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  • Other Sources  (1,043)
  • STRUCTURAL MECHANICS  (1,043)
  • 1975-1979  (1,043)
  • 1
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    Rapid interface flaw extension with friction (1976)
    In:  CASI
    Details
    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
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    Tests of beaded and tubular structural panels (1978)
    In:  CASI
    Details
    Publication Date: 2006-06-12
    Description: Two efficient concepts built from curved elements were identified, and a data base for tubular panels was developed. The tubular panel failure modes were understood, and the data base for these panels indicated that their performance can be predicted. The concepts are currently being tested in a realistic builtup structure; 157 room temperature tests and 67 hot tests were made with no structural failures, although all of these tests were not at the design load of the structure.
    Keywords: STRUCTURAL MECHANICS
    Type: Recent Advan. in Structures for Hypersonic Flight, Pt. 2; p 538-576
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  • 3
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    Recent advances in thermal-structural analysis and design (1978)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: A continuing effort to develop a comprehensive capability for thermal-structural analysis and automated design (sizing) is reviewed. A principal role in the activity is played by the finite element program SPAR which contains both an efficient structural and thermal analysis capability. The benefit of having thermal and structural analyses in the same finite element program is illustrated by the application of SPAR to design calculations for the National Transonic Facility - a cryogenic wind tunnel under construction at Langley. Some experience with large-scale thermal structural analysis problems, particularly the space shuttle orbiter, has led to the identification of some analysis needs. Those needs include automated model generation and data output for lumped parameter thermal analysis, faster solution methods for nonlinear transient heat transfer, automated interpolation of temperature data from a thermal finite element model to a dissimilar structural finite model, and automated techniques to identify the times at which the critical combinations of transient heating and loads occur on a structure.
    Keywords: STRUCTURAL MECHANICS
    Type: Recent Advan. in Structures for Hypersonic Flight, Pt.2; p 897-941
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  • 4
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    Recent advances in thermostructural finite element analysis (1978)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: A comparison study is described which has indicated that the finite element and lumped parameter methods are comparable for steady-state conduction/convection analyses. The finite element model was advantageous because of the ease of model verification with computer graphics. Some problems encountered in constructing compatible thermal and structural models have indicated the need for further methodology developments to automate the transition between thermal and structural analyses. The need for more efficient finite element nonlinear transient algorithms has been cited. With further development in the thermal analysis area, the finite element method offers high potential for an integrated thermal/structural analysis capability.
    Keywords: STRUCTURAL MECHANICS
    Type: Recent Advan. in Structures for Hypersonic Flight, Pt. 2; p 851-896
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  • 5
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    External insulator for liquid hydrogen tanks (1978)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: With optimized insulation thickness, tank temperatures were always below 311 K (100 F). This conclusion indicated that an aluminum tank could be used with an optimized insulation system if desired. The N2 purged systems were always lighter than CO2 purged systems. The lower condensation temperature was the controlling factor. Closed cell foam systems were lightest. Closed cell foams, in spite of their need for protective outer insulation, produced insulation systems which were lighter than systems which allowed cryodeposition. Foam system durability established for TMAX = 316 K (110 F). Tests for a subsonic application established this durability; higher temperature limit foam durability was unknown at this. An increase in foam TMAX from 316 K (110 F) to 450 K (350 F) potentially decreased TPS mass by 25 percent.
    Keywords: STRUCTURAL MECHANICS
    Type: Recent Advan. in Structures for Hypersonic Flight, Pt. 2; p 807-847
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  • 6
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    Dryden Flight Research Center hot structures research (1978)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: The facilities, testing techniques, and design methods are described for NASA Dryden Flight Research Center. High temperature strain gage technology, realistic flight hardware fabrication, and structural analysis are discussed. A considerable amount of experimental work on hot structure concepts for hypersonic vehicles was performed; all the work is not complete, and there are still problem areas that need to be resolved.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Recent Advan. in Structures for Hypersonic Flight, Pt. 2; p 707-750
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  • 7
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    Multiwall TPS (1978)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: A study of multiwall TPS as an alternative to LRSI for the space shuttle indicated that vented multiwall, with foil thicknesses limited to those used in multiwall fabricated to date, is some what heavier than LRSI. With reduced foil thicknesses, multiwall TPS may equal the weight of LRSI. Metallic conduction through multiwall TPS transfered less heat than gas conduction or radiation. Radiation heat transfer was greatest at high temperatures; however, the number of layers selected can significantly reduce radiation. At low-to-intermediate temperatures, gas conduction transfered the most heat through multiwall TPS. Gas conduction may be eliminated by evacuation of panels. Oxidation rates required a trade of foil thickness against life.
    Keywords: STRUCTURAL MECHANICS
    Type: Recent Advan. in Structures for Hypersonic Flight, Pt. 2; p 671-706
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  • 8
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    Structures and TPS for the NHFRF/HYTID (1978)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: The goal of HYTID was to provide a cost effective hypersonic vehicle constructed of near-state-of art systems and structure with sufficient margins to assure no vehicle flight development problems, and to permit concentration of flight operations on hypersonic research with a broad series of experiments carried in a dedicated payload bay or on the exposed surface of the lower aft fuselage.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Recent Advan. in Structures for Hypersonic Flight, Pt. 2; p 601-627
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  • 9
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    Design and fabrication of a super alloy thermal protection system (1978)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: A lightweight metallic TPS was designed, and two test articles were fabricated, one from Haynes 188 and one from Rene 41. A baseline TPS concept, selected at the beginning of the program, consisted of a Haynes 25 corrugation-stiffened beaded skin surface panel, a specially designed support system, and an insulation system. By optimizing the structure for the design loads and by chem-milling to remove material not needed, the mass of the baseline surface panel was reduced 25%, and the mass of the support structure was reduced 50%. The insulation system mass was reduced 40% by using two types of insulation, each suited to its temperature range, and by eliminating a foul bag which encapsulated the baseline insulation system. These reductions resulted in an overall 35% reduction in mass of the Haynes 188 panel from the baseline Haynes 25 design. Similar reductions were achieved with the Rene 41 system.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Recent Advan. in Structures for Hypersonic Flight, Pt. 2; p 629-669
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  • 10
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    Structures for hypersonic airbreathing tactical missiles (1978)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: The studies to date were encouraging and indicated that materials were available or could be developed to satisfy scramjet requirements. Some of the more promising materials for the critical components were indicated. This information is summarized as follows : (1) radome - Slip cast fused silica is the current candidate, but others are being investigated. One shortcoming of slip cast fused silica is its susceptability to rain damage. (2) inlet leading edges - A refractory metal with a good oxidation protective coating will be required. Tantalum T222 with a Hafnia coating looks promising. (3) inlet ducts - An uninsulated refractory alloy will be required. Columbium F-85 was the best of those considered for the noncircular ducts. (4) external body - The external body temperatures are sufficiently low to permit the use of super alloys. (5) combustor and nozzle - The pyrolytic graphite/silicon carbide coating is very attractive for use in the combustor and nozzle areas.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Recent Advan. in Structures for Hypersonic Flight, Pt. 2; p 577-599
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  • 11
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    Influence of a circular hole under uniform normal pressure on the stresses around a line crack in an infinite plate (1976)
    In:  CASI
    Details
    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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  • 12
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    Combined vibration/temperature/sideload environmental testing of UHF blade antennas (1979)
    In:  CASI
    Details
    Publication Date: 2006-07-02
    Description: Service problems encountered on the F-4 aircraft showed that the environmental qualification requirements for the UHF blade antenna were not adequate. Although the individual environmental levels were stringent enough, only combined environmental testing could duplicate the conditions in which service problems occurred. Techniques for applying static side load simultaneously with vibration and temperature were developed. The combined environment testing was instrumental in the rapid assessment of antenna modifications and resulted in a final configuration which proved satisfactory in service. A need to include combined environmental testing for qualification of blade antennas was established.
