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  • STRUCTURAL MECHANICS  (603)
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  • 2025-2025
  • 1980-1984  (277)
  • 1970-1974  (325)
  • 1955-1959  (1)
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  • 1
    Publication Date: 2006-03-28
    Description: Cybernetics diagnostics of machines and mechanisms using the spectral approach is discussed. The problem of establishing the accuracy of determination of the spectral composition is investigated. In systems with rectilinear or rotary movement, the vibrations appear in the form of movement rate vibrations, which are equivalent to frequency modulation of the signal, in proportion to the mean movement rate of the body. The case of a harmonic signal which reproduces and analyzes the characteristics of the frequency modulated signal is discussed. Mathematical models are developed to show the relationships of the parameters.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 275-278
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  • 2
    Publication Date: 2006-03-28
    Description: Free vibrations of a system and vibrations which are multiples of them in frequency are discussed. The corresponding periodic forced vibrations of the type n/m (n is the number of periods of disturbance between periods of movement and m is the number of periods of movement in one period of disturbance), generated by a harmonic or close to harmonic disturbance, are propagated close to the corresponding curves of the free vibrations and their frequency multiples. It has been proposed that investigation of transitional modes of motion and capture regions be carried out by precise methods in phase space, with the least number of coordinates. Thus, for example, for nonautonomous second order equations (for example, the Duffing equations), in place of three variables (coordinates, velocity, phases), it is proposed to use two: velocity during transition of the coordinate through zero and phase.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 256-259
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  • 3
    Publication Date: 2006-03-28
    Description: A numerical analysis of the transitional modes of motion for a vibroshock system was conducted. The capture regions of the system are emphasized. The three initial parameters for a nonautonomous vibroshock system with one degree of freedom are identified as: (1) coordinates, (2) velocity, and (3) time. Mathematical models are developed to show the relationship of the parameters. Graphs are included to show the nature of the capture regions and to portray the trajectory of motion of mass with time, by solution of differential equations during increase and decrease in time.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 250-255
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  • 4
    Publication Date: 2006-03-28
    Description: A solution is given to the problem of a transient vibration process in a fastened plate, during a sudden displacement of the edge. Some partial cases of excitation are examined in which the packing can be calculated and the explicit type of change in a deformation over time can be found. Some examples are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 204-207
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  • 5
    Publication Date: 2006-03-28
    Description: The method of automatic identification of acoustical signals, by means of the segmentation was used to investigate noises and vibrations in machines and mechanisms, for cybernetic diagnostics. The structural analysis consists of presentation of a noise or vibroacoustical signal as a sequence of segments, determined by the time quantization, in which each segment is characterized by specific spectral characteristics. The structural spectrum is plotted as a histogram of the segments, also as a relation of the probability density of appearance of a segment to the segment type. It is assumed that the conditions of ergodic processes are maintained.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 179-180
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  • 6
    Publication Date: 2006-03-28
    Description: An experimental investigation for estimating the nonlinearity of a diagnostic object was carried out on a single-stage, spur gear reducer. The linearity of the properties of spur gearing (including the linearity of its mode of operation) was tested. Torsional vibrations of the driven wheel and transverse (to the meshing plane) vibrations of the drive wheel on its support were taken as the two outputs of the object to be analyzed. The results of the investigation showed that the degree of nonlinearity of a reducing gear is essentially connected with its operating mode, so that different mathematical models of it can correspond to different values of the system parameters.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 157-159
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  • 7
    Publication Date: 2006-03-01
    Description: The stability of equilibrium shapes of elastic systems is examined. Stability loss in the case of similar equilibrium shapes, the disappearance of stable equilibrium shapes, and the disappearance of any forms of equilibrium are discussed. The error made by Euler in analyzing stability loss is pointed out, and Mises' truss is used as an example of stability loss in the case of similar equilibrium shapes.
    Keywords: STRUCTURAL MECHANICS
    Type: Stability and Oscillation of Elastic Systems: Mod. Concepts, Paradoxes and Errors (NASA-TT-F-751); p 1-183
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  • 8
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    In:  CASI
    Publication Date: 2006-03-01
    Description: Problems of oscillations of linear systems are discussed, including systems with a fractional number of degrees of freedom as well as free oscillations of a cantilever in the field of centrifugal forces. Four methods of solving the problem of the action of periodic instantaneous impulses are presented. The Tacoma catastrophe is analyzed and used as an example of aeroelastic oscillations. Problems of nonlinear system oscillations include the vibration maintenance of rotation, the Sommerfeld effect, and self-oscillations of a quasi-system with dry friction.
    Keywords: STRUCTURAL MECHANICS
    Type: Stability and Oscillation of Elastic Systems: Mod. Concepts, Paradoxes and Errors NASA-TT-F-751); p 184-418
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  • 9
    Publication Date: 2006-03-28
    Description: The problem is discussed of identification of a linear object of known structure, the movement of which is described by a system of differential equations of the type y = Ay + Bu, where y is an n-dimensional output vector, u is an m-dimensional vector of stationary, random disturbances (inputs), A and B are matrices of unknown parameters of the dimension, n x n and n x m, respectively. The spectral and reciprocal spectral densities of the inputs and outputs are used as the initial information on the object.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 139-141
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  • 10
    Publication Date: 2006-03-28
    Description: Radial and axial vibration measurements on the scanning disk and the data storage board of an optical-mechanical scanner are evaluated. Statistical processing of the observational data establishes the excitation source and determines the effect of disk torsional vibrations on the data storage board.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 105-106
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  • 11
    Publication Date: 2006-03-28
    Description: The torque of a drive shaft in a magnetic recording device was studied by oscillographic recordings. Statistical evaluation of the dynamic spectral densities showed that the principle source of disturbing forces is loading in the drive shaft radial play.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 103-104
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  • 12
    Publication Date: 2006-03-28
    Description: The equation of motion was used to examine the problem of vibrations of a thin elastic plate covered with a thin viscous layer. Mathematical formulation and the solution of the problem are given.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 89-90
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  • 13
    Publication Date: 2006-03-28
    Description: The statistical characteristics of complex variation amplitudes of shells excited by harmonic force sources in the sound frequency range are examined. Vibrations were measured with a multichannel unit, permitting the component values of a complex vibration amplitude for the i-th measurement point to be obtained at each measured point. An estimation was also made of the nature of the vibration field structure.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 68-73
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  • 14
    Publication Date: 2006-03-28
    Description: A traveling wave unit was built to process measurement data on spatial damping parameters and to simplify statistical treatment of the results. Mean values of the loss coefficient, lengths of flexual waves, and wave propagation velocities for a given set of discrete functions were determined. Results are given in a table.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 81-82
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  • 15
    Publication Date: 2006-03-28
    Description: A method is proposed for determining vibroacoustic characteristics from the results of measurements of the distribution of vibrational energy in a structure. The method is based on an energy model of a structure studied earlier. Equations are written to describe the distribution of vibrational energy in a hypothetical diffuse energy state in structural elements.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 74-77
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  • 16
    Publication Date: 2006-03-28
