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  • Inorganic Chemistry  (739)
  • STRUCTURAL MECHANICS  (254)
  • 2015-2019
  • 1990-1994
  • 1975-1979  (993)
  • 1976  (993)
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  • 2015-2019
  • 1990-1994
  • 1975-1979  (993)
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  • 1
    facet.materialart.
    Unknown
    In:  CASI
    Publication Date: 2006-08-09
    Description: An idealized two-dimensional example of rapid interface flow extension is described. Initially undisturbed dissimilar isotropic, homogeneous, linearly elastic half-spaces are perfectly bonded along the interface y=0. Quantities associated with the half-space or = to 0 are denoted by the prime superscript or the subscripts 3 or 4 while those in y or = to 0 carry the subscripts 1 or 2. At time t=0 adjacent material points at x=0, y= + or - 0 are forced apart horizontally with a constant relative velocity delta v. This results in a zone of bond failure which extends symmetrically along the interface at a constant rate c. The newly created flaw surfaces are in sliding contact resisted by Coulomb friction. The friction coefficient is gamma.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 1; p 239-246
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  • 2
    Publication Date: 2006-08-09
    Description: Based on the two dimensional theory of elasticity and by the use of Muskhelishvili's technique, the influence of a circular hole, under uniform normal pressure, on the stresses around a line crack in an infinite plate subjected to tension is discussed. Numerical calculations were carried out, and the variation of the crack tip stress intensity factor due to the geometry was clarified.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 1; p 275-282
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  • 3
    Publication Date: 2006-08-09
    Description: The effect of subcritical crack growth on the geometry dependence of nonlinear fracture toughness parameters was studied by comparing the toughness values for different specimen geometries at the onset of subcritical crack growth and at the initiation of unstable crack propagation. Center-cracked thin sheet specimens of 2024-T3 and 7075-T6 aluminum alloys were tested by varying the specimen length L, width w, and crack length-to-width ratio c/w. When the onset of unstable crack propagation was selected as the critical point, the nonlinear energy toughness and the R curve toughness increased with increasing w and decreasing L and c/w. However, when the onset of subcritical crack growth was taken as the critical point, energy toughness and the linear toughness values were independent of these geometrical variables.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 1; p 257-266
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  • 4
    Publication Date: 2006-08-09
    Description: The problem to be considered is the sudden appearance of a flaw or crack in a strip of material of finite height subjected to tensile loading. Stress waves are generated within the strip and are reflected from boundary to boundary. Of interest is the maximum value of the dynamic stress intensity factor at a given instance of time as the strip height to crack length ratio is varied.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 1; p 205-214
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  • 5
    Publication Date: 2011-08-17
    Description: An exact three-dimensional analysis of wave propagation in laminated orthotropic circular cylindrical-shells is developed. Numerical results are presented for three-ply shells, and for various axial wave lengths, circumferential wave numbers, and thicknesses. Results from a thin shell theory and a refined approximate theory are compared with the exact results.
    Keywords: STRUCTURAL MECHANICS
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  • 6
    facet.materialart.
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    In:  Other Sources
    Publication Date: 2011-08-17
    Description: Thin-gaged or high toughness materials containing cracks usually fail in a ductile manner with nominal failure stresses approaching the ultimate strength of the material. For such materials, a two-parameter fracture criterion was developed. An equation which related the linear elastic stress-intensity factor, elastic nominal stress, and two material parameters has previously been derived and has been used as a fracture criterion for surface- and through-cracked specimens under tensile loading. In the present paper the two-parameter fracture criterion was rederived in a more general form and was extended to compact and notch-bend fracture specimens. A close correlation was found between experimental and calculated failure stresses.
    Keywords: STRUCTURAL MECHANICS
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  • 7
    Publication Date: 2011-08-17
    Description: By use of the principle of superposition the stiff-flanged shear web is modeled mathematically by an infinite elastic strip with fixed longitudinal edges. The shear-stress intensity factor for a central longitudinal crack is calculated for various values of the ratio of strip width to crack length, h/a, in the range 0.1-10. The interaction of the crack with the boundaries is illustrated by boundary shear-stress distributions for three values of h/a. Some implications of the results for the design of damage-tolerant shear webs are discussed briefly.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 12; Apr. 197
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  • 8
    facet.materialart.
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    In:  Other Sources
    Publication Date: 2011-08-17
    Description: An analytic model is developed to calculate the reliability of a structure after it is inspected for cracks. The model accounts for the growth of undiscovered cracks between inspections and their effect upon the reliability after subsequent inspections. The model is based upon a differential form of Bayes' Theorem for reliability, and upon fracture mechanics for crack growth.
    Keywords: STRUCTURAL MECHANICS
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  • 9
    Publication Date: 2011-08-17
    Description: The fully-stressed design (FSD) appears to be the most widely used approach for sizing of flight structures under strength and minimum-gage constraints. Almost all of the experience with FSD has been with structures primarily under mechanical loading as opposed to thermal loading. In this method the structural sizes are iterated with the step size, depending on the ratio of the total stress to the allowable stress. In this paper, the thermal fully-stressed design (TFSD) procedure developed for problems involving substantial thermal stress is extended to biaxial stress members using a Von Mises failure criterion. The TFSD resizing procedure for uniaxial stress is restated and the new procedure for biaxial stress members is developed. Results are presented for an application of the two procedures to size a simplified wing structure.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 14; Oct. 197
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  • 10
    Publication Date: 2011-08-17
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 49; Dec. 8
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  • 11
    Publication Date: 2011-08-16
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Solids and Structures; 12; 8, 19; 1976
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  • 12
    Publication Date: 2011-08-16
    Description: The Galerkin method is used to investigate the large-amplitude free vibrations of simply supported and clamped tapered beams of rectangular cross-section which are frequently encountered in practical structures. Two types of linear tapers are considered: breadth and depth tapers. Two solutions are obtained for each type of taper, using trigonometric and polynomial displacement distributions. Frequency-amplitude relationships are obtained for all these cases for the fundamental flexural mode. The results indicate good agreement between trigonometric and polynomial solutions for all cases. The nonlinearity is noted to be always of the hardening type and, as expected, it is severe for beams with depth taper as compared with beams with breadth taper.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 14; Feb. 197
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  • 13
    facet.materialart.
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    In:  Other Sources
    Publication Date: 2011-08-16
    Description: Mathematical programming techniques provide a general approach to automated structural design. An iterative method is proposed in which design is treated as a hierarchy of subproblems, one being locally constrained and the other being locally unconstrained. It is assumed that the design space is locally convex in the case of good initial designs and that the objective and constraint functions are continuous, with continuous first derivatives. A general design algorithm is outlined for finding a move direction which will decrease the value of the objective function while maintaining a feasible design. The case of one-dimensional search in a two-variable design space is discussed. Possible applications are discussed. A major feature of the proposed algorithm is its application to problems which are inherently ill-conditioned, such as design of structures for optimum geometry.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering; 10; 3, 19; 1976
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  • 14
    Publication Date: 2011-08-17
    Description: Tests were conducted in a small wind tunnel to study the torsional stall flutter behavior of a two-dimensional flat-plate wing pivoted about the midchord. The nonlinear static divergence equilibrium properties of the wing were well predicted from the measured static moment characteristics. Large amplitude limit cycles ranging from plus or minus 11 degrees to plus or minus 100 degrees were observed. Stall flutter occurred above a critical value of a reduced frequency of about 2. Self-excitation occurred for initial angles of attack between 0 and 8 degrees. Nondimensional harmonic coefficients were extracted from the free transient vibration tests for amplitudes up to 80 degrees.
