temperature fatigue testing of metals (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The major technology areas needed to perform a life prediction of an aircraft turbine engine hot section component are discussed and the steps required for life prediction are outlined. These include the determination of the operating environment, the calculation of the thermal and mechanical loading of the component, the cyclic stress-strain and creep behavior of the material required for structural analysis, and the structural analysis to determine the local stress-strain-temperature-time response of the material at the critical location in the components. From a knowledge of the fatigue, creep, and failure resistance of the material, a prediction of the life of the component is made. Material characterization and evaluation conducted for the purpose of calculating fatigue crack initiation lives of components operating at elevated temperatures are emphasized.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-82745 , E-1058
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    Dynamic behavior of continuous cantilevered pipes conveying fluid near critical velocities (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The plane motion of a cantilevered pipe conveying fluid is examined when the flow velocity is in the neighborhood of that generating flutter. In contrast to previous studies, the flow velocity is not prescribed as a constant, but is determined from the laws of motion. A system of two nonlinear partial differential equations which are coupled through the nonlinear terms is thereby obtained. The solution is found by the use of the Krylov-Bogoliubov averaging method and the results are discussed indicating the effect of nonlinearities.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 81-WA/APM-13
    Format: text
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  • 93
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    Analysis of interface cracks in adhesively bonded lap shear joints, part 4 (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Conservation laws of elasticity for nonhomogeneous materials were developed and were used to study the crack behavior in adhesively bonded lap shear joints. By using these laws and the fundamental relationships in fracture mechanics of interface cracks, the problem is reduced to a pair of linear algebraic equations, and stress intensity solutions can be determined directly by information extracted from the far field. The numerical results obtained show that: (1) in the lap-shear joint with a given adherend, the opening-mode stress intensity factor, (K sub 1) is always larger than that of the shearing-mode (K sub 2); (2) (K sub 1) is not sensitive to adherent thickness abut (K sub 2) increases rapidly with increasing thickness; and (3) (K sub 1) and (K sub 2) increase simultaneously as the interfacial crack length increases.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165438 , NAS 1.26:165438
    Format: application/pdf
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  • 94
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    Boundary layer thermal stresses in angle-ply composite laminates, part 1 (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Thermal boundary-layer stresses (near free edges) and displacements were determined by a an eigenfunction expansion technique and the establishment of an appropriate particular solution. Current solutions in the region away from the singular domain (free edge) are found to be excellent agreement with existing approximate numerical results. As the edge is approached, the singular term controls the near field behavior of the boundary layer. Results are presented for cases of various angle-ply graphite/epoxy laminates with (theta/-theta/theta/theta) configurations. These results show high interlaminar (through-the-thickness) stresses. Thermal boundary-layer thicknesses of different composite systems are determined by examining the strain energy density distribution in composites. It is shown that the boundary-layer thickness depends on the degree of anisotropy of each individual lamina, thermomechanical properties of each ply, and the relative thickness of adjacent layers. The interlaminar thermal stresses are compressive with increasing temperature. The corresponding residual stresses are tensile and may enhance interply delaminations.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165412 , NAS 1.26:165412
    Format: application/pdf
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  • 95
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    Effective constitutive relations for large repetitive frame-like structures (1981)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: Effective mechanical properties for large repetitive framelike structures are derived using combinations of strength of material and orthogonal transformation techniques. Symmetry considerations are used in order to identify independent property constants. The actual values of these constants are constructed according to a building block format which is carried out in the three consecutive steps: (1) all basic planar lattices are identified; (2) effective continuum properties are derived for each of these planar basic grids using matrix structural analysis methods; and (3) orthogonal transformations are used to determine the contribution of each basic set to the overall effective continuum properties of the structure.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-164521
    Format: application/pdf
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  • 96
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    Bending-torsion flutter of a highly swept advanced turboprop (1981)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Experimental and analytical results are presented for a bending-torsion flutter phenomena encountered during wind-tunnel testing of a ten-bladed, advanced, high-speed propeller (turboprop) model with thin airfoil sections, high blade sweep, low aspect ratio, high solidity and transonic tip speeds. Flutter occurred at free-stream Mach numbers of 0.6 and greater and when the relative tip Mach number (based on vector sum of axial and tangential velocities) reached a value of about one. The experiment also included two- and five-blade configurations. The data indicate that aerodynamic cascade effects have a strong destabilizing influence on the flutter boundary. The data was correlated with analytical results which include aerodynamic cascade effects and good agreement was found.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-82975 , E-1404 , NAS 1.15:82975 , 1982 Aerospace Congr. and Exposition; Jan 01, 1982; Anaheim, CA; United States
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  • 97
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    An inherent instability in fiber-reinforced composite laminates (1981)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Presented is a theory to predict the room-temperature shape of unsymmetric laminates. The theory is an extension of classical lamination theory and includes the effects of geometric nonlinearities. It is shown that the saddle shape predicted by the classical theory can actually be an unstable shape and a laminate will assume a cylindrical shape instead. The phenomena is coupled to the length, width, and thickness of the laminate.