    Keywords: STRUCTURAL MECHANICS
    Type: Shock and Vibration Inform. Center The Shock and Vibration Bull., Pt. 3; p 79-84
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  • 13
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    NASTRAN analysis of a wheel-rail loading on its foundation (1978)
    In:  CASI
    Details
    Publication Date: 2006-01-16
    Description: One type of azimuth bearing for a large ground antenna (100 m) will consist of steel wheels, mounted at four corners of the alidade, rolling on a circular flat rail which provides the vertical restraints; a radial constraining bearing at the center of the alidade provides the horizontal restraints. One important design feature is the compressive stresses in the grout or concrete foundation under the wheel-rail load. A finite element analysis check was made of a particular design that consists of a steel rail resting on a concrete foundation. Symmetry was assumed as much as possible in order to minimize the models, but meaningful element sizes were used. Recently developed isoparametric hexahedron elements available in the NASTRAN computing program, which minimizes the number of elements required while maintaining the accuracy of the computed stresses, were used with two versions of NASTRAN. Test cases to check with the analytical solutions were made. A side loading was also applied to calculate the increase in the concrete stresses.
    Keywords: STRUCTURAL MECHANICS
    Type: The Deep Space Network; p 204-215
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  • 14
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    A simplified method of evaluating the stress wave environment of internal equipment (1979)
    In:  CASI
    Details
    Publication Date: 2006-01-16
    Description: A simplified method called the transfer function technique (TFT) was devised for evaluating the stress wave environment in a structure containing internal equipment. The TFT consists of following the initial in-plane stress wave that propagates through a structure subjected to a dynamic load and characterizing how the wave is altered as it is transmitted through intersections of structural members. As a basis for evaluating the TFT, impact experiments and detailed stress wave analyses were performed for structures with two or three, or more members. Transfer functions that relate the wave transmitted through an intersection to the incident wave were deduced from the predicted wave response. By sequentially applying these transfer functions to a structure with several intersections, it was found that the environment produced by the initial stress wave propagating through the structure can be approximated well. The TFT can be used as a design tool or as an analytical tool to determine whether a more detailed wave analysis is warranted.
    Keywords: STRUCTURAL MECHANICS
    Type: Shock and Vibration Inform. Center The Shock and Vibration Bull., Pt. 1; p 89-96
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  • 15
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    High G pyrotechnic shock simulation using metal-to-metal impact (1979)
    In:  CASI
    Details
    Publication Date: 2006-01-16
    Description: A technique for simulating high g level pyrotechnic shocks is described and the results of applying the technique to obtain the MIL-STD-1540A shock spectrum with a maximum acceleration of 18,000g at 2,000 Hz are presented. Designing the resonant beam and plate on which the test unit is mounted, and generating a proper impulsive load on them, were the essentials of the technique. One dimensional stress wave and Euler equations were employed in the design. A metal pendulum hammer was used to generate the impulsive load.
    Keywords: STRUCTURAL MECHANICS
    Type: Shock and Vibration Inform. Center The Shock and Vibration Bull., Pt. 1; p 97-100
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  • 16
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    Probability of failure prediction for step-stress fatigue under sine or random stress (1979)
    In:  CASI
    Details
    Publication Date: 2006-01-16
    Description: A previously proposed cumulative fatigue damage law is extended to predict the probability of failure or fatigue life for structural materials with S-N fatigue curves represented as a scatterband of failure points. The proposed law applies to structures subjected to sinusoidal or random stresses and includes the effect of initial crack (i.e., flaw) sizes. The corrected cycle ratio damage function is shown to have physical significance.
    Keywords: STRUCTURAL MECHANICS
    Type: Shock and Vibration Inform. Center The Shock and Vibration Bull., Pt. 1; p 31-41
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  • 17
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    A study of the effect of subcritical crack growth on the geometry dependence on nonlinear fracture toughness parameters (1976)
    In:  CASI
    Details
    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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  • 18
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    Influence of specimen boundary on the dynamic stress intensity factor (1976)
    In:  CASI
    Details
    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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  • 19
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    Fracture testing with surface crack specimens (1975)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Description: This paper is a report of ASTM Task Group E24.01.05 on Part-Through Crack Testing. It includes recommendations for the design, preparation, and static fracture testing of surface crack specimens based on the current state of the art. The recommendations are preceded by background information including discussions of stress intensity factors, crack opening displacements, and fracture toughness values associated with surface crack specimens. Cyclic-load and sustained-load tests are discussed briefly. Recommendations for further research are included.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Testing and Evaluation; 3; Sept
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  • 20
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    Structural reanalysis via a mixed method (1975)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Description: A study is made of the approximate structural reanalysis technique based on the use of Taylor series expansion of response variables in terms of design variables in conjunction with the mixed method. In addition, comparisons are made with two reanalysis techniques based on the displacement method. These techniques are the Taylor series expansion and the modified reduced basis. It is shown that the use of the reciprocals of the sizing variables as design variables (which is the natural choice in the mixed method) can result in a substantial improvement in the accuracy of the reanalysis technique. Numerical results are presented for a space truss structure.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 5; Apr. 197
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  • 21
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    An orthotropic sandwich plate containing a part-through crack under mixed mode deformation (1978)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Keywords: STRUCTURAL MECHANICS
    Type: Engineering Fracture Mechanics; 10; 1, 19; 1978
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  • 22
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    Finite element solution for beams using an element averaging technique (1978)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: The article investigates the error in the computation of natural frequency through finite element models of the structures when elements of unequal length are chosen and then goes on to suggest an averaging technique for unequal length elements, with different structural properties. Using the element averaging technique, a typical structure has been analysed for its natural frequencies and the results are described.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 8; Feb. 197
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  • 23
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    Displacement coefficients along the inner boundaries of radially cracked ring segments subject to forces and couples (1978)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Displacement results of plane boundary collocation analysis are given for various locations on the inner boundaries of radially cracked ring segments (C-shaped specimens) subject to two complementary types of loading. Results are presented for ratios of outer to inner radius in the range of 1.1 to 2.5 and ratios a/W in the range 0.1 to 0.8, where a is the crack length for a specimen of wall thickness W. By combination of these results the resultant displacement coefficient or the corresponding influence coefficient can be obtained for any practical load line location of a pin-loaded specimen.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Testing and Evaluation; 6; May 1978
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  • 24
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    A new method for predicting response in complex linear systems. II (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: The paper describes convergence and response studies in the low frequency range of complex systems, particularly with low values of damping of different distributions, and reports on the modification of the relaxation procedure required under these conditions. A new method is presented for response estimation in complex lumped parameter linear systems under random or deterministic steady state excitation. The essence of the method is the use of relaxation procedures with a suitable error function to find the estimated response; natural frequencies and normal modes are not computed. For a 45 degree of freedom system, and two relaxation procedures, convergence studies and frequency response estimates were performed. The low frequency studies are considered in the framework of earlier studies (Kayser and Bogdanoff, 1975) involving the mid to high frequency range.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 53; Aug. 22