    Keywords: STRUCTURAL MECHANICS
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  • 15
    facet.materialart.
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    In:  Other Sources
    Publication Date: 2011-08-16
    Description: The problem of the stability of a three-dimensional crack is analyzed within a lattice-statics approximation. The consequence of introducing a jog into the crack face as well as the effects of various nonlinear-force laws are studied. The phenomenon of lattice trapping (upper and lower bounds on the applied stress for an equilibrium crack of given length) is again obtained. It is possible to obtain some physical insight into which aspects of the force law are critical for crack stability. In particular, the inadequacy of a thermodynamic approach - which relates the critical stress to a surface energy corresponding to the area under the cohesive-force-vs-displacement curve - is demonstrated. Surface energy is a global property of the cohesive-force law. Crack stability is sensitive to much more refined aspects of the cohesive-force law. Crack healing is sensitive to the long-range portion of the cohesive force. Crack expansion is sensitive to the position of the maximum in the cohesive-force relation.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Applied Physics; 47; Feb. 197
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  • 16
    Publication Date: 2011-08-16
    Description: Symmetric structure matrices are derived for solving plane strain and axisymmetric problems involving incompressible hyperelastic materials. An infinite hollow cylinder subjected to internal pressure is considered as an example. Displacement and hydrostatic pressure profiles are calculated using the Newton-Raphson iteration technique. The results are in good agreement with the exact curves.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 14; Mar. 197
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  • 17
    facet.materialart.
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    In:  Other Sources
    Publication Date: 2011-08-16
    Description: A general set of finite-element equations is developed for treating the nonlinear dynamic response of membranes consisting of complex nonlinear materials. The approach proposed by Key (1974) for a most complete treatment of the finite-element method to the nonlinear dynamic analysis of solids is used in developing the nonlinear equations of motion for membranes with cubic quadrilateral finite elements. The computations are kept general with respect to material modeling by computing the deformation gradient and requiring a constitutive subroutine to supply the Cauchy stress. An example calculation of the vibration of a square membrane demonstrates the accuracy of the formulation for small deformation theory and shows the nonlinear effect of large deformations.
    Keywords: STRUCTURAL MECHANICS
    Type: American Society of Civil Engineers; Journal
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  • 18
    Publication Date: 2011-08-16
    Description: The paper deals with a method of optimizing harmonically or dynamically excited structures which removes the frequency constraint (that specifies that the structure's first natural frequency of vibration must be greater than the excitation frequency), replaces the displacement constraint by an inequality constraint on the allowable stress and applies finite element approximations to the continuous one-dimensional structures. When the problem is posed in this manner, the feasible design space is disconnected or 'disjoint'. An attempt is made to explain this disjointness by studying the optimal design of a thin-walled cantilevered rod subjected to steady, simple harmonic torsional excitation. The finite element method is applied to the optimization of a harmonically excited structure with an arbitrary number of design variables, with the disjointness of the design space, a complicating factor.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 14; Feb. 197
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  • 19
    Publication Date: 2016-06-07
    Description: A finite element analysis procedure built around the NASTRAN system is assessed. A number of support programs that were either written or modified to interface with NASTRAN and some improvements that were made to NASTRAN itself are noted. Some typical models are analyzed and an actual schedule is followed for constructing and analyzing the models to support a large design program.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center NASTRAN: User's Experiences; p 531-554
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  • 20
    Publication Date: 2016-06-07
    Description: The application of NASTRAN to seismic analysis by considering the example of a nuclear power plant control panel was considered. A modal analysis of a three-dimensional model of the panel, consisting of beam and quadri-lateral membrane elements, is performed. Using the results of this analysis and a typical response spectrum of an earthquake, the seismic response of the structure is obtained. ALTERs required to the program in order to compute the maximum modal responses as well as the resultant response are given. The results are compared with those obtained by using the SAP IV computer program.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center MATRAN: User's Experiences; p 515-530
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  • 21
    Publication Date: 2016-06-07
    Description: The Level 16 flutter analysis capability was applied to an aspect-ratio-6.8 subsonic transport type wing, an aspect-ratio-1.7 arrow wing, and an aspect-ratio-1.3 all movable horizontal tail with a geared elevator. The transport wing and arrow wing results are compared with experimental results obtained in the Langley transonic dynamic tunnel and with other calculated results obtained using subsonic lifting surface (kernel function) unsteady aerodynamic theory.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: User's Experiences; p 495-512
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  • 22
    Publication Date: 2016-06-07
    Description: NASTRAN analysis results are scanned to determine maximum and minimum displacements, forces and stresses. Allowables and margins of safety are computed, and in the case of multiple loading conditions, envelopes for displacements, forces, stresses and margins of safety are also produced for specified element sets. Graphical plots of the reduced or the regular NASTRAN results may be obtained superimposed either of a developed fuselage strip or on a projection of any specified part of the finite element model. The use of the data reduction, post analysis and graphical plotting capabilities provide the analyst with a fast and convenient tool for the study of NASTRAN analysis results and their presentation for project documentation.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center NASTRAN: User's Experiences; p 555-580
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  • 23
    Publication Date: 2016-06-07
    Description: Two plate elements, the linear strain triangular membrane element CTRIM6 and the higher order plate bending element CTRPLT1, were added to NASTRAN Level 16.0. The theoretical formulation, programming details, and bulk data information pertaining to the addition of these elements are discussed. Sample problems illustrating the use of these elements are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center NASTRAN: User's Experiences; p 439-478
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  • 24
    Publication Date: 2016-06-07
    Description: A computer code for the analysis of reinforced concrete structures was developed using NASTRAN as a basis. Nonlinear iteration procedures were developed for obtaining solutions with a wide variety of loading sequences. A direct access file system was used to save results at each load step to restart within the solution module for further analysis. A multi-nested looping capability was implemented to control the iterations and change the loads. The basis for the analysis is a set of mutli-layer plate elements which allow local definition of materials and cracking properties.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center NASTRAN: User's Experiences; p 479-494
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  • 25
    Publication Date: 2016-06-07
    Description: The quadratic isoparametric elements which embody the inverse square root singularity are used for calculating the stress intensity factors at tips of cracks. The strain singularity at a point or an edge is obtained in a simple manner by placing the mid-side nodes at quarter points in the vicinity of the crack tip or an edge. These elements are implemented in NASTRAN as dummy elements. The method eliminates the use of special crack tip elements and in addition, these elements satisfy the constant strain and rigid body modes required for convergence.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center NASTRAN: User's Experiences; p 419-438
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  • 26
    Publication Date: 2016-06-07
    Description: Two NASTRAN models of the Gates Learjet Corporation Model 35/36 Wing were developed. The models and the problems encountered in their development are discussed. A skin buckling analysis used for the ultimate loading conditions is presented. A discussion of the static tests and the correlation of the static test with the NASTRAN results and the results of a supplementary semimonocoque beam analysis are also included.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center NASTRAN: User's Experiences; p 331-352