    Description: The distribution pattern of the amplitudes of vibrations, measured at various points on the surface of a shell, stimulated by a point source of harmonic force in the sound frequency range was studied experimentally. This pattern permits a valid spacing estimate to be carried out of the average structural characteristics of the vibrations, which are used for both estimation of the vibration excitability of the structure and for estimation of the effectiveness of use of a vibration-absorbing covering.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 61-67
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  • 17
    Publication Date: 2006-03-28
    Description: A method, developed for making measurements in reverberation chambers in the steady state mode, is reported. Spatial distribution patterns of the square of the sound pressure vs type of exciting signal were produced theoretically and checked experimentally in a reverberation chamber. Results of measurements of spatial irregularities of the field with pure tones and with noise bands in the 200 to 2,000 Hz frequency range were used for calculating statistical parameters of the reverbation fields by computer. The calculation program included determination of density probability function, integral distribution pattern, mathematical expectation, normalized dispersion of the mean square of the pressure.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 57-60
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  • 18
    Publication Date: 2006-03-28
    Description: Research was begun into the dynamic characteristics of wires, including the self-damping properties. A series of wire insulator fastenings, with and without dampers, was also developed.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 48-49
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  • 19
    Publication Date: 2006-03-28
    Description: Various calculation schemes were proposed for describing vibrations in a piping system with pulsating flow. Methods were selected and applied according to the type of irregularities examined: concentrated ones, extended ones, or complex ones. The selection of a method also depends on comparability of the extent of the irregularities with the pressure wavelength and velocity in the flow. Relations were found which permit a description of the interaction of a pulsating flow with any irregularity in the system. For complex systems with varying temperatures and some irregularities, relations were obtained, which reflect the varying phase displacement of the forces in these irregularities. The effect of the frictional torque on pipeline supports, in the presence of flexural and torsional vibrations was investigated, on the assumption that the frictional torque depends linearly on the angular velocity.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 51-52
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  • 20
    Publication Date: 2006-03-28
    Description: Certain characteristics of the reactions of typical skin panels of a passenger aircraft to acoustical loading are being investigated, for development of an objective method of diagnostics for skin condition, under the operations and maintenance sections of civil aviation. There are a number of difficulties connected with the solution of this problem. The reactions of skin panels exposed to the noises of the exhaust jets are dependent on the aircraft operating conditions, the geometric parameters and limiting conditions of the panels.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 41-43
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  • 21
    Publication Date: 2006-03-28
    Description: A program was compiled for calculating acoustical pressure levels, which might be created by vibrations of complex structures (an assembly of shells and rods), under the influence of a given force, for cases when these fields cannot be measured directly. The acoustical field is determined according to transition frequency and pulse characteristics of the structure in the projection mode. Projection characteristics are equal to the reception characteristics, for vibrating systems in which the reciprocity principle holds true. Characteristics in the receiving mode are calculated on the basis of experimental data on a point pulse space velocity source (input signal) and vibration response of the structure (output signal). The space velocity of a pulse source, set at a point in space r, where it is necessary to calculate the sound field of the structure p(r,t), is determined by measurements of acoustic pressure, created by a point source at a distance R. The vibration response is measured at the point where the forces F and f exciting the system should act.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 53-56
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  • 22
    Publication Date: 2006-03-28
    Description: Endless structures are realized in practice, in the presence of loss and to an adequate extent, owing to which, reflections from the edges to the center part of the structure can be disregarded. In the absence of losses, reflections from the boundary frequently have to be taken into account. In this case, besides compensation for waves passing through the boundary, the reciprocal connection system can be used for compensation of the total field ahead of the boundary. In these cases, the system converters can be located in a different manner relative to the boundary and to one another. Each of the locations has inherent peculiarities, which must be taken into account in solving specific problems.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 222-228
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  • 23
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    In:  CASI
    Publication Date: 2006-03-28
    Description: The vibration characteristics of an unidimensional structure are discussed. The cases considered are: (1) a rigid pipe in which a wave propagates, (2) an infinite string along which a transverse wave propagates, (3) a rod along which longitudinal or torsional columns propagate, and (4) generally a unidimensional propagation of some one mode of vibrations which is nondegenerating with distance. Mathematical models are developed to show the performance of the mechanical devices under various damping conditions.
    Keywords: STRUCTURAL MECHANICS
    Type: Cybernetic Diagnostics of Mech. Systems with Vibro-acoustic Phenomena (NASA-TT-F-14899); p 216-221
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  • 24
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    Publication Date: 2011-08-16
    Description: Description of a variable step incremental procedure for the solution of nonlinear equations in finite element structural analysis. The proposed procedure is effective in improving the accuracy of the basic incremental technique and in providing, in addition, an accurate estimate of the discretization error. The proposed approach is highly appropriate for solving problems for which the user has no a priori estimate of the step size to use.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering; 7; 4, 19; 1973
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  • 25
    Publication Date: 2011-08-16
    Description: Numerical solutions are presented for the problem of minimum weight design of a thin one-dimensional, simply supported, solid panel in compression, with one side exposed to a parallel high supersonic air flow. The flutter speed is held fixed and a minimum thickness constraint is imposed.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering; 7; 4, 19; 1973
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  • 26
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    Publication Date: 2011-08-16
    Description: The philosophy of fracture mechanics is reviewed and utilized to formulate a simplified approach to the determination of the stress-intensity factor photoelastically for three-dimensional problems. The method involves a Taylor Series correction for the maximum in-plane shear stress (TSCM) and does not involve stress separation. The results are illustrated by applying the TSCM to surface flaws in bending fields. Other three-dimensional problems solved by the TSCM are cited.
    Keywords: STRUCTURAL MECHANICS
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  • 27
    Publication Date: 2011-08-16
    Description: Fundamental characterization of the constant-amplitude fatigue crack propagation is achieved by an analysis of the rate of change of crack length with change in number of applied loading cycles, defining the rate values such that they are consistent with the basic assumption of smoothness and continuity in the fatigue crack growth process. The technique used to satisfy the analytical conditions and minimize the effects of local material anomalies and experimental errors is that of fitting a smooth curve to the entire set of basic data by least square regression. This yields a well-behaved function relating the number of cycles to the crack length. By taking the first derivative of the function, the crack growth rate is obtained for each point. The class of curve fitting functions used in the analysis is the polynomial of degree n.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 9; Mar. 197
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  • 28
    Publication Date: 2011-08-16
    Description: This paper gives an overview of the development and status of an improved numerical process for the solution of solid mechanics problems. The proposed process uses a mixed formulation with the fundamental unknowns consisting of both stress and displacement parameters. The problem is formulated either by means of first-order partial differential equations or in a variational form by using a Hellinger-Reissner-type mixed variational principle. For presentation purposes, the components of a numerical process are characterized and the criteria for an ideal process are outlined. Commonly used finite-difference and finite-element procedures are examined in the light of these criteria and it is shown that they fall short in a number of ways. The proposed numerical process, on the other hand, satisfies most of the optimality criteria and appears to be particularly suited for use with the forthcoming generation computers.