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  • 25
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    Wave propagation in laminated orthotropic circular cylindrical shells (1976)
    In:  Other Sources
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    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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  • 26
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    Plane-stress fracture of compact and notch-bend specimens (1976)
    In:  Other Sources
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    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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  • 27
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    The shear-stress intensity factor for a centrally cracked stiff-flanged shear web (1976)
    In:  Other Sources
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    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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  • 28
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    Three-dimensional elastic stress and displacement analysis of finite geometry solids containing cracks (1975)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Description: The line method of analysis is applied to the Navier-Cauchy equations of elastic equilibrium to calculate the displacement distributions in various bodies containing cracks. The application of this method to these equations leads to coupled sets of simultaneous ordinary differential equations whose solutions are obtained along sets of lines in a discretized region. When decoupling the equations and their boundary conditions is not possible, the use of a successive approximation procedure permits the analytical solution of the resulting ordinary differential equations. The results obtained show a considerable potential for using this method in the three-dimensional analysis of finite geometry solids and suggest a possible extension of this technique to nonlinear material behavior.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 11; June 197
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  • 29
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    Structural design and analysis. Part 1 (1975)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Description: Topics in anisotropic elasticity are discussed along with the analysis of truss, beam, frame, and membrane components. Attention is given to failure criteria and failure analysis of composite structural components. Other subjects considered are related to the analysis of plates, the analysis of shells, and questions of wave propagation and impact in composite materials. Individual items are announced in this issue.
    Keywords: STRUCTURAL MECHANICS
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  • 30
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    Analysis of truss, beam, frame, and membrane components (1975)
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    Publication Date: 2011-08-16
    Description: Truss components are considered, taking into account composite truss structures, truss analysis, column members, and truss joints. Beam components are discussed, giving attention to composite beams, laminated beams, and sandwich beams. Composite frame components and composite membrane components are examined. A description is given of examples of flat membrane components and examples of curved membrane elements. It is pointed out that composite structural design and analysis is a highly interactive, iterative procedure which does not lend itself readily to characterization by design or analysis function only.-
    Keywords: STRUCTURAL MECHANICS
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  • 31
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    Panel flutter optimization by gradient projection (1975)
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    Publication Date: 2011-08-16
    Description: A gradient projection optimal control algorithm incorporating conjugate gradient directions of search is described and applied to several minimum weight panel design problems subject to a flutter speed constraint. New numerical solutions are obtained for both simply-supported and clamped homogeneous panels of infinite span for various levels of inplane loading and minimum thickness. The minimum thickness inequality constraint is enforced by a simple transformation of variables.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering; 9; 2, 19; 1975
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  • 32
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    Application of boundary integral method to elastoplastic analysis of V-notched beams (1975)
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    Publication Date: 2011-08-16
    Description: The boundary integral equation method was applied in the solution of the plane elastoplastic problems. The use of this method was illustrated by obtaining stress and strain distributions for a number of specimens with a single edge notch and subjected to pure bending. The boundary integral equation method reduced the nonhomogeneous biharmonic equation to two coupled Fredholm-type integral equations. These integral equations were replaced by a system of simultaneous algebraic equations and solved numerically in conjunction with the method of successive elastic solutions.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 11; Apr. 197
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    Mechanics of fracture - Fundamentals and some recent developments (1979)
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    Publication Date: 2011-08-18
    Description: An overview is presented of the fundamental aspects of and recent developments in fracture mechanics. Reference is made to linear elastic fracture mechanics including the state of stresses and displacements in the vicinity of cracks, effects of crack geometry and orientation on stress intensity factors, energy balance of Griffith, Irwin's stress intensity concept, and linear elastic fracture mechanics testing for fracture toughness. Other aspects of this paper include the non-linear behavior of materials and their influence on fracture mechanics parameters, consideration of viscoelasticity and plasticity, non-linear fracture toughness parameters as C.O.D., R-curve and J-integral, and a non-linear energy method, proposed by Liebowitz. Finite element methods applied to fracture mechanics problems are indicated. Also, consideration has been given to slow crack growth, dynamic effects on K(IC), Sih's criterion for fracture, Lee and Liebowitz's criterion relating crack growth with plastic energy, and applications of fracture mechanics to aircraft design. Suggestions are offered for future research efforts to be undertaken in fracture mechanics.
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    NASA-Langley Research Center's participation in a round-robin comparison between some current crack-propagation prediction methods (1979)
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    Publication Date: 2011-08-18
    Description: A round-robin study was conducted which evaluated and compared different methods currently in practice for predicting crack growth in surface-cracked specimens. This report describes the prediction methods used by the Fracture Mechanics Engineering Section, at NASA-Langley Research Center, and presents a comparison between predicted crack growth and crack growth observed in laboratory experiments. For tests at higher stress levels, the correlation between predicted and experimentally determined crack growth was generally quite good. For tests at lower stress levels, the predicted number of cycles to reach a given crack length was consistently higher than the experimentally determined number of cycles. This consistent overestimation of the number of cycles could have resulted from a lack of definition of crack-growth data at low values of the stress intensity range. Generally, the predicted critical flaw sizes were smaller than the experimentally determined critical flaw sizes. This underestimation probably resulted from using plane-strain fracture toughness values to predict failure rather than the more appropriate values based on maximum load.
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    A review and assessment of the stress-intensity factors for surface cracks (1979)
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    Publication Date: 2011-08-18
    Description: The stress-intensity factor solutions proposed for a surface crack in a finite plate subjected to uniform tension are reviewed. Fourteen different solutions obtained over the past 16 years using approximate analytical methods, experimental methods, and engineering estimates are compared. The accuracy of the various solutions is assessed by correlating fracture data on surface-cracked tension specimens made of a brittle epoxy material. Fracture of the epoxy material was characterized by a constant value of stress-intensity factor as failure. Thus, the correctness of various solutions is judged by the variations in the stress-intensity factors at failure. The solutions were ranked in order of minimum standard deviation. The highest ranking solutions correlated 95% of data analyzed within + or - 10% whereas the lowest ranking solutions correlated 95% of data analyzed within + or - 20%. Some solutions could be applied to all data considered, whereas others were limited with respect to crack shapes and crack sizes that could be analyzed.