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  • 27
    Publication Date: 2016-06-07
    Description: The application of NASTRAN to design studies of two very large-area lightweight structures is described. The first is the Satellite Solar Power Station, while the second is a deployable three hundred meter diameter antenna. A brief discussion of the operation of the SSPS is given, followed by a description of the structure. The use of the NASTRAN program for static, vibration and thermal analysis is illustrated and some results are given. Next, the deployable antenna is discussed and the use of NASTRAN for static analysis, buckling analysis and vibration analysis is detailed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center NASTRAN: User's Experiences; p 295-330
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  • 28
    Publication Date: 2016-06-07
    Description: Selected examples are described in which NASTRAN is used as an analysis research tool for composite mechanics and for composite structural components. The examples were selected to illustrate the importance of using NASTRAN as an analysis tool in this rapidly advancing field.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: User's Experiences; p 381-418
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  • 29
    Publication Date: 2016-06-07
    Description: A summary of fluid/structure interaction capabilities for the NASTRAN computer program is presented. Indirect applications of the program towards solving this class of problem were concentrated on. For completeness and comparitive purposes, direct usage of NASTRAN is briefly discussed. The solution technology addresses both steady state and transient dynamic response problems.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center NASTRAN: User's Experiences; p 229-250
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  • 30
    Publication Date: 2016-06-07
    Description: A method is described from which the interaction of an elastic structure with an infinite acoustic fluid is determined. The displacements of the structure and the pressure field of the immediate surrounding fluid are modeled by finite elements, and the remaining pressure field of the infinite fluid region is given by an analytical expression. This method yields a frequency dependent boundary condition for the outer fluid boundary when applied to the frequency response of an elastic beam in contact with an acoustic fluid. The frequency response of the beam is determined using NASTRAN, and compares favorably to the exact solution which is also presented. The effect of the fluid on the response of the structure at low and high frequencies is due to added mass and damping characteristics, respectively.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center NASTRAN: User's Experiences; p 251-272
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  • 31
    Publication Date: 2016-06-07
    Description: Stresses and deformations in thick, short, composite cylinder subjected to axially varying radial pressure are studied. Effect of slippage at the interface is examined. In the NASTRAN finite element model, multipoint constraint feature is utilized. Results are compared with theoretical analysis and SAP-IV computer code. Results from NASTRAN computer code are in good agreement with the analytical solutions. Results suggest a considerable influence of interfacial slippage on the axial bending stresses in the cylinder.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center NASTRAN: User's Experiences; p 161-176
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  • 32
    Publication Date: 2016-06-07
    Description: NASTRAN contains two techniques to solve the differential stiffness problems. One is incorporated in a new static analysis rigid format and the other is contained in a new normal modes analysis rigid format. The two techniques relative to computational accuracy and time of execution are compared.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center NASTRAN: User's Experiences; p 149-160
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  • 33
    Publication Date: 2016-06-07
    Description: A detailed description is given of how the decoupling approximation known as the doubly asymptotic approximation is implemented with NASTRAN to solve shock problems for submerged structures. The general approach involves locating the nonsymmetric terms (which couple structural and fluid variables) on the right hand side of the equations. This approach results in coefficient matrices of acceptable bandwidth but degrades numerical stability, requiring a smaller time step size than would otherwise be used. It is also shown how the structure's added (virtual) mass matrix, is calculated with NASTRAN.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center NASTRAN: User's Experiences; p 207-228
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  • 34
    Publication Date: 2016-06-07
    Description: An overview of four analysis capabilities, which developed and integrated into the NASTRAN Thermal Analyzer, is given. To broaden the scope of applications, these additions provide the NTA users with the following capabilities: (1) simulating a thermal louver as a means of the passive thermal control, (2) simulating a fluid loop for transporting energy as a means of the active thermal control, (3) condensing a large sized finite element model for an efficient transient thermal analysis, and (4) entering multiple boundary condition sets in a single submission for execution in steady state thermal analyses.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: User's Experiences; p 119-126
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  • 35
    Publication Date: 2016-06-07
    Description: Implementation of the tridiagonal reduction method for real eigenvalue extraction in structural vibration and buckling problems is described. The basic concepts underlying the method are summarized and special features, such as the computation of error bounds and default modes of operation are discussed. In addition, the new user information and error messages and optional diagnostic output relating to the tridiagonal reduction method are presented. Some numerical results and initial experiences relating to usage in the NASTRAN environment are provided, including comparisons with other existing NASTRAN eigenvalue methods.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN" User's Experiences; p 127-148
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  • 36
    Publication Date: 2016-06-07
    Description: The NTA Level 15.5.2/3, was used to provide non-linear steady-state (NLSS) and non-linear transient (NLTR) thermal predictions for the International Ultraviolet Explorer (IUE) Scientific Instrument (SI). NASTRAN structural models were used as the basis for the thermal models, which were produced by a straight forward conversion procedure. The accuracy of this technique was sub-sequently demonstrated by a comparison of NTA predicts with the results of a thermal vacuum test of the IUE Engineering Test Unit (ETU). Completion of these tasks was aided by the use of NTA subroutines.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: User's Experiences; p 99-118
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  • 37
    Publication Date: 2016-06-07
    Description: An automated strength sizing capability is described. The technique determines the distribution of material among the elements of a structural model. The sizing is based on either a fully stressed design or a scaled feasible fully stressed design. Results obtained from the application of the strength sizing to the structural sizing of a composite material wing box using material strength allowables are presented. These results demonstrate the rapid convergence of the structural sizes to a usable design.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center NASTRAN: User's Experiences; p 53-66
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  • 38
    Publication Date: 2016-06-07
    Description: Eight alternative modeling techniques to specify prescribed temperature at grid or scalar points for transient thermal analyses are presented. Four cases are for constant temperatures, and the others are time varying temperature functions. Theoretical explications and detailed listing of input data cards used for illustrating different modelings are given. It is shown that the NTA is exploited to extend beyond its normal capabilities through innovative modeling techniques. In addition, the effect of node valency on the energy distribution grid points is illustrated and discussed. Guidelines to delineate this effect are given.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: User's Experiences; p 3-20
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  • 39
    Publication Date: 2016-06-07