    Keywords: STRUCTURAL MECHANICS
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  • 29
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    Publication Date: 2011-08-16
    Description: The purpose of this paper is to develop a sufficiently accurate analysis, which is much simpler than exact three-dimensional analysis, for statics and dynamics of composite laminates. The governing differential equations and boundary conditions are derived by following a variational approach. The displacements are assumed piecewise linear across the thickness and the effects of transverse shear deformations and rotary inertia are included. A procedure for obtaining the general solution of the above governing differential equations in the form of hyperbolic-trigonometric series is given. The accuracy of the present theory is assessed by obtaining results for free vibrations and flexure of simply supported rectangular laminates and comparing them with results from exact three-dimensional analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 30; Oct. 22
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  • 30
    Publication Date: 2011-08-19
    Description: A constitutive theory is presented for representing the anisotropic viscoplastic behavior of high-temperature alloys that possess directional properties resulting from controlled grain growth or solidification. The theory is an extension of a viscoplastic model that has been applied in structural analyses involving isotropic metals. Anisotropy is introduced through the definition of a vector field that identifies a preferential (solidification) direction at each material point. Following the development of a full multiaxial theory, application is made to homogeneously stressed elements in pure shear and to a uniaxially stressed rectangular block in plane stress with the stress direction oriented at an arbitrary angle with the material direction. It is shown that an additional material parameter introduced to characterize the degree of anisotropy can be determined on the basis of simple creep tests.
    Keywords: STRUCTURAL MECHANICS
    Type: Nuclear Engineering and Design (ISSN 0029-5493); 83; 389-396
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  • 31
    Publication Date: 2011-08-18
    Description: The force input mobility of an infinite elastic circular cylindrical shell filled with fluid is derived by using the spectral equations of motion. Mobilities are evaluated and their physical interpretations are discussed for a steel shell of thickness h/a = 0.05 filled with water and vibrating in the n = 0, 1 and 2 circumferential modes. The results are subsequently used to analyze the related situations of wave transmission through a radial ring constraint and the far field vibrational energy distributions between the contained fluid and the shell wall for line and point driving forces.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration (ISSN 0022-460X); 87; 409-427
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  • 32
    Publication Date: 2011-08-18
    Description: The boundary collocation method was used to generate Mode 1 stress intensity and crack mouth opening displacement coefficients for externally radially cracked ring segments subjected to three point radial loading. Numerical results were obtained for ring segment outer-to-inner radius ratios (R sub o/R sub i) ranging from 1.10 to 2.50 and crack length to segment width ratios (a/W) ranging from 0.1 to 0.8. Stress intensity and crack mouth displacement coefficients were found to depend on the ratios R sub o/R sub i and a/W as well as the included angle between the directions of the reaction forces. Previously announced in STAR as N83-35413
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Testing and Evaluation (ISSN 0090-3973); 11; 357-359
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  • 33
    Publication Date: 2011-08-16
    Description: Analytical and experimental data on the vibration characteristics of cantilevered winglike flat trapezoidal aluminum plates are presented. The plates had been reinforced with boron-epoxy composite material which had been placed symmetrically about the plate middle surface. The effect of filament orientation on the mode shapes and frequencies of the first ten modes and on the damping coefficients of several of the lowest frequency modes has been investigated experimentally. Experimental data are compared with results from a finite-element analysis. Stiffness properties of the composite material for use in the analysis were determined from vibration tests of composite reinforced aluminum beams.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Composite Materials; 7; July 197
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  • 34
    Publication Date: 2011-08-16
    Description: The Neuber stress-concentration relation for notches in an elastic-plastic material subjected to shear loading was generalized for a crack in a finite plate subjected to tensile loading. An equation was derived which related the linear elastic stress-intensity factor, the applied stress, and two material parameters. The equation was then used as a two-parameter fracture criterion for surface- and through-cracked specimens. Fracture data from the literature on surface- and through-cracked sheet and plate specimens of steel, titanium alloy, titanium weldment, and aluminum alloy tested at room and cryogenic temperature were analyzed according to the proposed equation. For surface cracks, wide ranges of crack-depth to crack-length ratio and crack-depth to specimen-thickness ratio were considered. For through cracks, wide ranges of crack length and specimen width were also considered.-
    Keywords: STRUCTURAL MECHANICS
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  • 35
    Publication Date: 2011-08-16
    Description: A problem in the linear theory of elasticity is considered wherein a layer with a circular cylindrical hole is subjected to a nonuniform axisymmetric radial displacement. The solution utilizes Navier's equations of elasticity which are solved by means of extended Hankel transforms. A special case in which the radial displacement is a linear function of the axial coordinate is presented. Numerical results are given in graphical form for the case when hole radius and layer thickness are equal. The inversion integrals were evaluated numerically using Longman's technique for computing infinite integrals of oscillatory functions.
    Keywords: STRUCTURAL MECHANICS
    Type: Acta Mechanica; 17; 1-2,; 1973
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  • 36
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    Publication Date: 2011-08-16
    Description: A simple, inexpensive method for studying slow crack growth is described. The method entails measurements of load relaxation at constant displacement using a double torsion specimen. It is demonstrated that the data generated using this technique are in excellent agreement with data obtained using the more complex conventional techniques, for a range of materials - steel, titanium, glass, aluminum oxide, PMMA. These encouraging initial results suggest that additional and more detailed studies using this test procedure are merited.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Testing and Evaluation; 1; July 197
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  • 37
    Publication Date: 2011-08-16
    Description: A general design algorithm based on methods of feasible directions is presented. Zoutendijk's method of feasible directions is first presented as applied to structural design. This method is modified to improve numerical stability of the design process and is then further modified to deal efficiently with infeasible designs. The algorithm requires the analytic gradient of the objective function and the constraint functions which are active at a given stage in the design process. Gradient information is not required for nonactive constraints. Complex constraint functions may be ignored in the initial design stages because violation of these constraints is efficiently overcome later in the design process. The algorithm is demonstrated with elastic design of redundant trusses.