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    Response of a beam on an inertial foundation to a traveling load (1977)
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    Publication Date: 2011-08-17
    Description: The response of a Bernoulli-Euler beam supported by a Winkler-type elastic foundation with inertia and subjected to a moving load is investigated. Steady-state solutions are determined for an undamped and linearly damped beam-foundation system. The effects on the response of load velocity, foundation mass, and damping are studied. For the undamped system, it is well known that the response grows without bound as a certain critical velocity is approached. It is shown that the effect of foundation mass is to reduce the critical velocity and to increase the peak deflection. The increase in peak deflection becomes more pronounced as the critical velocity is approached. As in the case of massless foundation, the deflection wave is observed to be symmetric with respect to the load. When damping is introduced, the deflection wave loses its symmetry, and the peak deflection is reduced. Results for both cases are given in graphical form.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 15; Aug. 197
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  • 37
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    Three dimensional beam elements synthesis applications with stress constraints, nonlinear size-stiffness relationships and various size-inertia powers (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 7; Aug. 197
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  • 38
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    Reliability and structural integrity (1976)
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    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.
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  • 39
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    On the role of minicomputers in structural design (1977)
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    Publication Date: 2011-08-17
    Description: Results are presented of exploratory studies on the use of a minicomputer in conjunction with large-scale computers to perform structural design tasks, including data and program management, use of interactive graphics, and computations for structural analysis and design. An assessment is made of minicomputer use for the structural model definition and checking and for interpreting results. Included are results of computational experiments demonstrating the advantages of using both a minicomputer and a large computer to solve a large aircraft structural design problem.
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  • 40
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    Resizing procedure for structures under combined mechanical and thermal loading (1976)
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    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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  • 41
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    Imperfection surveys on a 10-ft-diameter shell structure (1977)
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    Publication Date: 2011-08-17
    Description: The results of an extensive imperfection survey on a 10-ft-diameter integrally stiffened cylindrical shell are presented. The shape of the measured initial imperfections is clearly influenced by details of the shell construction. The modal components of the measured imperfection surface as a function of the circumferential and of the axial wave numbers are calculated. The discrete axial power spectral density functions and the corresponding root-mean-square values of the imperfections are also determined for given circumferential wave numbers. Using the Fourier coefficients of the measured initial imperfections, buckling loads are calculated by solving the nonlinear Donnell-type imperfect shell equations iteratively. The calculated lowest buckling load compares favorably with the values usually recommended for similar shell structures.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 15; July 197
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  • 42
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    A finite element technique for non-deterministic thermal deformation analyses including temperature dependent material properties (1977)
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    Publication Date: 2011-08-17
    Description: A technique utilizing the finite element displacement method is developed for the static analysis of structures subjected to non-deterministic thermal loading in which the material properties, assumed isotropic, are temperature dependent. Matrix equations are developed for the first two statistical moments of the displacements using a third order series expansion for the displacements in terms of the random temperatures. Sample problems are included to demonstrate the range of applicability of the third order series solutions. These solutions are compared with results from Monte Carlo analyses and also, for some problems, with solutions obtained by numerically integrating equations for the statistical properties of the displacements. In general, it is shown that the effect of temperature dependent material properties can have a significant effect on the covariances of the displacements.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering; 11; 6, 19; 1977
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  • 43
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    Forced vibrations of simply supported orthotropic sandwich plates (1977)
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    Publication Date: 2011-08-17
    Description: Force transmissibility, driving-point impedance, and transfer impedance of a simply supported rectangular orthotropic sandwich plate are investigated. The plate is driven by a sinusoidally varying point force either at the plate center or at any arbitrary location. The variation of force transmissibility and impedance with frequency, and the manner in which this is influenced by the various sandwich-plate parameters are studied and presented graphically.
    Keywords: STRUCTURAL MECHANICS
    Type: Acoustical Society of America; vol. 61
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  • 44
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    Effect of longitudinal or inplane deformation and inertia on the large amplitude flexural vibrations of slender beams and thin plates (1976)
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    Publication Date: 2011-08-17
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 49; Dec. 8
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  • 45
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    Symbolic manipulation techniques for vibration analysis of laminated elliptic plates (1977)
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    Publication Date: 2011-08-17
    Description: A computational scheme is presented for the free vibration analysis of laminated composite elliptic plates. The scheme is based on Hamilton's principle, the Rayleigh-Ritz technique and symmetry considerations and is implemented with the aid of the MACSYMA symbolic manipulation system. The MACYSMA system, through differentiation, integration, and simplification of analytic expressions, produces highly-efficient FORTRAN code for the evaluation of the stiffness and mass coefficients. Multiple use is made of this code to obtain not only the frequencies and mode shapes of the plate, but also the derivatives of the frequencies with respect to various material and geometric parameters.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center Proc. of the 1977 MACSYMA Users' Conf. (NASA); p 161-175
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  • 46
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    Surface energy and surface tension at holes and cracks (1975)
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    Publication Date: 2011-08-16
    Description: The concept of surface tension and surface energy of solids was used by Griffith to obtain a criterion for the extension of cracks in brittle materials. Griffith, however, neglected the stresses due to the normal traction at the crack implied by the surface tension. A complete solution to the problem of an elliptic hole in an infinite plate with surface tension loading at the hole is given. Complex potentials are given in closed form in terms of elliptic integrals of the first, second, and third kinds. Stress distributions are studied. For a flat crack, the nature of the singularity at the tip is shown to be radically different from that usually encountered in fracture mechanics. The implications of our analysis for theories of fracture in brittle materials are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 11; Feb. 197
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  • 47
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    Static load-carrying capacity of circular rigid-plastic plates under Gaussian distribution of pressure (1976)
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    Publication Date: 2011-08-16
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Solids and Structures; 12; 8, 19; 1976
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  • 48
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    Large amplitude free vibrations of tapered beams (1976)
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    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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  • 49
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    The computer in shell stability analysis (1975)
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    Publication Date: 2011-08-16
    Description: Some examples in which the high-speed computer has been used to improve the static stability analysis capability for general shells are examined. The fundamental concepts of static stability are reviewed with emphasis on the differences between linear bifurcation buckling and nonlinear collapse. The analysis is limited to the stability of conservative systems. Three examples are considered. The problem of cylinders subjected to bending loads is used as an example to illustrate that a simple structure can have a sufficiently complicated nonlinear behavior to require a computer analysis for accurate results. An analysis of the problems involved in the modeling of stiffening elements in plate and shell structures illustrates the necessity that the analyst recognizes all important deformation modes. The stability analysis of the Skylab structure indicates the size of problems that can be solved with current state-of-the-art capability.