    Description: A procedure for the local stiffness modifications of large structures is described. It enables structural modifications without an a priori definition of the changes in the original structure and without loss of efficiency due to multiple loading conditions. The solution procedure, implemented in NASTRAN, involved the decomposed stiffness matrix and the displacement vectors of the original structure. It solves the modified structure exactly, irrespective of the magnitude of the stiffness changes. In order to investigate the efficiency of the present procedure and to test its applicability within a design environment, several real and large structures were solved. The results of the efficiency studies indicate that the break-even point of the procedure varies between 8% and 60% stiffness modifications, depending upon the structure's characteristics and the options employed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center NASTRAN: User's Experiences; p 21-52
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  • 40
    Publication Date: 2016-06-07
    Description: Flat panel flutter at high supersonic Mach number is analyzed using NASTRAN Level 16.0 by means of modifications to the code. Two-dimensional plate theory and quasi-steady aerodynamic theory are employed. The finite element formulation and solution procedure are presented. Modifications to the NASTRAN code are discussed. Convergence characteristics of the iteration processes are also briefly discussed. Effects of aerodynamic damping, boundary support condition and applied in-plane loading are included. Comparison of nonlinear vibration and linear flutter results with analytical solutions demonstrate that excellent accuracy is obtained with NASTRAN.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: User's Experiences; p 67-98
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  • 41
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    In:  CASI
    Publication Date: 2016-06-07
    Description: Improvements in the NASTRAN systems management office are presented. Among the improvements are the following items: (1) the FEER eigenmethod and its extension to complete eigenvalue problems; (2) the addition of a supersonic flutter package which allows gust response calculations and active control effects as membrane In addition to capabilities mentioned, an error correction information system is also introduced.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: User's Experiences; p 1-2
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  • 42
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    In:  CASI
    Publication Date: 2016-06-07
    Description: A flight program to measure atmospheric turbulence at high altitudes (long wavelengths) in a variety of meteorological conditions is described and some results obtained in high altitude wind shear are discussed. Results are also presented from wind tunnel test programs to measure fluctuating pressures associated with over-the-wing configurations. A flexible aircraft take off and landing analysis and an active control landing gear analysis, are developed and their capabilities are described. Efforts to validate these analyses with experimental data are also discussed as well as results obtained from parametric studies.
    Keywords: STRUCTURAL MECHANICS
    Type: Proc. of the SCAR Conf., Pt. 2,; 22 p
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  • 43
    Publication Date: 2016-06-07
    Description: The lower part of the atmospheric boundary layer (strong wind conditions) was simulated in low speed wind tunnel for the modeling of wind loads on low-rise structures. The turbulence characteristics of the turbulent boundary layer in the wind tunnel are compared with full scale measurements and with measurements made at NASA Wallops Flight Center. Wind pressures measured on roofs of a 1:70 scale model of a small single family dwelling were compared with results obtained from full scale measurements. The results indicate a favorable comparison between full scale and model pressure data as far as mean, r.m.s. and peak pressures are concerned. In addition, results also indicate that proper modeling of the turbulence is essential for proper simulation of the wind pressures.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 3; p 1167-1176
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  • 44
    Publication Date: 2016-06-07
    Description: The radiation of sound from vibrating cylindrical beams is analyzed based on the frequency of the beam vibrations and the physical characteristics of the beam and its surroundings. A statistical analysis of random beam vibrations allows this result to be independent of the boundary conditions at the ends of the beam. The acoustic power radiated by the beam can be determined from a knowledge of the frequency band vibration data without a knowledge of the individual modal vibration amplitudes. A practical example of the usefulness of this technique is provided by the application of the theoretical calculations to the prediction of the octave band acoustic power output of the picking sticks of an automatic textile loom. Calculations are made of the expected octave band sound pressure levels based on measured acceleration data. These theoretical levels are subsequently compared with actual sound pressure level measurements of loom noise.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 3; p 1071-1081
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  • 45
    facet.materialart.
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    In:  CASI
    Publication Date: 2016-06-07
    Description: Theoretical and experimental research on structural-acoustic interaction is reviewed. The emphasis is upon the radiation from and acoustic loading of baffled rectangular plates and membranes. The topics discussed include a criterion for strong radiation loading, the mass law for a finite panel, numerical calculation of the radiation impedance of a finite panel in the presence of a parallel mean flow, and experimental determination of the effect of vibration amplitude and Mach number upon panel radiation efficiency.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 3; p 1043-1055
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  • 46
    Publication Date: 2016-06-07
    Description: Theories regarding the radiation of sound are reviewed and the implementation in strategies for explaining or measuring the sound produced by practical strucutres are discussed. Particular attention is given to those aspects that relate to the determination of the relative amounts of sound generated by various parts of a machine or structure, which can be very useful information for noise reduction efforts.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 3; p 1031-1042
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  • 47
    Publication Date: 2016-06-07
    Description: Stress concentration factors around a circular hole in a composite laminate are determined. The specific case investigated is a four layer (-45/45/45/-45 degs) graphite epoxy laminate. The factors are determined experimentally by means of electrical resistance strain gages, and analytically by using a hybrid finite element analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 711-720
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  • 48
    Publication Date: 2016-06-07
    Description: The contour integral method is extended to general boundary value problems involving imperfect bonding of dissimilar materials. The loading and restraints are shown to have a significant effect on the stress intensity. Example problems are presented to illustrate the results.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 699-709
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  • 49
    facet.materialart.
    Unknown
    In:  CASI
    Publication Date: 2016-06-07
    Description: By using Galerkin's variational method an approximate solution is developed for a system of two differential equations with linear partial derivatives of the second order. This system of differential equations corresponds to the physical model, known in the literature as the Timoshenko Beam. The results obtained are applied to two particular cases representing respectively: the case of a beam with a rectangular section, with a constant height and a basis with a linear variation; and the case of a beam with a constant basis and a height with cubic variation.
    Keywords: STRUCTURAL MECHANICS
    Type: Advan. in Eng. Sci., Vol. 2; p 671-685
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  • 50
    facet.materialart.
    Unknown
    In:  CASI
    Publication Date: 2016-06-07
    Description: Elastic bodies or systems may not require external energy for certain finite and continuous deformations. Conditions providing these kinds of effortless, or neutral, deformations are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 665-670
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  • 51
    Publication Date: 2016-06-07
    Description: Rayleigh-Ritz and modified Rayleigh-Ritz procedures are used to construct approximate solutions for the response of a thick-walled sphere to uniform pressure loads and an arbitrary radial temperature distribution. The thermoelastic properties of the sphere are assumed to be transversely isotropic and nonhomogeneous; variations in the elastic stiffness and thermal expansion coefficients are taken to be an arbitrary function of the radial coordinate and temperature. Numerical examples are presented which illustrate the effect of the temperature-dependence upon the thermal stress field. A comparison of the approximate solutions with a finite element analysis indicates that Ritz methods offer a simple, efficient, and relatively accurate approach to the problem.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 639-651
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  • 52
    facet.materialart.