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  • 38
    Publication Date: 2011-08-16
    Description: Analysis of the vibration of the internal structure of a relatively simple flight vehicle structural model consisting of a multicellular box in which two parallel outer face plates (skins) are connected together by several internal plates (ribs) which are parallel to each other and normal to the face plates. Such a box is representative of a wing or stabilizer structure. Three representations of the structure were considered in the computation. The simplest model which can account for the coupling between the face plates and the ribs is a two-dimensional assembly of beams. A more realistic, yet still simple, three-dimensional model has been developed using the Rayleigh-Ritz method. The third computational method employed was the NASTRAN finite-element displacement method. The computational results are compared with experimental data.
    Keywords: STRUCTURAL MECHANICS
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  • 39
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    Publication Date: 2011-08-16
    Description: To prepare for new demands on aircraft structures, NASA has established a number of goals. These include automatic analysis and design, building confidence in advanced composites, improving the technology base for future supersonic and hypersonic vehicles, validating concepts for active controls, developing methods for predicting aircraft loads and aeroelasticity, and generating design methods for assuring structural integrity. Progress made in achieving these goals is discussed in detail.
    Keywords: STRUCTURAL MECHANICS
    Type: Astronautics and Aeronautics; 11; July 197
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  • 40
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    In:  Other Sources
    Publication Date: 2011-08-16
    Description: The effect of the gyroscopic moment on the appearance of a first imaginary critical velocity (minimum negative value of lambda) is investigated and shown to have an important effect on the computation of the first critical velocity. A numerical procedure is developed which can be used for overcoming the difficulties arising when the first real and the first imaginary roots are similar in modulus. As an example, a real shaft with two supports was analyzed. For the computation the real shaft was subdivided into ten sections, and for two of them (representing compressor and turbine) the gyroscopic moment was taken into account. The present method is especially useful when high speed computational facilities are not available.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 11; June 197
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  • 41
    Publication Date: 2011-08-16
    Description: Investigation of the effect of using plane quadrilateral membrane elements for modeling nonplanar structures. The effect is assessed by analyzing a simplified finite element model with the aid of the structure network analysis program. The results obtained indicate that the use of planar quadrilateral membrane elements for modeling bending problems can lead to large errors if the four points that define the quadrilateral are not in the same plane.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 11; May 1973
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  • 42
    Publication Date: 2011-08-16
    Description: A mixed finite-difference scheme is presented for the stress and free vibration analysis of simply supported nonhomogeneous and layered orthotropic thick plates. The analytical formulation is based on the linear, three-dimensional theory of orthotropic elasticity and a Fourier approach is used to reduce the governing equations to six first-order ordinary differential equations in the thickness coordinate. The governing equations possess a symmetric coefficient matrix and are free of derivatives of the elastic characteristics of the plate. In the finite difference discretization two interlacing grids are used for the different fundamental unknowns in such a way as to reduce both the local discretization error and the bandwidth of the resulting finite-difference field equations. Numerical studies are presented for the effects of reducing the interior and boundary discretization errors and of mesh refinement on the accuracy and convergence of solutions. It is shown that the proposed scheme, in addition to a number of other advantages, leads to highly accurate results, even when a small number of finite difference intervals is used.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 3; Sept
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  • 43
    Publication Date: 2011-08-16
    Description: The uses of compliance measurements in linear fracture mechanics are discussed as a technique for determining the crack-extension force vs load, specimen dimensions, and elastic constants. Some practical examples of application are given, including specimen and transducer descriptions, experimental procedure, instrumentation, calculations, measurement precautions, friction effects, and data reduction. The limitations and advantages of compliance measurements are discussed. It is pointed out that good results can be obtained by the compliance method when its measurement precision is not lower than that required for Young's modulus.
    Keywords: STRUCTURAL MECHANICS
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  • 44
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    Publication Date: 2011-08-16
    Description: Summary of some of the results of a recent study of the reliability and range of validity of two-dimensional plate theories in application to low-frequency free vibration analysis of simply supported, bidirectional, multilayered plates consisting of a large number of layers. These results show that for composite plates the error in the predictions of the classical plate theory is strongly dependent on the number and stacking of the layers, in addition to the degree of orthotropy of the individual layers and the thickness ratio of the plate.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 11; July 197
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  • 45
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    Publication Date: 2011-08-16
    Description: Generalized random forces for rectangular panels under subsonic and supersonic boundary-layer turbulence are studied in time domain by a Monte Carlo approach. Panels with simple, fixed, elastic-free, and periodic elastic boundary conditions are considered. The nature of probability structure, peak distribution, threshold crossing, and cross spectral density is investigated.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 11; July 197
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  • 46
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    Publication Date: 2011-08-16
    Description: The paper presents an iterative, finite element method for minimum weight design of structures with respect to buckling constraints. The redesign equation is derived from the optimality criterion, as opposed to a numerical search procedure, and can handle problems that are characterized by the existence of two fundamental buckling modes at the optimal design. Application of the method is illustrated by beam and orthogonal frame design problems.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Solids and Structures; 9; July 197
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  • 47
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    Publication Date: 2011-08-16
    Description: The paper reviews briefly the current design philosophies for achieving long, efficient, and reliable service in aircraft structures. The strengths and weaknesses of these design philosophies and their demonstrated records of success are discussed. The state of the art has not been developed to the point where designing can be done without major test inspection and maintenance programs. A broad program of research is proposed through which a viable computerized design scheme will be provided during the next decade. The program will organize and correlate existing knowledge on fatigue and fracture behavior, identify gaps in this knowledge, and guide specific research to upgrade design capabilities.
    Keywords: STRUCTURAL MECHANICS
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  • 48
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    Publication Date: 2011-08-16
    Description: In this paper a three-dimensional analysis for statics and dynamics of a class of simply supported rectangular plates made up of micropolar elastic material is presented. The solution is in the form of series, in which each term is explicitly determined. For free vibrations, the frequencies are obtained by the solution of a closed form characteristic equation.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Engineering Science; 11; Feb. 197
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  • 49
    Publication Date: 2011-08-16
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Solids and Structures; 9; Jan. 197
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  • 50
    Publication Date: 2011-08-18
    Description: Two methods for identifying the mass, damping and stiffness matrices of a linear vibrating system are presented. Both methods require the measurement of acceleration, velocity and displacement at various locations of the system. In the first method, the response of the system subjected to known forces is used while the second method employs the free vibration data. The unknown parameters are recovered through the standard least squares procedure. Numerical results are presented for several examples.
    Keywords: STRUCTURAL MECHANICS
    Type: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 511-520
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  • 51
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    Publication Date: 2011-08-18
    Description: The problem of potential instability caused by actuator dynamics is examined. Two ways of overcoming it are discussed: rate feedback with compensation and position feedback with tuning filters.