    Keywords: STRUCTURAL MECHANICS
    Type: American Society of Civil Engineers; Journal
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  • 50
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    Boundary-layer effect in panel flutter (1975)
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    Publication Date: 2011-08-16
    Description: The present note shows that if the supersonic Mach number is not too large, an analytical expression can be obtained for the generalized aerodynamic force relating the pressure fluctuation at the surface of a flexible plate to the plate displacement in the presence of an adjacent boundary layer. The low supersonic Mach numbers are the ones of maximum interest since it is in this Mach number region that the boundary layer has the most influence. In this respect, Dowell (1971) has already shown that the presence of a boundary layer causes about a 300% increase in flutter dynamic pressure at a Mach number of about 1.2, while it causes only about a 20% increase at a Mach number of 2.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 13; Sept
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  • 51
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    Fracture angle and strain-energy-density-factor of a crack at hole at an arbitrary angle (1975)
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    Publication Date: 2011-08-16
    Description: For both the maximum stress criterion and strain-energy-density-factor (S) theory, fracture angle (the initial angle of crack growth) is predicted by using opening and sliding mode stress intensity factors. These theoretical predictions are consistent with experimental fracture angles. For the S theory, the crack spreads in the direction of the negative fracture angle in a plane for which S is a minimum. This quantity was obtained analytically. The experimental data of the critical S on plexiglass fracture specimens remains essentially constant.
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    Structural optimization via a design space hierarchy (1976)
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    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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    Instrumental variables algorithm for modal parameter identification in flutter testing (1978)
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    Publication Date: 2011-08-17
    Description: The paper is concerned with the task of estimating modal parameters from system response measurement in aircraft flutter testing. A frequency-domain derivation of an instrumental-variables algorithm is presented for a linear time-invariant dynamic system of order n. Basically, this algorithm fits a set of poles and zeros to the measured transfer function. An illustrative example is provided regarding the application of the algorithm to aeroelasticity testing. It is shown that the algorithm can be implemented for on-line data reduction with a microcomputer-based analysis system. By using instrumental variables the sensitivity of the modal parameter estimates to noise in the system-response measurements is reduced greatly. The algorithm is expected to be a powerful and valuable tool for on-line estimation of modal parameters in flutter testing and should be useful in control system and structural dynamics tests.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 16; Aug. 197
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  • 54
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    Trends in aerospace structures (1978)
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    Publication Date: 2011-08-17
    Description: Recent developments indicate that there may soon be a revolution in aerospace structures. Increases in allowable operational stress levels, utilization of high-strength, high-toughness materials, and new structural concepts will highlight this advancement. Improved titanium and aluminum alloys and high-modulus, high-strength advanced composites, with higher specific properties than aluminum and high-strength nickel alloys, are expected to be the principal materials. Significant advances in computer technology will cause major changes in the preliminary design cycle and permit solutions of otherwise too-complex interactive structural problems and thus the development of vehicles and components of higher performance. The energy crisis will have an impact on material costs and choices and will spur the development of more weight-efficient structures. There will also be significant spinoffs of aerospace structures technology, particularly in composites and design/analysis software.
    Keywords: STRUCTURAL MECHANICS
    Type: Astronautics and Aeronautics; 16; July-Aug
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    Needs and trends in structural dynamics (1978)
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    Publication Date: 2011-08-17
    Description: The paper discusses dynamic analyses and testing of aerospace vehicles and the application of such analyses and testing to nonaerospace fields. Items covered in the section on dynamic analyses of aerospace vehicles include self-induced and forced oscillatory loads, approaches to dynamic modeling and analysis, nonlinear analyses, and integrated dynamics design and optimization. Items covered in the section on the dynamic testing of aerospace vehicles include integrated test philosophy, test facilities, and ways of improving performance and reducing costs. The nonaerospace applications that are discussed include ground and water transportation, medicine, and nuclear power plants.
    Keywords: STRUCTURAL MECHANICS
    Type: Astronautics and Aeronautics; 16; July-Aug
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    Application of a trigonometric finite difference procedure to numerical analysis of compressive and shear buckling of orthotropic panels (1978)
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    Publication Date: 2011-08-17
    Description: A numerical analysis developed for the buckling of rectangular orthotropic layered panels under combined shear and compression is described. This analysis uses a central finite difference procedure based on trigonometric functions instead of using the conventional finite differences which are based on polynomial functions. Inasmuch as the buckle mode shape is usually trigonometric in nature, the analysis using trigonometric finite differences can be made to exhibit a much faster convergence rate than that using conventional differences. Also, the trigonometric finite difference procedure leads to difference equations having the same form as conventional finite differences; thereby allowing available conventional finite difference formulations to be converted readily to trigonometric form. For two-dimensional problems, the procedure introduces two numerical parameters into the analysis. Engineering approaches for the selection of these parameters are presented and the analysis procedure is demonstrated by application to several isotropic and orthotropic panel buckling problems. Among these problems is the shear buckling of stiffened isotropic and filamentary composite panels in which the stiffener is broken. Results indicate that a break may degrade the effect of the stiffener to the extent that the panel will not carry much more load than if the stiffener were absent.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 9; July 197
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    Effect of geometric nonlinearity on the free flexural vibrations of moderately thick rectangular plates (1978)
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    Publication Date: 2011-08-17
    Description: The effect of geometric nonlinearity on the free flexural vibrations of moderately thick rectangular plates is studied in this paper. Finite element formulation is employed to obtain the non-linear to linear period ratios for some rectangular plates. A conforming finite element of rectangular shape wherein the effects of shear deformation and rotatory inertia are included, is developed and used for the analysis. Results are presented for both simply supported and clamped boundary conditions.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 9; Nov. 197
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    Finite dynamic element formulation for a plane triangular element (1979)
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    Publication Date: 2011-08-17
    Description: Higher order correction terms for the stiffness and inertia matrices associated with a triangular plane stress-strain finite dynamic element are developed in detail. Numerical results are presented which indicate that the adoption of these matrices along with a suitable quadratic matrix eigenproblem solver effects a significant economy in the free vibration solution of structure when compared with the analysis based on the usual finite element procedure. Finally, a FORTRAN IV computer program listing of the various relevant matrices is given.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering; 14; 10, 1; 1979
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    Doubly-curved variable-thickness isoparametric heterogeneous finite element (1977)
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    Publication Date: 2011-08-17
    Description: This paper describes an element streamlined for the analysis of doubly-curved, variable-thickness structural components and illustrates its effective application to vibration and static problems. The element is isoparametric, doubly-curved, thin-shell and triangular with variable thickness and accounts for anisotropic, inhomogeneous elastic material behavior. The element has six nodes (three corner and three mid-side) with five degrees-of-freedom (DOF) per node - three translations and two rotations. Quadratic isoparametric interpolation polynomials are used to express the element geometry and displacement variables in terms of corresponding nodal variables.
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    Stall flutter and nonlinear divergence of a two-dimensional flat plate wing (1976)
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    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.