    Unknown
    In:  CASI
    Publication Date: 2016-06-07
    Description: Dynamic plastic response of a thin cylindrical shell, immersed in a potential fluid initially at rest and subjected to internal pressure pulse of arbitrary shape and duration, is examined. The shell is assumed to respond as a rigid-perfectly plastic material while the fluid is taken as inviscid and incompressible. The fluid back pressure is incorporated into the equation of motion of the shell as an added mass term. Since arbitrary pulses can be reduced to equivalent rectangular pulses, the equation of motion is solved only for a rectangular pulse. The influence of the fluid in reducing the final plastic deformation is demonstrated by a numerical example.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 627-637
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  • 53
    Publication Date: 2016-06-07
    Description: Large deflections of a shallow elastic conical membrane fixed at the outer edge and loaded by either uniform or hydrostatic pressure are investigated. The overning equations were solved by the method of matched asymptotic expansions and by a finite difference method. Agreement between the two methods was excellent for the small values of the perturbation parameter.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 575-584
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  • 54
    Publication Date: 2016-06-07
    Description: The response of a thin, rigid, viscoplastic plate subjected to a spatially axisymmetric Gaussian ideal impulse loading was studied analytically. The Gaussian ideal impulse distribution instantaneously imparts a Gaussian initial velocity distribution to the plate, except at the fixed boundary. The plate deforms with monotonically increasing deflections until the initial dynamic energy is completely dissipated in plastic work. The simply supported plate of uniform thickness obeys the von Mises yield criterion and a generalized constitutive equation for rigid, viscoplastic materials. For the small deflection bending response of the plate, neglecting the transverse shear stress in the yield condition and rotary inertia in the equations of dynamic equilibrium, the governing system of equations is essentially nonlinear. A proportional loading technique, known to give excellent approximations of the exact solution for the uniform load case, was used to linearize the problem and obtain analytical solution in the form of eigenvalue expansions. The linearized governing equations required the knowledge of the collapse load of the corresponding static problem.
    Keywords: STRUCTURAL MECHANICS
    Type: Advan. in Eng. Sci., Vol. 2; p 595-616
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  • 55
    Publication Date: 2016-06-07
    Description: The Display and Edit (D and E) Module described is one of six major modules being developed for the STAGING (STructural Analysis through Generalized INteractive Graphics) System. Several remarks are included concerning the computer environment and the architecture of the data base. The utility of this module is emphasized.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 543-553
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  • 56
    Publication Date: 2016-06-07
    Description: An algorithm for optimal design is given which incorporates several of the desirable features of both mathematical programming and optimality criteria, while avoiding some of the undesirable features. The algorithm proceeds by approaching the optimal solution through the solutions of an associated set of constrained optimal design problems. The solutions of the constrained problems are recognized at each stage through the application of optimality criteria based on energy concepts. Two examples are described in which the optimal member size and layout of a truss is predicted, given the joint locations and loads.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 521-530
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  • 57
    Publication Date: 2016-06-07
    Description: The fundamental frequency of vibration of an Euler-Bernoulli or a Timoshenko beam of a specified constant volume is maximized subject to the constraint that under a prescribed loading the maximum stress or maximum deflection at any point along the beam axis will not exceed a specified value. In contrast with the inequality constraint which controls the minimum cross-section, the present inequality constraints lead to more meaningful designs. The inequality constraint on stresses is as easily implemented as the minimum cross-section constraint but the inequality constraint on deflection uses a treatment which is an extension of the matrix partitioning technique of prescribing displacements in finite element analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 509-519
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  • 58
    facet.materialart.
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    In:  CASI
    Publication Date: 2016-06-07
    Description: After buckling, statically indeterminate trusses, beams, and other strictly symmetric structures may collapse under loads which reach limiting magnitudes. Optimal design is discussed for prescribed values of these collapse loads.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 501-508
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  • 59
    Publication Date: 2016-06-07
    Description: Variational theorems are presented for a theory of small motions superimposed on large static deformations and governing equations for prestressed beams on the basis of 3-D theory of elastodynamics. First, the principle of virtual work is modified through Friedrichs's transformation so as to describe the initial stress problem of elastodynamics. Next, the modified principle together with a chosen displacement field is used to derive a set of 1-D macroscopic governing equations of prestressed beams. The resulting equations describe all the types of superimposed motions in elastic beams, and they include all the effects of transverse shear and normal strains, and the rotatory inertia. The instability of the governing equations is discussed briefly.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 481-490
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  • 60
    Publication Date: 2016-06-07
    Description: An equation describing the radial displacement in a k layered anisotropic cylinder was obtained. The cylinders are initially unstressed but are subjected to either a time dependent normal stress or a displacement at the external boundaries of the laminate. The solution is obtained by utilizing the Vodicka orthogonalization technique. Numerical examples are given to illustrate the procedure.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 459-472
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  • 61
    Publication Date: 2016-06-07
    Description: Results are presented for an analysis of the response of long, flexible cantilever beams to applied root rotational accelerations. Maximum values of deformation, slope, bending moment, and shear are found as a function of magnitude and duration of acceleration input. Effects of tip mass and its eccentricity and rotatory inertia on the response are also investigated. It is shown that flexible beams can withstand large root accelerations provided the period of applied acceleration can be kept small relative to the beam fundamental period.