    Keywords: STRUCTURAL MECHANICS
    Type: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 119-142
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  • 52
    Publication Date: 2011-08-18
    Description: (Previously announced in STAR as N82-24501)
    Keywords: STRUCTURAL MECHANICS
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  • 53
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    Publication Date: 2011-08-18
    Description: Problems encountered by aerospace designers in attempting to optimize whole aircraft are discussed, along with possible solutions. Large scale optimization, as opposed to component-by-component optimization, is hindered by computational costs, software inflexibility, concentration on a single, rather than trade-off, design methodology and the incompatibility of large-scale optimization with single program, single computer methods. The software problem can be approached by placing the full analysis outside of the optimization loop. Full analysis is then performed only periodically. Problem-dependent software can be removed from the generic code using a systems programming technique, and then embody the definitions of design variables, objective function and design constraints. Trade-off algorithms can be used at the design points to obtain quantitative answers. Finally, decomposing the large-scale problem into independent subproblems allows systematic optimization of the problems by an organization of people and machines.
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  • 54
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    Publication Date: 2011-08-18
    Description: A simplified buckling analysis is presented for a family of periodic lattice structures such as those proposed for large space structures. A transcendental 6 x 6 matrix of eigenvalues is shown to be sufficient for modeling buckling behavior because member stiffnesses are based on an exact solution of the beam-column equation. Exact stiffnesses are derived for a curved member, thus allowing modeling of imperfect lattice structures. Comparisons of predictions of the lattice model with those available from shell and beam theory underscore the inaccuracies introduced by treating the lattice structure as a continuum. Sample calculations are provided for an isogrid cylinder and a three element double-laced truss.
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  • 55
    Publication Date: 2011-08-18
    Description: Truss beams with members having viscous damping are modeled with a Timoshenko beam. Procedures for deriving the equivalent bending rigidity, transverse shear rigidity, and damping are presented. Explicit expressions for these equivalent beam properties are obtained for a specific truss beam. The beam model thus established is then used to investigate the effect of damping in free vibration. Finally, the beam is employed in the estimation of structural parameters in a simply-supported truss beam using a random search algorithm.
    Keywords: STRUCTURAL MECHANICS
    Type: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 531-545
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  • 56
    Publication Date: 2011-08-18
    Description: A general approach for distributed parameter modeling of complex dynamical systems is described. The method consists of dividing the system in parts which can be modeled by simple partial differential equations and coupling the equations thus obtained by applying Hamilton's variational formalism to the entire system. The modeling of a large, offset-fed, wrap-rib antenna is presented to illustrate the approach. Although such models are perhaps not as precise as finite element models, they can be useful for initial physical insight and parametric design.
    Keywords: STRUCTURAL MECHANICS
    Type: Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 89-102
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  • 57
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    Publication Date: 2011-08-18
    Description: The hybrid experimental-numerical stress-analysis technique, which saw limited applications during the 1950's, has been resurrected with the vastly improved numerical techniques of the 1970's. By inputing the experimental results as initial and boundary conditions, modern computer codes are executed in its generation and application modes to yield results which are unobtainable when only one of the two techniques is used. The hybrid technique thus exemplifies the complementary role of the experimental and numerical techniques.
    Keywords: STRUCTURAL MECHANICS
    Type: (ISSN 0014-4851)
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  • 58
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    Publication Date: 2011-08-18
    Description: Fourier transforms and the Wiener-Hopf technique are used in conjunction with plane elastostatics to examine the singular crack tip stress field in the double cantilever beam (DCB) specimen. In place of the Dirac delta function, a family of functions which duplicates the important features of the concentrated forces without introducing unmanageable mathematical complexities is used as a loading function. With terms of order h-squared/a-squared retained in the series expansion, the dimensionless stress intensity factor is found to be K (h to the 1/2)/P = 12 to the 1/2 (a/h + 0.6728 + 0.0377 h-squared/a-squared), in which P is the magnitude of the concentrated forces per unit thickness, a is the distance from the crack tip to the points of load application, and h is the height of each cantilever beam. The result is similar to that obtained by Gross and Srawley by fitting a line to discrete results from their boundary collocation analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture (ISSN 0376-9429); 22; June 198
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  • 59
    Publication Date: 2011-08-18
    Description: A fracture mechanics approach to the well-known delamination problem in composite materials is presented. Based on the theory of anisotropic laminate elasticity and interlaminar fracture mechanics concepts, the composite delamination problem is formulated and solved. The exact order of the delamination crack-tip stress singularity is determined. Asymptotic stress and displacement fields for an interlaminar crack are obtained. Fracture mechanics parameters such as mixed-mode stress intensity factors, KI, KII, KIII, and the energy release rate, G, for composite delamination problems are defined. To illustrate the fundamental nature of the delamination crack behavior, solutions for edge-delaminated graphite-epoxy composites under uniform axial extension are presented. Effects of fiber orientation, ply thickness, and delamination length on the interlaminar fracture are examined.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Composite Materials (ISSN 0021-9983); 17; May 1983
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  • 60
    Publication Date: 2011-08-18
    Description: Previously cited in issue 13, p. 2112, Accession no. A82-30182
    Keywords: STRUCTURAL MECHANICS
    Type: (ISSN 0001-1452)
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  • 61
    Publication Date: 2011-08-18
    Description: Stress-intensity factors are obtained for point loaded equal length cracks emanating from a circular hole in an infinite plate. A series approach and the Muskhelishvili formulation in the two-dimensional theory of elasticity are used to derive the solution. The applicability of the solution is demonstrated by using it as a Green's function to obtain stress-intensity factors in the case of (1) biaxial tension and pure shear of an infinite plate and (2) tension and pin loading of a plate with cracks emanating from one hole in a row of holes.