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    Hamilton's principle - Finite-element methods and flexible body dynamics (1977)
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    Publication Date: 2011-08-17
    Description: A variational formulation is given for the equations of motion for an unconstrained elastic body, and Hamilton's principle is used to derive the equations of motion and deformation of the body. Finite-element approximations are developed for these dynamical equations with respect to a body axis system satisfying the mean axis conditions. The free-body influence matrix for the body then is developed in terms of the finite-element model parameters.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 15; Dec. 197
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    Strain gage calibration of a complex wing (1977)
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    Publication Date: 2011-08-17
    Description: Modern complex structural arrangements have complicated the task of measuring flight loads with calibrated strain gages. This paper examines the use of a relatively simple structural model to characterize the load responses of strain gages located on various spars of a delta wing. Strains measured during a laboratory load calibration of a wing structure are compared with calculations obtained from a simplified NASA structural analysis (NASTRAN) model. Calculated and measured influence coefficient plots that show the shear, bending, and torsion characteristics of typical strain-gage bridges are presented. Typical influence coefficient plots are given for several load equations to illustrate the derivation of the equations from the component strain-gage bridges. A relatively simple structural model was found to be effective in predicting the general nature of strain distributions and influence coefficient plots. The analytical processes are shown to be useful in obtaining a good load calibration. The analytical processes cannot, however, be used in lieu of an actual load calibration of an aircraft wing.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Aircraft; 14; Dec. 197
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    Scaling a discrete structural model to match measured modal frequencies (1977)
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    Publication Date: 2011-08-17
    Description: The structure modification problem, where the computer model of a structure is to be upgraded on the basis of experimental measurements of normal mode frequencies, is approached by the modal energy concept. The modes for correlation with test data are selected on the basis of relative strain energy participation. The resulting procedure can be viewed as an extension of White's (1972) method. Its advantage lies in that both the number and choice of structural parameters to be varied in the modification are arbitrary.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 15; Nov. 197
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    Mode I stress intensity factors for round compact specimens (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Mode I stress intensity factors were computed for round compact specimens by the boundary collocation method. Results are presented for ratios At/R0 in the range 0.3 to 0.8, where At is the distance from the specimen center to the crack tip for a specimen of diameter 2R0.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Testing and Evaluation; 5; Nov. 197
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    Design of composite structural components (1975)
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    Publication Date: 2011-08-16
    Description: Aspects related to the evolution of design are examined. A schematic of the evolution of the design objective and a schematic of designing a structural component from fiber composites are presented. A description of conventional design procedures is given, taking into account design handbooks, design guides, various sources of design information, and typical design data. Optimization methods are discussed, giving attention to parametric studies, the structural index method, aspects of structural synthesis, and questions of simultaneous material and structural design optimization.
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    Experimental characterization of composites (1975)
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    Publication Date: 2011-08-16
    Description: The experimental characterization for composite materials is generally more complicated than for ordinary homogeneous, isotropic materials because composites behave in a much more complex fashion, due to macroscopic anisotropic effects and lamination effects. Problems concerning the static uniaxial tension test for composite materials are considered along with approaches for conducting static uniaxial compression tests and static uniaxial bending tests. Studies of static shear properties are discussed, taking into account in-plane shear, twisting shear, and thickness shear. Attention is given to static multiaxial loading, systematized experimental programs for the complete characterization of static properties, and dynamic properties.
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    Lattice theory of three-dimensional cracks (1976)
    In:  Other Sources
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    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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  • 68
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    Symmetric stiffness matrix for incompressible hyperelastic materials (1976)
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    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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  • 69
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    Dynamic response of membranes with finite elements (1976)
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    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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  • 70
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    Disjoint design spaces in the optimization of harmonically excited structures (1976)
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    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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  • 71
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    Simplified contact analysis (1978)
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    Publication Date: 2011-08-17
    Description: A simple and straightforward method for calculating the elastic deformation at the center of contact between two solids with different radii of curvature is proposed instead of the conventional contact deformation analysis for ball bearings, gears, and cams, which usually involves tedious iterative procedures or the use of design charts. Ellipticity of the contact is approximated from a least-squares power fit. Simplified expressions are derived which allow rapid calculation of deformation from the material properties and geometry of the contacting elements.
    Keywords: STRUCTURAL MECHANICS
    Type: Machine Design; 50; Mar. 9
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  • 72
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    Finite element microscopic stress analysis of cracked composite systems (1978)
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    Publication Date: 2011-08-17
    Description: This paper considers the stress concentration problems of two types of cracked composite systems: (1) a composite system with a broken fiber (a penny-shaped crack problem), and (2) a composite system with a cracked matrix (an annular crack problem). The cracked composite systems are modeled with triangular and trapezoidal ring finite elements. Using NASTRAN (NASA Structural Analysis) finite element computer program, the stress and deformation fields in the cracked composite systems are calculated. The effect of fiber-matrix material combination on the stress concentrations and on the crack opening displacements is studied.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Composite Materials; 12; Jan. 197
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  • 73
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    Analysis and testing of adhesive bonds (1977)
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    Publication Date: 2011-08-17
    Description: An adhesive fracture mechanics approach is described with reference to the identification and design of the best tests for evaluating a given adhesive, the definition of the most meaningful fundamental parameters by which adhesives might be characterized, and the application of these parameters to the design of joints and to the prediction of their performance. Topics include standard adhesive test techniques, the theory of adhesive fracture, and adhesive fracture energy tests. Analytical methods and computer techniques for adhesive bonding, chemical and physical aspects of adhesive fracture, and specific applications and aspects of adhesive fracture mechanics are discussed.
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  • 74
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    Analysis of beam-like lattice trusses (1979)
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    Publication Date: 2011-08-17
    Description: A simple procedure is presented for predicting the thermoelastic and free vibration responses of large repetitive beam-like trusses. The procedure is based on replacing the original lattice structure by an equivalent continuum beam model and obtaining closed-form (exact) solutions for the beam model. The equivalent beam model accounts for warping and shear deformation in the plane of the cross-section and is characterized by its thermoelastic strain and kinetic energies, from which the equations of motion and constitutive relations can be derived. The high accuracy of the results obtained by the proposed approach is demonstrated by means of numerical examples.
    Keywords: STRUCTURAL MECHANICS
    Type: Computer Methods in Applied Mechanics and Engineering; 20; Oct. 197
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  • 75
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    Some observations regarding the statistical determination of stress rupture regression lines (1979)
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    Publication Date: 2011-08-17
    Description: Observations concerning the statistical evaluation of creep data are presented. Methods currently employed in the determination of stress rupture regression lines can result in conflicting and necessarily invalid results. Anomalous behavior is principally associated with the selection of the dependent variable. However, it is the least squares method of curve fitting which introduces regression bias. Methods to improve the validity of least squares regressions are suggested.