    Keywords: STRUCTURAL MECHANICS
    Type: Advan. in Eng. Sci., Vol. 2; p 491-499
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  • 62
    Publication Date: 2016-06-07
    Description: The effect of finite deformation upon a rotating, orthotropic cylinder was investigated using a general incremental theory. The incremental equations of motion are developed using the variational principle. The governing equations are derived using the principle of virtual work for a body with initial stress. The governing equations are reduced to those for the title problem and a numerical solution is obtained using finite difference approximations. Since the problem is defined in terms of one independent space coordinate, the finite difference grid can be modified as the incremental deformation occurs without serious numerical difficulties. The nonlinear problem is solved incrementally by totaling a series of linear solutions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 473-480
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  • 63
    Publication Date: 2016-06-07
    Description: The endochronic theory of plasticity originated by Valanis was applied to study the axially symmetric motion of circular cylindrical thick shells subjected to an arbitrary pressure transient applied at its inner surface. The constitutive equations for the thick shells were obtained. The governing equations are solved by means of the nearcharacteristics method.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 449-458
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  • 64
    Publication Date: 2016-06-07
    Description: The free vibrations are studied of laminated anisotropic elliptic plates with clamped edges. The analytical formulation is based on a Mindlin-Reissner type plate theory with the effects of transverse shear deformation, rotary inertia, and bending-extensional coupling included. The frequencies and mode shapes are obtained by using the Rayleigh-Ritz technique in conjunction with Hamilton's principle. A computerized symbolic integration approach is used to develop analytic expressions for the stiffness and mass coefficients and is shown to be particularly useful in evaluating the derivatives of the eigenvalues with respect to certain geometric and material parameters. Numerical results are presented for the case of angle-ply composite plates with skew-symmetric lamination.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 425-438
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  • 65
    Publication Date: 2016-06-07
    Description: The effects which moderately large deflections have on the frequency spectrum of rotating rings and cylinders are considered. To develop the requisite solution, a variationally constrained version of the Lindstedt-Poincare procedure is employed. Based on the solution developed, in addition to considering the effects of displacement induced nonlinearity, the role of Coriolis forces is also given special consideration.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 409-416
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  • 66
    Publication Date: 2016-06-07
    Description: Stability in energy for the Newmark beta-family of time integration operators for nonlinear material problems is examined. It is shown that the necessary and sufficient conditions for unconditional stability are equivalent to those predicted by Fourier methods for linear problems.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 2; p 385-391
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  • 67
    Publication Date: 2019-06-27
    Description: The subject considered is the stress and deformation fields in a cracked elastic-plastic power law hardening material under plane strain tensile loading. An incremental plasticity finite element formulation is developed for accurate analysis of the complete field problem including the extensively deformed near tip region, the elastic-plastic region, and the remote elastic region. The formulation has general applicability and was used to solve the small scale yielding problem for a set of material hardening exponents. Distributions of stress, strain, and crack opening displacement at the crack tip and through the elastic-plastic zone are presented as a function of the elastic stress intensity factor and material properties.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 76-MAT-O
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  • 68
    Publication Date: 2019-06-27
    Description: An expression is obtained for the first derivatives with respect to the sizing variables of a statically reduced stiffness matrix that is a nonlinear function of the sizing variables, where the unreduced stiffness matrix is a linear function of the sizing variables. An accepted procedure to reduce the number of degrees of freedom is to eliminate a number of nodal displacements from the degrees of freedom such that the accuracy of the flutter analysis is not significantly affected. In a typical optimization procedure with flutter constraints, the derivative of the stiffness matrix may be used in a form that contains the characteristic vector of the flutter matrix equation and the transpose of the characteristic vector of the adjoint flutter matrix equation corresponding to a particular solution of the flutter equation.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Aircraft; 13; Jan. 197
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  • 69
    Publication Date: 2019-06-27
    Description: The paper proves convergence of an iterative procedure for calculating the deflections of built-up component structures which can be represented as consisting of a dominant, relatively stiff primary structure and a less stiff secondary structure, which may be composed of one or more substructures that are not connected to one another but are all connected to the primary structure. The iteration consists in estimating the deformation of the primary structure in the absence of the secondary structure on the assumption that all mechanical loads are applied directly to the primary structure. The j-th iterate primary structure deflections at the interface are imposed on the secondary structure, and the boundary loads required to produce these deflections are computed. The cycle is completed by applying the interface reaction to the primary structure and computing its updated deflections. It is shown that the mathematical condition for convergence of this procedure is that the maximum eigenvalue of the equation relating primary-structure deflection to imposed secondary-structure deflection be less than unity, which is shown to correspond with the physical requirement that the secondary structure be more flexible at the interface boundary.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 14; Jan. 197
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  • 70
    Publication Date: 2019-06-27
    Description: In this paper the fracture problem of a composite plate which consists of perfectly bonded parallel load carrying laminates and buffer strips is considered. It is assumed that the fatigue cracks may appear and spread in main laminates or in buffer strips or in both perpendicular to the interfaces. The external load is applied to the plate parallel to the strips and away from the crack region. The problem is solved for fully imbedded cracks and for broken laminates or strips and the corresponding stress intensity factors are calculated.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 12; Feb. 197
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  • 71
    Publication Date: 2019-06-27
    Description: A numerical solution to the three-dimensional equations of elasticity is presented for the problem of a semi-elliptical surface crack in the surface of a finite thickness solid. The alternating method is used to develop the numerical results which incorporate the effects on the stress intensity factor due to the presence of both the front and the back surfaces. The stress intensity factor is presented as a function of position along the crack border for a variety of crack shapes and crack depths. A comparison of the results of this study is made with previous theoretical and experimental work.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 12; Feb. 197
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  • 72
    facet.materialart.
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    In:  Other Sources
    Publication Date: 2019-06-27
    Description: The paper deals with the plane elastostatic contact problem for an infinite elastic wedge of arbitrary angle. The medium is loaded through a frictionless rigid wedge of a given symmetric profile. Using the Mellin transform formulation the mixed boundary value problem is reduced to a singular integral equation with the contact stress as the unknown function. With the application of the results to the fracture of the medium in mind, the main emphasis in the study has been on the investigation of the singular nature of the stress state around the apex of the wedge and on the determination of the contact pressure.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Elasticity; 6; Jan. 197
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  • 73
    Publication Date: 2019-06-27
    Description: Several intact or broken stringers which are continuously attached to a cracked orthotropic sheet through an adhesive are considered. The effect of orthotropy on the stress intensity factors is investigated. The stringers are assumed to be partially debonded due to high stress concentrations. The shear stress distribution between the stringers and the plate and the stress intensity factors are obtained from an integral equation which represents the continuity of displacements along the bond lines.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-148601
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  • 74
    Publication Date: 2019-06-27
    Description: Methods are presented for calculating design limit loads compatible with probabilistic structural design criteria. The approach is based on the concept that the desired limit load, defined as the largest load occurring in a mission, is a random variable having a specific probability distribution which may be determined from extreme-value theory. The design limit load, defined as a particular of this random limit load, is the value conventionally used in structural design. Methods are presented for determining the limit load probability distributions from both time-domain and frequency-domain dynamic load simulations. Numerical demonstrations of the method are also presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-149939 , D180-19275-1
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  • 75
    Publication Date: 2019-06-27