    Keywords: STRUCTURAL MECHANICS
    Type: 1981 advances in aerospace structures and materials; Nov 15, 1981 - Nov 20, 1981; Washington, DC
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  • 98
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    Mixed models and reduced/selective integration displacement models for nonlinear shell analysis (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: One of the objectives of the present investigation is to identify classes of equivalent mixed models and reduced/selective integration displacement models for curved shell structures. A second objective is concerned with the identification of the spurious modes exhibited by various mixed models and their equivalent reduced integration displacement models. The merits of using mixed models are also evaluated. The mixed elements developed in the current investigation differ from those presented by Noor and Hartley (1977) by the fact that the stress resultants are discontinuous at interelement boundaries and, therefore, are eliminated on the element level. The high accuracy and effectiveness of the elements developed is demonstrated by means of numerical examples, taking into account three geometrically nonlinear problems of shallow shells.
    Keywords: STRUCTURAL MECHANICS
    Type: In: Nonlinear finite element analysis of plates and shells; Nov 15, 1981 - Nov 20, 1981; Washington, DC
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  • 99
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    Crack tip deformation and fatigue crack growth (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Recent research on fatigue crack growth is summarized. Topics discussed include the use of the differential stress intensity factor to characterize crack tip deformation, the use of the unzipping model to study the growth of microcracks and the fatigue crack growth in a ferritic-martensitic steel, and the development of a model of fatige crack growth threshold. It is shown that in the case of small yielding, the differential stress intensity factor provides an adequate description of cyclic plastic deformation at the crack tip and correlates well with the crack growth rate. The unzipping model based on crack tip shear decohesion process is found to be in good agreement with the measured crack growth and striation spacing measurements. The proposed model of crack growth threshold gives correct predictions of the crack growth behavior in the near-threshold region.
    Keywords: STRUCTURAL MECHANICS
    Type: In: Mechanics of fatigue; Nov 15, 1981 - Nov 20, 1981; Washington, DC
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  • 100
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    Design and fabrication of brazed Rene 41 honeycomb sandwich structural panels for advanced space transportation systems (1981)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The design and fabrication of two large brazed Rene 41 honeycomb panels, the establishment of a test plan, the design and fabrication of a test fixture to subject the panels to cyclic thermal gradients and mechanical loads equivalent to those imposed on an advanced space transportation vehicle during its boost and entry trajectories are discussed. The panels will be supported at four points, creating three spans. The outer spans are 45.7 cm (18 in.) and the center span 76.2 cm (30 in). Specimen width is 30.5 cm (12 in.). The panels were primarily designed by boost conditions simulated by subjecting the panels to liquid nitrogen, 77K (-320 F) on one side and 455K (360 F) on the other side and by mechanically imposing loads representing vehicle fuel pressure loads. Entry conditions were simulated by radiant heating to 1034K (1400 F). The test program subjected the panels to 500 boost thermal conditions. Results are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165801 , NAS 1.26:165801 , D180-26252-1
    Format: application/pdf
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