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  • 76
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    Buckling of rotating beams (1979)
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    Publication Date: 2011-08-17
    Description: The stability of a beam subjected to compressive centrifugal forces arising from steady rotation about an axis which does not pass through the clamped end of the beam is analyzed to determine the critical rotational speeds for buckling in the inplane and out-of-plane directions. The differential equations of motion are solved numerically using an integrating matrix method in combination with an eigenanalysis to determine the eigenvalues from which stability is assessed. The results clarify several differences which have been identified in the literature relating to the proper behavior of the critical rotational speed for buckling as the radius of rotation of the clamped end of the beam is reduced.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Mechanical Sciences; 21; 12, 1; 1979
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  • 77
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    Simple spline-function equations for fracture mechanics calculations (1979)
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    Publication Date: 2011-08-17
    Description: The paper presents simple spline-function equations for fracture mechanics calculations. A spline function is a sequence of piecewise polynomials of degree n greater than 1 whose coefficients are such that the function and its first n-1 derivatives are continuous. Second-degree spline equations are presented for the compact, three point bend, and crack-line wedge-loaded specimens. Some expressions can be used directly, so that for a cyclic crack propagation test using a compact specimen, the equation given allows the cracklength to be calculated from the slope of the load-displacement curve. For an R-curve test, equations allow the crack length and stress intensity factor to be calculated from the displacement and the displacement ratio.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 15; Oct. 197
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  • 78
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    A quarter-century of progress in the development of correlation and extrapolation methods for creep rupture data (1979)
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    Publication Date: 2011-08-17
    Description: Developments in the analysis of creep-rupture data are reviewed with particular reference to time temperature relations for the correlation and extrapolation of creep and stress rupture data, the minimum commitment method, and successive regression methods. Some contributions to the development of time-temperature parameters are noted.
    Keywords: STRUCTURAL MECHANICS
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  • 79
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    Wave propagation in transversely impacted composite laminates (1979)
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    Publication Date: 2011-08-17
    Description: An experimental study was conducted to determine the wave-propagation characteristics, transient strains and residual properties of unidirectional and angle-ply boron/epoxy and graphite/epoxy laminates impacted with silicon-rubber projectiles at velocities up to 250 m/sec. Results include the following: (1) the predominant wave is the flexural wave propagating at different velocities in different directions; (2) peak strains and strain rates in the transverse to the (outer) fiber direction are much higher than those in the direction of the fibers; (3) strain rates up to 640/sec were measured; and (4) unidirectional laminates under impact showed appreciable modulus and strength degradation in the direction transverse to fibers.
    Keywords: STRUCTURAL MECHANICS
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  • 80
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    Analysis of misalignment in the tension test (1979)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Many experimenters fail to appreciate the significance of test system alignment during a tensile test. Poor alignment can increase data scatter and significantly influence some of the test results. In this paper a comprehensive analytical study of the misalignment problem in the plastic strain range is presented and errors caused by misalignment estimated. The results show that the stress-strain curve is not significantly affected by misalignment. However, the strains at the outermost fibers of the specimen cross-section are strongly affected by misalignment. Therefore, the effect of misalignment is most important when properties sensitive to local strain concentrations are being investigated.
    Keywords: STRUCTURAL MECHANICS
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  • 81
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    Mode I analysis of a face cracked plate subjected to rotationally constrained end displacements (1978)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 14; Dec. 197
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  • 82
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    Effect of crack size on the natural frequencies of a cracked plate (1978)
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    Publication Date: 2011-08-17
    Description: Results are presented for a finite element modal analysis of a centrally cracked rectangular plate made of linearly elastic material. The objective is to assess the effect of crack size on the natural vibration frequencies of the cracked plate. Only the in-plane vibration modes are studied. The results presented are finite-element mesh-size dependent. Namely, shrinking the mesh size, especially in the crack tip region, would change the magnitudes of the natural frequencies, and the trends would be the same as shown in the present note.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 14; Oct. 197
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  • 83
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    The general solution to the classical problem of the finite Euler-Bernoulli beam (1978)
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    Publication Date: 2011-08-17
    Description: An analytical solution is obtained for the problem of free and forced vibrations of a finite Euler-Bernoulli beam with arbitrary (partially fixed) boundary conditions. The effects of linear viscous damping, Winkler foundation, constant axial tension, a concentrated mass, and an arbitrary forcing function are included in the analysis. No restriction is placed on the values of the parameters involved, and the solution presented here contains all cited previous solutions as special cases.
    Keywords: STRUCTURAL MECHANICS
    Type: Zeitschrift fuer angewandte Mathematik und Physik; 29; July 25
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  • 84
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    Nonlinear behavior of circular plates with work hardening (1978)
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    Publication Date: 2011-08-17
    Description: Tests were performed on two simply supported plates of aluminum alloy 2024-0, under a central concentrated load, with peak deflections up to 2.6 times the thickness. The load was provided by a small-diameter hard-steel rod. The plates had diameter-to-thickness ratios (D/h) of 20 and 41. Measurements were made of load, deflections and strains; membrane and bending strains were calculated from the test data. The test data are presented in comparison with theoretical predictions generated by the finite-element-computer code PLANS, which includes material and geometric nonlinearities. The theoretical prediction was excellent for deflections, and generally good for strains, when the central force was represented by a line load around the loading rod's contact circle.
    Keywords: STRUCTURAL MECHANICS
    Type: Experimental Mechanics; 18; Aug. 197
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    Substructuring techniques - Status and projections (1978)
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    Publication Date: 2011-08-17
    Description: Substructuring techniques are examined in terms of their application to structural analysis. Attention is given to multilevel substructuring algorithms, hypermatrix and other sparse matrix schemes, automated design systems, and elasto-plastic problems. Applications include use with computing hardware such as CDC STAR-100 and minicomputer systems.
    Keywords: STRUCTURAL MECHANICS
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    Non-linear dynamic response of a wind turbine blade (1979)
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    Publication Date: 2011-08-17
    Description: The paper outlines the nonlinear dynamic analysis of an isolated three-degree flap-lag-feather wind turbine blade under a gravity field and with shear flow. Lagrangian equations are used to derive the nonlinear equations of motion of blade for arbitrarily large angular deflections. The limit cycle analysis for forced oscillations and the determination of the principal parametric resonance of the blade due to periodic forces from the gravity field and wind shear are performed using the harmonic balance method. Results are obtained first for a two-degree flap-lag blade, then the effect of the third degree of freedom (feather) is studied. The self-excited flutter solutions are obtained for a uniform wind and with gravity forces neglected. The effects of several parameters on the blade stability are examined, including coning angle, structural damping, Lock number, and feather frequency. The limit cycle flutter solution of a typical configuration shows a substantial nonlinear softening spring behavior.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 63; Mar. 22
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    Recent finite element studies in plasticity and fracture mechanics (1979)
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    Publication Date: 2011-08-17
    Description: The paper reviews recent work on fundamentals of elastic-plastic finite-element analysis and its applications to the mechanics of crack opening and growth in ductile solids. The presentation begins with a precise formulation of incremental equilibrium equations and their finite-element forms in a manner valid for deformations of arbitrary magnitude. Special features of computational procedures are outlined for accuracy in view of the near-incompressibility of elastic-plastic response. Applications to crack mechanics include the analysis of large plastic deformations at a progressively opening crack tip, the determination of J integral values and of limitations to J characterizations of the intensity of the crack tip field, and the determination of crack tip fields in stable crack growth.