    Description: A two dimensional orthotropic sheet with through-the-thickness cracks and temperature gradient was analyzed. The program includes special crack tip elements that account for singular stress fields associated with crack opening and crack sliding displacements at the crack tip. The program also includes a linear spring element and a constant strain, triangular element. A number of problems for which closed form solutions exist were analyzed to demonstrate the capabilities of the program.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-2698
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  • 76
    Publication Date: 2019-06-27
    Description: A previously developed fracture criterion was applied to fracture data for surface-cracked specimens subjected to remote tensile loading and for specimens with a corner crack (or cracks) emanating from a circular hole subjected to either remote tensile loading or pin loading in the hole. The failure stresses calculated from this criterion were consistent with experimental failure stresses for both surface and corner cracks for a wide range of crack shapes and crack sizes in specimens of aluminum alloy, titanium alloy, and steel. Empirical equations for the elastic stress-intensity factors for a surface crack and for a corner crack (or cracks) emanating from a circular hole in a finite-thickness and finite-width specimen were also developed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-8244 , L-10203
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  • 77
    Publication Date: 2019-06-27
    Description: An engineering procedure is presented for calculating the compressive buckling strength of isogrid cylinders using shell of revolution techniques and accounting for loading beyond the material proportional limit and/or local buckling of the skin prior to general buckling. A general nondimensional chart is presented which can be used in conjunction with formulas based on simple deformation plasticity theory to calculate postbuckling stiffnesses of the skin. The stiffening grid system is treated as an equivalent isotropic grid layer. Stiffnesses are determined for this grid layer, when loaded beyond the proportional limit, by the same plasticity theory used for the skin and a nonlinear stress-strain curve constructed from simple isogrid-handbook formulas and standard-reference-manual stress-strain curves for the material involved. Comparison of prebuckling strains and buckling results obtained by this procedure with data from a large isogrid-cylinder test is excellent with the calculated buckling load no more than 4 percent greater than the test value.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-8239 , L-10860
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  • 78
    Publication Date: 2019-06-27
    Description: The theoretical crack-opening displacements for center-crack, compact, and crack-line wedge-loaded specimens (reported in the ASTM Proposed Recommended Practice for R-Curve Determination (1974)) disagree with experimental measurements in the literature. The disagreement is a result of using approximate specimen configurations and load representation to obtain the theoretical displacements. An improved method of boundary collocation is presented which was used to obtain the theoretical displacements in these three specimen types; the actual specimen configurations and more accurate load representation were used. In the analysis of crack-opening displacements in the compact and crack-line wedge-loaded specimens, the effects of the pin-loaded holes were also included. The theoretical calculations agree with the experimental measurements reported in the literature. Also examined are accurate polynomial expressions for crack-opening displacements in both compact and crack-line wedge-loaded specimens.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-8268 , L-10829
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  • 79
    Publication Date: 2019-06-27
    Description: The effects of active controls on flutter suppression and gust alleviation of the Arava twin turboprop STOL transport and the Westwind twinjet business transport are investigated. The active control surfaces are introduced in pairs which include, in any chosen wing strip, a 20-percent chord leading-edge control and a 20-percent chord trailing-edge control. Each control surface is driven by a combined linear-rotational sensor system located on the activated strip. The control law is based on the concept of aerodynamic energy and utilizes previously optimized control law parameters based on two-dimensional aerodynamic theory. The best locations of the activated system along the span of the wing are determined for bending-moment alleviation, reduction in fuselage accelerations, and flutter suppression. The effectiveness of the activated system over a wide range of maximum control deflections is also determined. Two control laws are investigated. The first control law utilizes both rigid-body and elastic contributions of the motion. The second control law employs primarily the elastic contribution of the wing and leads to large increases in the activated control effectiveness as compared with the basic control law. The results indicate that flutter speed can be significantly increased (over 70 percent increase) and that the bending moment due to gust loading can be almost totally eliminated by a control system of about 10 to 20 percent span with reasonable control-surface rotations.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-8212 , L-10738
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  • 80
    Publication Date: 2019-06-27
    Description: Extensions developed at Langley Research Center to the VIPASA computer program are described including a procedure for simple thermal stress analysis and options for graphical display of output. Input requirements for operation of the modified program are given in detail.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-73914
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  • 81
    Publication Date: 2019-06-27
    Description: The program documentation and user's guide for the ACCESS-1 computer program is presented. ACCESS-1 is a research oriented program which implements a collection of approximation concepts to achieve excellent efficiency in structural synthesis. The finite element method is used for structural analysis and general mathematical programming algorithms are applied in the design optimization procedure. Implementation of the computer program, preparation of input data and basic program structure are described, and three illustrative examples are given.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-144905
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  • 82
    Publication Date: 2019-06-27
    Description: An explanation is presented of the function of each finite element subroutine in the FORMA library. Example problems are given in some cases to clarify the operations performed by a subroutine.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-144323 , MCR-76-217-VOL-3C
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  • 83
    Publication Date: 2019-06-27
    Description: An explanation of the function of each sparse subroutine in the FORMA library is presented. Example problems are given in some cases to clarify the operations performed by a subroutine.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-144322 , MCR-76-217-VOL-3B
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  • 84
    Publication Date: 2019-06-27
    Description: An explanation is presented of the function of each dense subroutine in the FORMA library. Example problems are given in some cases to clarify the operations performed by a subroutine.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-144321 , MCR-76-217-VOL-3A
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  • 85
    Publication Date: 2019-06-27
    Description: A listing of the source deck of each finite element FORMA subroutine is given to remove the 'black-box' aura of the subroutines so that the analyst may better understand the detailed operations of each subroutine. The FORTRAN 4 programming language is used in all finite element FORMA subroutines.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-144320 , MCR-76-217-VOL-2C
    Format: application/pdf
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  • 86
    Publication Date: 2019-06-27
    Description: A listing of the source deck of each sparse FORMA subroutine is given to remove the 'black-box' aura of the subroutines so that the analyst may better understand the detailed operations of each subroutine. The format of a sparse matrix on a utility tape is also presented. The FORTRAN 4 programming language is used in all sparse FORMA subroutines.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-144319 , MCR-76-217-VOL-2B
    Format: application/pdf
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  • 87
    Publication Date: 2019-06-27
    Description: A listing of the source deck of each dense FORMA subroutine is given to remove the 'black-box' aura of the subroutines so that the analyst may better understand the detail operations of each subroutine. The FORTRAN 4 programming language is used throughout.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-144318 , MCR-76-217-VOL-2A
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  • 88
    Publication Date: 2019-06-27
    Description: Techniques are presented for the solution of structural dynamic systems on an electronic digital computer using FORMA (FORTRAN Matrix Analysis). FORMA is a library of subroutines coded in FORTRAN 4 for the efficient solution of structural dynamics problems. These subroutines are in the form of building blocks that can be put together to solve a large variety of structural dynamics problems. The obvious advantage of the building block approach is that programming and checkout time are limited to that required for putting the blocks together in the proper order.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-144317 , MCR-76-217-VOL-1
    Format: application/pdf
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  • 89
    Publication Date: 2019-06-27
    Description: A study was made of the feasibility of a room-temperature scheme of accelerating fatigue tests for Mach 3 advanced supersonic transport aircraft. The test scheme used equivalent room-temperature cycles calculated for supersonic flight conditions. Verification tests were conducted using specimens representing titanium wing lower surface structure. Test-acceleration parameters were developed for the test with an auxiliary test set. Five specimens were tested with a flight-by-flight load and temperature spectrum to simulate typical Mach 3 operation. Two additional sets of five specimens were tested at room temperature to evaluate the test-acceleration scheme. The fatigue behavior of the specimens generally correlated well with the proposed correction method.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-2658 , D6-42768