    Keywords: STRUCTURAL MECHANICS
    Type: Res Mechanica (ISSN 0143-0084); 9; 2, 19; 1983
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  • 62
    Publication Date: 2011-08-18
    Description: Previously cited in issue 13, p. 2111, Accession no. A82-30171
    Keywords: STRUCTURAL MECHANICS
    Type: (ISSN 0021-8669)
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  • 63
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    Publication Date: 2011-08-18
    Description: Previously cited in issue 13, p. 2110, Accession no. A82-30166
    Keywords: STRUCTURAL MECHANICS
    Type: (ISSN 0001-1452)
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  • 64
    Publication Date: 2016-06-07
    Description: The objectives of the hot section technology (HOST) burner liner cyclic rig test program are basically threefold: (1) to assist in developing predictive tools needed to improve design analyses and procedures for the efficient and accurate prediction of burner liner structural response; (2) to calibrate, evaluate and validate these predictive tools by comparing the predicted results with the experimental data generated in the tests; and (3) to evaluate existing as well as advanced temperature and strain measurement instrumentation, both contact and noncontact, in a simulated engine cycle environment. The data generated will include measurements of the thermal environment (metal surface temperatures) as well as structural (strain) and life (fatigue) responses of simulated burner liners and specimens under controlled boundary and operating conditions. These data will be used to calibrate, compare and validate analytical theories, methodologies and design procedures, as well as improvements in them, for predicting liner temperatures, stress-strain responses and cycles to failure. Comparison of predicted results with experimental data will be used to show where the predictive theories, etc. need improvements. In addition, as the predictive tools, as well as the tests, test methods, and data acquisition and reduction techniques, are developed and validated, a proven, integrated analysis/experiment method will be developed to determine the cyclic life of a simulated burner liner.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Eng. Hot Sect. Technol. (HOST); p 181-193
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  • 65
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    Publication Date: 2016-06-07
    Description: The HOST Liner Cyclic Program is utilizing two types of test apparatus, rectangular box rigs and a full annular rig. To date two quartz lamp cyclic box rigs have been tested and a third is to begin testing in late October 1983. The box rigs are used to evaluate 5x8 inch rectangular linear samples. A 21 inch diameter outer liner simulator is also being built up for testing beginning in April 1984. All rigs are atmospheric rigs. The first box rig, a three 6-kVA lamp installation, was operated under adverse conditions to determine feasibility of using quartz lamps for cyclic testing. This work was done in December 1981 and looked promising. The second box rig, again using three 6-kVA lamps, was operated to obtain instrumentation durability information and initial data input to a Finite Element Model. This limited test program was conducted in August 1983. Five test plates were run. Instrumentation consisted of strain gages, thermocouples and thermal paint. The strain gages were found to fail at 1200 F as expected though plates were heated to 1700 F. The third box rig, containing four 6-kVA lamps, is in build up for testing to begin in late October 1983. In addition to 33 percent greater power input, this rig has provision for 400 F backside line cooling air and a viewing port suitable for IR camera viewing. The casing is also water cooled for extended durability.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Eng. Hot Sect. Technol. (HOST); p 195-204
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  • 66
    Publication Date: 2016-06-07
    Description: The objective of this program is to produce a series of new computer codes that permit more accurate and efficient three dimensional inelastic analysis of selected hot section components - combustor liners, turbine blades and turbine vanes. The computer codes embody a progression of mathematical models and are streamlined to take advantage of geometrical features, loading conditions, and forms of material response that distinguish each group of selected components.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Turbine Eng. Hot Sect. Technol. (HOST); p 179-180
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  • 67
    Publication Date: 2016-06-07
    Description: The objective of this research is to develop an analytical tool capable of economically evaluating the cyclic time dependent plasticity which occurs in hot section engine components in areas of strain concentration resulting from the combination of both mechanical and thermal stresses. The techniques developed must be capable of accommodating large excursions in temperatures with the associated variations in material properties including plasticity and creep. The overall objective of this proposed program is to develop advanced 3-D inelastic structural/stress analysis methods and solution strategies for more accurate and yet more cost effective analysis of combustors, turbine blades, and vanes. The approach will be to develop four different theories, one linear and three higher order with increasing complexities including embedded singularities.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Turbine Eng. Hot Sect. Technol. (HOST); p 175-177
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  • 68
    Publication Date: 2014-09-11
    Description: The dynamic characteristics of the Solar Array Flight Experiment (SAFE) structure during deployment and retraction are investigated. The SAFE structure consists of a deployable mast with an attached solar blanket designed with accordion type folds to permit packaging in a small volume. The planar form of the blanket geometry during deployment is maintained by a blanket tension/guidewire system. Structurally, the mast is modeled as an Euler beam column with inplane and out of plane bending and finite torsional stiffness. For out of plane motion, the blanket is modeled as a distributed mass uniformly supported by the three guidewires. For inplane motion the blanket displacements are assumed to vary linearly from the mast base to the mast tip. The mathematical model uses a virtual work formulation, required because the axial loading on the mast is nonconservative, combined with assumed beam modes to derive the differential equations of motion. Consideration of the time dependent boundary conditions results in an infinite set of ODE with time dependent coefficients. Finally, correlation of mast tip accelerations to mast base bending moments for specified modal motions are indicated.
    Keywords: STRUCTURAL MECHANICS
    Type: Res. Rept.: 1983 NASA(ASEE Summer Faculty Fellowship Program; 24 p
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  • 69
    Publication Date: 2014-09-11
    Description: Traditional composite lamination theory was used to predict composite graphite-epoxy laminate stiffnesses for comparison to quasi-experimental stiffnesses developed from cylindrical bottle pressure testing. Stiffness sensitivities were examined for variations in constituent materials and geometric properties. The material component interactions examined were the fiber longitudinal and transverse Young's modulus, the fiber shear modulus and primary Poisson's ratio, the resin Young's modulus, shear modulus, and Poisson's ratio. The geometric variation of the helical winding angle was also examined. Two computer programs were written to generate the data used to demonstrate the stiffness variations.
    Keywords: STRUCTURAL MECHANICS
    Type: Alabama Univ. Res. Rept.: 1983 NASA(ASEE Summer Faculty Fellowship Program; 34 p
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  • 70
    Publication Date: 2014-09-10
    Description: An experiment to measure the elastic deflection of the DSS 14 concrete pedestal under the weight of the antenna was conducted in February 1983 and is compared to a similiar experiment made in 1968. Comparison of the results confirms the decrease in elastic modulus measured on core samples recently taken from the pedestal.
    Keywords: STRUCTURAL MECHANICS
    Type: The Telecommun. and Data Acquisition Rept.; p 89-91
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  • 71
    Publication Date: 2011-08-16
    Description: A finite-difference method is developed to determine the large amplitude dynamic responses of thin elastic plates subjected to uniform pressure pulse-type loads. Four different sets of boundary conditions are considered. Some specific problems are solved. The results are compared with approximate solutions obtained by Yamaki (1961). The numerical method presented provides an accurate and efficient approximate solution to the problem, and should be useful as a check on other approximate methods. The grid-size and the time-step necessary for obtaining numerical stability depend on the particular problem. For many cases the method converges rapidly and a rather large grid-size and time-step is adequate.
    Keywords: STRUCTURAL MECHANICS
    Type: American Society of Civil Engineers; Journal
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  • 72
    Publication Date: 2012-05-22
    Description: A procedure for automating the sizing of wing-fuselage airframes was developed and implemented in the form of an operational program. The program combines fully stressed design to determine an overall material distribution with mass-strength and mathematical programming methods to design structural details accounting for realistic design constraints. The practicality and efficiency of the procedure is demonstrated for transport aircraft configurations. The methodology is sufficiently general to be applicable to other large and complex structures.