    Keywords: STRUCTURAL MECHANICS
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  • 88
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    Stress-intensity factors for a wide range of semi-elliptical surface cracks in finite-thickness plates (1979)
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    Publication Date: 2011-08-17
    Description: Surface cracks are among the more common flaws in aircraft and pressure vessel components. Several calculations of stress-intensity factors for semi-elliptical surface cracks subjected to tension have appeared in the literature. However, some of these solutions are in disagreement by 50-100%. In this paper, stress-intensity factors for shallow and deep semi-elliptical surface cracks in plates subjected to tension are presented. To verify the accuracy of the three-dimensional finite-element models employed, convergence was studied by varying the number of degrees of freedom in the models from 1500 to 6900. The 6900 degrees of freedom used here were more than twice the number used in previously reported solutions. Also, the stress-intensity variations in the boundary-layer region at the intersection of the crack with the free surface were investigated.
    Keywords: STRUCTURAL MECHANICS
    Type: Engineering Fracture Mechanics; 11; 4, 19; 1979
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  • 89
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    Automated multi-level substructuring for Sperry's version of NASTRAN (1977)
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    Publication Date: 2016-06-07
    Description: Automated multilevel substructuring was successfully implemented in the Sperry version of NASTRAN. The development was achieved with a minimum effort; only seven modules and fourteen new routines were added. Approximately forty subroutines were modified and four new user cards addeded to NASTRAN. Significant features of the new capability include: multilevel substructuring; up to 128 superelements; up to 456 boundary grid points per superelement; up to 9 user superelement files, each with multi-reel or disc option; and data storage for one or more superelements per user file.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA, Washington 6th NASTRAN (R) Users' Colloq.; p 133-154
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    Structural model integrity (1977)
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    Publication Date: 2016-06-07
    Description: Many of the practical aspects and problems of ensuring the integrity of a structural model are discussed, as well as the steps which have been taken in the NASTRAN system to assure that these checks can be routinely performed. Model integrity as used applies not only to the structural model but also to the loads applied to the model. Emphasis is also placed on the fact that when dealing with substructure analysis, all of the checking procedures discussed should be applied at the lowest level of substructure prior to any coupling.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA, Washington 6th NASTRAN (R) Users' Colloq.; p 93-104
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    Finite element solutions of free surface flows (1977)
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    Publication Date: 2016-06-07
    Description: A procedure is presented for using NASTRAN to determine the flow field about arbitrarily shaped bodies in the presence of a free surface. The fundamental unknown of the problem is the velocity potential which must satisfy Laplace's equation in the fluid region. Boundary conditions on the free surface may involve second order derivatives in space and time. In cases involving infinite domains either a tractable radiation condition is applied at a truncated boundary or a series expansion is used and matched to the local finite elements. Solutions are presented for harmonic, transient, and steady state problems and compared to either exact solutions or other numerical solutions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA, Washington 6th NASTRAN (R) Users' Colloq.; p 27-52
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  • 92
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    The automated multi-stage substructuring system for NASTRAN (1975)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: The substructuring capability developed for eventual installation in Level 16 is now operational in a test version of NASTRAN. Its features are summarized. These include the user-oriented, Case Control type control language, the automated multi-stage matrix processing, the independent direct access data storage facilities, and the static and normal modes solution capabilities. A complete problem analysis sequence is presented with card-by-card description of the user input.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 571-591
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    Analysis of nonlinear structures via mode synthesis (1975)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: An effective procedure for NASTRAN was developed that permits any number of substructures of any size to be synthesized for the purpose of developing normal modes of vibration of the complete structural system. The technique is extended to permit modal transient analysis of the subdivided system. This latter procedure permits the use of NASTRAN's ability to include nonlinear forces in the problem. The five-phase process is accomplished using standard NASTRAN rigid formats with problem-independent alter packages and DMAP sequences.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 341-360
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    On eigenvectors of multiple eigenvalues obtained in NASTRAN (1975)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: In the case of nonmultiple eigenvalues, each of the three real eigenvalue extraction methods available in NASTRAN will, for a given type of normalization, give essentially the same eigenvectors, but this is not so in the case of multiple eigenvalues. This discrepancy is explained and illustrated by considering the example of a NASTRAN demonstration problem that has both multiple and nonmultiple eigenvalues.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 285-300
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    NASTRAN solutions of problems described by simultaneous parabolic differential equations (1975)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: NASTRAN solution techniques are shown for a numerical analysis of a class of coupled vector flow processes described by simultaneous parabolic differential equations. To define one physical problem type where equations of this form arise, the differential equations describing the coupled transfers of heat and mass in mechanical equilibrium with negligible mass average velocity are presented and discussed. Also shown are the equations describing seepage when both electrokinetic and hydrodynamic forces occur. Based on a variational statement of the general problem type, the concepts of scalar transfer elements and parallel element systems are introduced. It is shown that adoptation of these concepts allows the direct use of NASTRAN's existing Laplace type elements for uncoupled flow (the heat transfer elements) for treating multicomponent coupled transfer. Sample problems are included which demonstrate the application of these techniques for both steady-state and transient problems.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: Users' Experiences; p 65-90
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    NASTRAN maintenance and enhancement experiences (1975)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: The current capability is described which includes isoparametric elements, optimization of grid point sequencing, and eigenvalue routine. Overlay and coding errors were corrected for cyclic symmetry, transient response, and differential stiffness rigid formats. Error corrections and program enhancements are discussed along with developments scheduled for the current year and a brief description of analyses being performed using the program.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences (SEE N75-31485 22-39)
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    Understanding the NASTRAN structural plotter (1975)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: Functions of the plotting hardware and the operations performed by the NASTRAN structural plotter are summarized to provide the user an insight into how the program works. The processing performed in response to each plot command is described and the interrelationships of the various parameters are explained. To assist in the effective and efficient utilization of the system, examples are provided which also illustrate several not yet documented capabilities of the Level 16 structural plotter.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 475-492
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  • 98
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    The impact of fourth generation computers on NASTRAN (1975)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The impact of 'fourth generation' computers (STAR 100 or ILLIAC 4) on NASTRAN is considered. The desired characteristics of large programs designed for execution on 4G machines are described.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: Users' Experiences; p 431-447
    Format: application/pdf
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  • 99
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    NASTRAN thermal analyzer status, experience, and new developments (1975)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The unique finite element based NASTRAN Thermal Analyzer originally developed as a general purpose heat transfer analysis incorporated into the NASTRAN system is described. The current status, experiences from field applications, and new developments are included.
    Keywords: STRUCTURAL MECHANICS
    Type: NASTRAN: User's Experiences; p 523-528
    Format: application/pdf
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  • 100
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    Recent improvements to BANDIT (1975)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The NASTRAN preprocessor BANDIT, which improves NASTRAN's computer efficiency by resequencing grid point labels for reduced matrix bandwidth is described. The addition of (1) the Gibbs-Poole-Stockmeyer (GPS) algorithm, and (2) the user option to reduce matrix profile rather than matrix bandwidth is also described. It is shown that, compared to the Cuthill-McKee algorithm on which BANDIT was originally based, GPS is faster and achieves similar results. Current capabilities and options of BANDIT are summarized.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 511-521
    Format: application/pdf
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