    Format: application/pdf
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  • 90
    Publication Date: 2019-06-27
    Description: A detailed analytical study was made to investigate the effects of fuselage cross section (circular and elliptical) and the structural arrangement (integral and nonintegral tanks) on aircraft performance. The vehicle was a 200 passenger, liquid hydrogen fueled Mach 6 transport designed to meet a range goal of 9.26 Mn (5000 NM). A variety of trade studies were conducted in the area of configuration arrangement, structural design, and active cooling design in order to maximize the performance of each of three point design aircraft: (1) circular wing-body with nonintegral tanks, (2) circular wing-body with integral tanks and (3) elliptical blended wing-body with integral tanks. Aircraft range and weight were used as the basis for comparison. The resulting design and performance characteristics show that the blended body integral tank aircraft weights the least and has the greatest range capability, however, producibility and maintainability factors favor nonintegral tank concepts.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-2651
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  • 91
    Publication Date: 2019-06-27
    Description: The technology and data base necessary for sound technical decisions regarding long haul supersonic cruise aircraft transportation systems are considered. The objectives and status of the research elements in the structures and materials program phase of the program are reviewed. Emphasis is placed on reductions in structural mass by research on advanced structural concepts, light-weight materials, improved loads, aeroelastic predictive techniques, and by development of efficient structural design procedures.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-72790
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  • 92
    Publication Date: 2019-06-27
    Description: A FORTRAN program is presented for preliminary analysis and design of multilayered composite panels subjected to inplane loads. All plys are of the same material. The composite is assumed symmetric about the midplane, but need not be balanced. Failure criterion includes limit ply strains and lower bounds on composite inplane stiffnesses. Multiple load conditions are considered. The required input data is defined and examples are provided to aid the use in making the program operational. Average panel design times are two seconds on an IBM 360/67 computer. Results are compared with published literature. A complete FORTRAN listing of program COMAND is provided. In addition, the optimization program CONMIN is required for design.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-73104 , A-6435
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  • 93
    Publication Date: 2019-06-27
    Description: The future requirements for large space structures were examined and the foundation for long range planning of technology development for such structures is provided. Attention is concentrated on a period after 1985 for actual use. Basic ground rule of the study was that applications be of significant importance and have promise of direct economic benefit to mankind. The inputs to the study came from visits to a large number of government and industrial organizations, written studies in current literature, and approximate analyses of potential applications. The paper identifies diverse space applications for large area structures in three general categories: (1) large surfaces for power, (2) large antenna to receive and transmit energy over the radio frequency bandwidth, and (3) space platforms to provide area for general utilizations.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-2621
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  • 94
    Publication Date: 2019-06-27
    Description: Minimum mass honeycomb sandwich panels were sized for transmitting a concentrated load to a uniform reaction through various distances. The form skin gages were fully stressed with a finite element computer code. The panel general stability was evaluated with a buckling computer code labeled STAGS-B. Two skin materials were considered; aluminum and graphite-epoxy. The core was constant thickness aluminum honeycomb. Various panel sizes and load levels were considered. The computer generated data were generalized to allow preliminary least mass panel designs for a wide range of panel sizes and load intensities. An assessment of panel fabrication cost was also conducted. Various comparisons between panel mass, panel size, panel loading, and panel cost are presented in both tabular and graphical form.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-144915 , D6-42680
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  • 95
    Publication Date: 2019-06-27
    Description: It is shown that efficient structural synthesis capabilities can be created by using approximation concepts to mesh finite element structural analysis methods with nonlinear mathematical programming techniques. The history of the application of mathematical programming techniques to structural design optimization problems is reviewed. Several rather general approximation concepts are described along with the technical foundations of the ACCESS 1 computer program, which implements several approximation concepts. A substantial collection of structural design problems involving truss and idealized wing structures is presented. It is concluded that since the basic ideas employed in creating the ACCESS 1 program are rather general, its successful development supports the contention that the introduction of approximation concepts will lead to the emergence of a new generation of practical and efficient, large scale, structural synthesis capabilities in which finite element analysis methods and mathematical programming algorithms will play a central role.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-2552
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  • 96
    Publication Date: 2019-06-27
    Description: An algorithm is reported for resizing structures subjected to combined thermal and mechanical loading. The algorithm is applicable to uniaxial stress elements (rods) and membrane biaxial stress members. Thermal Fully Stressed Design (TFSD) is based on the basic difference between mechanical and thermal stresses in their response to resizing. The TFSD technique is found to converge in fewer iterations than ordinary fully stressed design for problems where thermal stresses are comparable to the mechanical stresses. The improved convergence is demonstrated by example with a study of a simplified wing structure, built-up with rods and membranes and subjected to a combination of mechanical loads and a three dimensional temperature distribution.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-72816
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  • 97
    Publication Date: 2019-06-27
    Description: Cyclic debonding rates were measured during constant-amplitude loading of specimens made of graphite/epoxy bonded to aluminum and S-glass/epoxy bonded to aluminum. Both room-temperature and elevated-temperature curing adhesives were used. Debonding was monitored with a photoelastic coating technique. The debonding rates were compared with three expressions for strain-energy release rate calculated in terms of the maximum stress, stress range, or a combination of the two. The debonding rates were influenced by both adherent thickness and the cyclic stress ratio. For a given value of maximum stress, lower stress ratios and thicker specimens produced faster debonding. Microscopic examination of the debonded surfaces showed different failure mechanisms both for identical adherends bonded with different adhesive and, indeed, even for different adherends bonded with identical adhesives. The expressions for strain-energy release rate correlated the data for different specimen thicknesses and stress ratios quite well for each material system, but the form of the best correlating expression varied among material systems. Empirical correlating expressions applicable to one material system may not be appropriate for another system.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-8126 , L-10480
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  • 98
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    Unknown
    In:  CASI
    Publication Date: 2019-06-27
    Description: The user's manual is restricted to those items related to the use of NASTRAN that are independent of the computing system being used. The features of NASTRAN described include: (1) procedures for defining and loading a structural model and a functional reference for every card that is used for structural modeling; (2) the NASTRAN data deck, including the details for each of the data cards; (3) the NASTRAN control cards that are associated with the use of the program; (4) rigid format procedures, along with specific instructions for the use of each rigid format: (5) procedures for using instructions for the use of each rigid format; (5) procedures for using the NASTRAN plotting capability; (6) procedures governing the creation of DMAP programs; and (7) the NASTRAN diagnostic messages. The NASTRAN dictionary of mnemonics, acronyms, phrases, and other commonly used NASTRAN terms is included along with a limited number of sample problems.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-SP-222(03)
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  • 99
    Publication Date: 2019-06-27
    Description: The elastostatic axisymmetric problem for a long thick-walled cylinder containing a ring-shaped internal or edge crack is considered. Using the standard transform technique the problem is formulated in terms of an integral equation which has a simple Cauchy kernel for the internal crack and a generalized Cauchy kernel for the edge crack as the dominant part. As examples the uniform axial load and the steady-state thermal stress problems have been solved and the related stress intensity factors have been calculated. Among other findings the results show that in the cylinder under uniform axial stress containing an internal crack the stress intensity factor at the inner tip is always greater than that at the outer tip for equal net ligament thicknesses and in the cylinder with an edge crack which is under a state of thermal stress the stress intensity factor is a decreasing function of the crack depth, tending to zero as the crack depth approaches the wall thickness.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-145266
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  • 100
    Publication Date: 2019-06-27
    Description: For abstract, see N76-33552.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-73957-7
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