    Keywords: STRUCTURAL MECHANICS
    Type: AGARD Second Symp. on Structural Optimization; 12 p
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  • 73
    Publication Date: 2011-08-18
    Description: An unconditionally stable implicit-explicit method is proposed for the analysis of transient coupled thermal stress waves, and the computer-implementation aspects of the method are discussed. In the method proposed here, the mechanical displacement and temperature are used as independent variables. The resulting coupled finite element matrix equations are symmetric.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 17; 3, 19; 1983
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  • 74
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    Publication Date: 2011-08-18
    Description: Previously cited in issue 13, p. 2112, Accession no. A82-30186
    Keywords: STRUCTURAL MECHANICS
    Type: (ISSN 0001-1452)
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  • 75
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    Publication Date: 2011-08-18
    Description: Previously cited in issue 13, p. 2108, Accession no. A82-30124
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 21; 1729-173
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  • 76
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    Publication Date: 2011-08-18
    Description: Previously cited in issue 01, p. 60, Accession no. A83-10900
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Aircraft (ISSN 0021-8669); 20; 907-912
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  • 77
    Publication Date: 2011-08-18
    Description: Previously cited in issue 13, p. 2109, Accession no. A82-30152
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Aircraft (ISSN 0021-8669); 20; 899-906
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  • 78
    Publication Date: 2011-08-18
    Description: A fracture mechanics analysis has been developed that describes the progress of delamination damage in composite plates struck by a hard spherical object. The analysis is based on large deflection plate mechanics for circular isotropic plates wherein multiple axisymmetric delaminations grow. Test data show that the analysis predicts the influence of plate thickness, support conditions, and matrix toughness on the onset and propagation of delamination.
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  • 79
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    Publication Date: 2011-08-18
    Description: A three-dimensional element based on the total Lagrangian description of large deformations of a layered anisotropic composite medium is developed, validated, and used to analyze layered composite shells. The element contains the following features: geometric nonlinearity, dynamic (transient) behavior, and arbitrary lamination scheme and lamina properties. Numerical results of nonlinear bending, natural vibration, and transient response are presented to illustrate the capabilities of the element.
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  • 80
    Publication Date: 2016-06-07
    Description: A square plate with clamped edges under a concentrated load was modeled using NASTRAN and ASKA finite element computer programs. Deflections were computed for various width-to-thickness ratios (b/t) of the plate element, and were compared against the classical theory to determine the b/t limitations. A cylinder with simply supported ends was modeled using NASTRAN and STAGS computer programs for buckling analysis. The models were subjected to a uniform radial pressure loading. Several parameters were changed, and the effects of those variations are presented. Utilizing these data, a model which will produce results comparable to published empirical data can be constructed and processed for a minimized cost.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 69-88
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  • 81
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    Publication Date: 2016-06-07
    Description: The objectives of the NASTRAN computer program system are discussed. Specific reference is made to the use of NASTRAN in the space shuttle program. The use of NASTRAN by agencies other than NASA is reported. The subjects presented are: (1) planned developments, (2) capability improvements, (3) efficiency improvements, and (4) new error correction procedure.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: Users' Experiences; p 1-6
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  • 82
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    Publication Date: 2016-06-07
    Description: Primary structures for nuclear power plants are designed to resist expected earthquakes of the site. Two intensities are referred to as Operating Basis Earthquake and Design Basis Earthquake. These structures are required to accommodate these seismic loadings without loss of their functional integrity. Thus, no plastic yield is allowed. The application of NASTRAN in analyzing some of these seismic induced structural dynamic problems is described. NASTRAN, with some modifications, can be used to analyze most structures that are subjected to seismic loads. A brief review of the formulation of seismic-induced structural dynamics is also presented. Two typical structural problems were selected to illustrate the application of the various methods of seismic structural analysis by the NASTRAN system.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 243-249
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  • 83
    Publication Date: 2016-06-07
    Description: The use of the NASTRAN conical shell element in static, eigenvalue, and direct transient analyses is demonstrated. The results of a NASTRAN static solution of an externally pressurized ring-stiffened cylinder agree well with a theoretical discontinuity analysis. Good agreement is also obtained between the NASTRAN direct transient response of a uniform cylinder to a dynamic end load and one-dimensional solutions obtained using a method of characteristics stress wave code and a standing wave solution. Finally, a NASTRAN eigenvalue analysis is performed on a hydroballistic model idealized with conical shell elements.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 125-142
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  • 84
    Publication Date: 2016-06-07
    Description: The application of NASTRAN to a complex piping design evaluation problem is summarized. Emphasis is placed on structural modeling aspects, problems encountered in modeling and analyzing curved pipe sections, principal results, and relative merits of using NASTRAN as a pipe analysis and design tool. In addition, the piping and manifolding system was analyzed with SNAP (Structural Network Analysis Program). The parallel SNAP study provides a basis for limited comparisons between NASTRAN and SNAP as to solution agreement and computer execution time and costs.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: Users' Experiences; p 89-102
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  • 85
    Publication Date: 2016-06-07
    Description: NASTRAN was used to study problems associated with the installation of a linear induction motor reaction rail test track. Specific problems studied include determination of the critical axial compressive buckling stress and establishment of the lateral stiffness of the reaction rail under combined loads. NASTRAN results were compared with experimentally obtained values and satisfactory agreement was obtained. The reaction rail was found to buckle at an axial compressive stress of 11,400 pounds per square inch. The results of this investigation were used to select procedures for installation of the reaction rail.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: Users' Experiences; p 29-48
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  • 86
    Publication Date: 2016-06-07
    Description: The recent introduction of special crack-tip singularity elements, usually referred to as cracked elements, has brought the power and flexibility of the finite-element method to bear much more effectively on fracture mechanics problems. This paper recalls the development of two cracked elements and presents the results of some applications proving their accuracy and economy. Judging from the available literature on numerical methods in fracture mechanics, it seems clear that the elements described have been used more extensively than any others in practical fracture mechanics applications.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 531-550
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  • 87
    Publication Date: 2016-06-07
    Description: Linear, quadratic, and cubic isoparametric hexahedral solid elements have been added to the element library of NASTRAN. These elements are available for static, dynamic, buckling, and heat-transfer analyses. Because the isoparametric element matrices are generated by direct numerical integration over the volume of the element, variations in material properties, temperatures, and stresses within the elements are represented in the computations. In order to compare the accuracy of the new elements, three similar models of a slender cantilever were developed, one for each element. All elements performed well. As expected, however, the linear element model yielded excellent results only when shear behavior predominated. In contrast, the results obtained from the quadratic and cubic element models were excellent in both shear and bending.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 423-437
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  • 88
    Publication Date: 2016-06-07
    Description: A group of 5 lashed identical stream turbine blades is studied through the use of single level substructuring using NASTRAN level 15.1. An altered version, similar to DMAP Program Number 3 of the NASTRAN Newsletter, of Rigid Format 13.0 was used. Steady-state displacements and stresses due to centrifugal loads are obtained both without and with consideration of differential stiffness. The normal mode calculations were performed for blades at rest and at operating speed. Substructuring lowered the computation costs of the analysis by a factor of four.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 301-321
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  • 89
    Publication Date: 2016-06-07
    Description: A numerical analysis is presented for the problem of a flat rectangular rubber membrane with a circular rigid inclusion undergoing high strains due to the action of an axial load. The neo-hookean constitutive equations are introduced into the general purpose TITUS program by means of equivalent hookean constants and initial strains. The convergence is achieved after a few iterations. The method is not limited to any specific program. The results are in good agreement with those of a company sponsored photoelastic stress analysis. The theoretical and experimental deformed shapes also agree very closely with one another. For high strains it is demonstrated that using the conventional HOOKE law the stress concentration factor obtained is unreliable in the case of rubberlike material.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 49-68
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  • 90
    Publication Date: 2016-06-07
    Description: This paper reviews the development of NASTRAN relative to the efficiency of execution, with particular emphasis on those items which have changed significantly since the original release of NASTRAN. Features discussed include main and secondary storage utilization, matrix packing, matrix assembly, matrix multiplication, matrix decomposition and equation solution. Also a brief look into the future discusses the questions of faster arithmetic units and more effective storage utilization. In some cases the improvements in NASTRAN efficiency have resulted from taking advantage of hardware developments, while in other cases increased efficiency has resulted from improvements in the state of the art for data processing or matrix operations. The modular design of NASTRAN has made it possible to improve the efficiency in many parts of NASTRAN without changing the basic design of the program.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 7-28
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  • 91
    facet.materialart.
    Unknown
    In:  CASI
    Publication Date: 2016-06-07
    Description: One of the primary drivers that prompted the initiation of the hot section technology (HOST) program was the recognized need for improved cyclic durability of costly hot section components. All too frequently, fatigue in one form or another was directly responsible for the less than desired durability, and prospects for the future weren't going to improve unless a significant effort was mounted to increase our knowledge and understanding of the elements governing cyclic crack initiation and propagation lifetime. Certainly one of the important factors is the ability to perform accurate structural stress-strain analyses on a routine basis to determine the magnitudes of the localized stresses and strains since it is these localized conditions that govern the initiation and crack growth processes. Developing the ability to more accurately predict crack initiation lifetimes and cyclic crack growth rates for the complex loading conditions found in turbine engine hot sections is of course the ultimate goal of the life prediction research efforts. It has been found convenient to divide the research efforts into those dealing with nominally isotropic and anisotropic alloys; the latter for application to directionally solidified and single crystal turbine blades.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Eng. Hot Sect. Technol. (HOST); p 205-207
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  • 92
    Publication Date: 2016-06-07
    Description: The Hot Section Technology (HOST) Project is a NASA-sponsored endeavor to improve the durability of advanced gas turbine engines for commercial and military aircraft. Through improvements in the analytical models and life prediction systems, designs for future hot section components , the combustor and turbine, will be more accurately analyzed and will incorporate features required for longer life in the more hostile operating environment of high performance engines.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Eng. Hot Sect. Technol. (HOST); p 1-6
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  • 93
    Publication Date: 2016-06-07
    Description: Linear (8 node), parabolic (20 node), cubic (32 node) and mixed (some edges linear, some parabolic and some cubic) have been inserted into NASTRAN, level 15.1. First the dummy element feature was used to check out the stiffness matrix generation routines for the linear element in NASTRAN. Then, the necessary modules of NASTRAN were modified to include the new family of elements. The matrix assembly was changed so that the stiffness matrix of each isoparametric element is only generated once as the time to generate these higher order elements tends to be much longer than the other elements in NASTRAN. This paper presents some of the experiences and difficulties of inserting a new element or family of elements into NASTRAN.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 439-454
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  • 94
    Publication Date: 2016-06-07
    Description: A basic automated substructure analysis capability for NASTRAN is presented which eliminates most of the logistical data handling and generation chores that are currently associated with the method. Rigid formats are proposed which will accomplish this using three new modules, all of which can be added to level 16 with a relatively small effort.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 323-393
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  • 95
    facet.materialart.
    Unknown
    In:  CASI
    Publication Date: 2016-06-07
    Description: The complexities of turbine engine blade vibration are compounded by blade geometry, temperature gradients, and rotational speeds. Experience indicates that dynamics analysis using the finite element approach provides an effective means for predicting vibration characteristics of compressor and turbine blades whose geometry may be irregular, have curved boundaries, and be subjected to high temperatures and speeds. The NASTRAN program was chosen to help analyze the dynamics of normal modes, rotational stiffening and thermal effects on the normal modes, and forced responses. The program has produced reasonable success. This paper presents the analytical procedures and the NASTRAN results, in comparison with a conventional beam element program and laboratory data.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 251-267
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  • 96
    Publication Date: 2016-06-07
    Description: The characteristics of an interactive graphics systems to facilitate the finite element method of structural analysis are described. The finite element model analysis consists of three phases: (1) preprocessing (model generation), (2) problem solution, and (3) postprocessing (interpretation of results). The advantages of interactive graphics to finite element structural analysis are defined.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 679-695
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  • 97
    Publication Date: 2016-06-07
    Description: The design and development of automobile shipping containers to reduce enroute damage are discussed. Vibration tests were conducted to determine the system structural integrity. A dynamic analysis was made using NASTRAN and the results of the test and the analysis are compared.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: Users' Experiences; p 621-625
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  • 98
    Publication Date: 2016-06-07
    Description: Information about principal axes and moments of inertia is presented in terms of formulas involving solely quantities which can be expressed in literal form whenever central principal axes can be located by inspection for at least one state of a deformable system composed of particles and rigid bodies. Two illustrative examples are worked out in detail.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center The 8th Aerospace Mech. Symp.; p 37-48
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  • 99
    facet.materialart.
    Unknown
    In:  CASI
    Publication Date: 2016-06-07
    Description: A new higher order triangular plate-bending finite element is presented which possesses high accuracy for practical mesh subdivisions and which uses only translations and rotations as grid point degrees of freedom. The element has 18 degrees of freedom, the transverse displacement and two rotations at the vertices and mid-side grid points of the triangle. The transverse displacement within the element is approximated by a quintic polynomial; the bending strains thus vary cubically within the element. Transverse shear flexibility is taken into account in the stiffness formulation. Two examples of static and dynamic analysis are included to show the behavior of the element.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: Users' Experiences; p 455-484
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  • 100
    Publication Date: 2016-06-07
    Description: The NASTRAN experiences of a major structural design and fabrication subcontractor that has less engineering personnel and computer facilities than those available to large prime contractors are discussed. Efforts to obtain sufficient computer capacity and the development and implementation of auxiliary programs to reduce manpower requirements are described. Applications of the NASTRAN program for training users, checking out auxiliary programs, performing in-house research and development, and structurally analyzing an Avco designed and manufactured missile case are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 595-609
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