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  • General Chemistry  (1,159)
  • Cell & Developmental Biology  (701)
  • STRUCTURAL MECHANICS
  • ddc:330
  • 1980-1984  (2,072)
  • 1970-1974
  • 1982  (2,072)
Collection
Keywords
Publisher
Years
  • 1980-1984  (2,072)
  • 1970-1974
Year
  • 1
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    Space shuttle solid rocket booster water entry cavity collapse loads (1982)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: Solid rocket booster cavity collapse flight measurements included external pressures on the motor case and aft skirt, internal motor case pressures, accelerometers located in the forward skirt, mid-body area, and aft skirt, as well as strain gages located on the skin of the motor case. This flight data yielded applied pressure longitudinal and circumferential distributions which compare well with model test predictions. The internal motor case ullage pressure, which is below atmospheric due to the rapid cooling of the hot internal gas, was more severe (lower) than anticipated due to the ullage gas being hotter than predicted. The structural dynamic response characteristics were as expected. Structural ring and wall damage are detailed and are considered to be attributable to the direct application of cavity collapse pressure combined with the structurally destabilizing, low internal motor case pressure.
    Keywords: STRUCTURAL MECHANICS
    Type: Shock and Vibration Inform. Center The Shock and Vibration Bull., No. 52. Part 2; p 21-26
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  • 2
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    A study of component design loads due to dynamic environment (1982)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The random vibration of the components of the space shuttle causing internal cargo bay acoustic impingement on the payload was investigated. The import factors to be considered in the design of acoustically loaded structures are the prediction of acoustic environment, prediction of structural response to this environment, and to determine the effect of the response on the structural strength requirements. Two basic responses were analyzed. The primary structure response due to random vibration is first analyzed. The output of primary structure response is used as an input to the secondary structure to calculate the component response.
    Keywords: STRUCTURAL MECHANICS
    Type: Alabama Univ. in Huntsville The 1981 NASA(ASEE Summer Fac. Fellowship Program; 12 p
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  • 3
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    Surface contour of a biaxially strained, doubly curved antenna reflective mesh (1982)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The elastic membrane equations which describe the deflection of a biaxially tensioned reflective mesh from an idealized surface were developed and solved. The conditions of equilibrium of the forces acting on a membrane element furnish equations which may be used to solve a variety of problems. Configurations considered include continuous, as well as incremental mesh attachment to structural members to form shapes which are approximately parabolic or spherical.
    Keywords: STRUCTURAL MECHANICS
    Type: Alabama Univ. in Huntsville The 1981 NASA(ASEE summer Fac. Fellowship Program; 11 p
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  • 4
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    Determination of normal modes from measured complex modes (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: A technique is presented for computing a set of normal modes from a set of measured complex modes. The number of elements in the modal vectors, which is equal to the number of measurements, can be larger than the number of modes under consideration. It is also shown that the practice of normal mode approximation to complex modes can lead to very large errors when the modes are too complex. A numerical example and a simulated experiment illustrate the concepts discussed and support the theory presented.
    Keywords: STRUCTURAL MECHANICS
    Type: Shock and Vibration Inform. Center The Shock and Vibration Bull., No. 52. Part 5; p 13-17
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  • 5
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    Required developments in structural dynamics (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The finite element method, modal component synthesis, and the use of fast Fourier transformation were key developments in structural dynamics in the past 15 to 20 years. Current areas requiring additional effort include: (1) the correct calculation of modal shape and natural frequencies for complex structures; (2) the correlation of math models with test data; (3) the establishment of a criteria for "goodness" of the correlation between analysis and test; (4) the selection of the correct displacement functions when using computer programs for modal synthesis; (5) accuracy of response calculations; and (6) the inverse problem of determining the force problem from the response data. Trends identified include the use of distributed computing, greater reliance on analysis, and the possible use of artificial intelligence techniques, or some way of feeding back information, to provide solution guidance to engineers.
    Keywords: STRUCTURAL MECHANICS
    Type: Shock and Vibration Inform. Center The Shock and Vibration Bull., No. 52. Part 1; p 49-54
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  • 6
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    The usage of substructuring analyses in the Get Away Special (GAS) program (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The use of automatic multi-stage substructing analysis is demonstrated for a hypothetical case of a GAS container supported by structural channels with a simulated experimental package inside the container. The GAS program purpose is stated and potential candidate structures to support experimental packages are discussed. The GAS container model and the substructuring analysis capabilities of NASTRAN make it possible to study the experiments inside the container as well as the design constraints resulting from the support structures holding the containers. The use of substructuring in the GAS program could be an important factor in increasing the number of flight opportunities.
    Keywords: STRUCTURAL MECHANICS
    Type: Georgia Univ. 10th NASTRAN User's Colloq.; p 204-215
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  • 7
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    A mixed formulation finite element for linear thin shell analysis (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: An eight node curved thin shell slement was tested. The element is based on the degenerate solid concept and the mixed formulation with the independent inplane and transverse shear strains. The number of unknown parameters in the assumed strains is chosen to alleviate the spurious constaining or locking effect. It is indicated that for a pinched cylindrical shell with diaphragmed ends and fixed ends the present element shows good performance.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 219-228
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  • 8
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    Application of a boundary element method to the study of dynamical torsion of beams (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: During dynamic torsion of beam elements, consideration of nonuniform warping effects involves a more general technical formulation then that of Saint-Venant. Nonclassical torsion constants appear in addition to the well known torsional rigidity. The adaptation of the boundary integral element method to the calculation of these constants for general section shapes is described. The suitability of the formulation is investigated with some examples of thick as well as thin walled cross sections.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 129-139
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  • 9
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    Application of the reduced basis method to nonlinear transient thermal analysis (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: An effort to apply the reduced basis method to nonlinear transient thermal analysis is described. The method combines the classical Rayleigh-Ritz and modal superposition techniques with contemporary finite element methods to retain modeling versatility as the degrees of freedom in a problem are reduced. The essence of the method is to use a few thermal modes from eigenvalue analyses as basis vectors to represent the temperature response for a given thermal problem similar to the use of vibration modes to represent displacements in a dynamic response problem. Approximate temperature distributions were obtained using the reduced basis method for a small section of the Shuttle Orbiter lower wing undergoing reentry heating. Good agreement was obtained between the reduced basis method solutions and full system solutions with reductions in the degrees of freedom of up to a factor of four. The good agreement indicates the reduced basis method has the potential for significant reduction in computing effort for thermal analysis; however, considerable work remains to determine techniques for selecting the type and number of basis vectors needed for approximate solutions to more complex transient thermal problems.
    Keywords: STRUCTURAL MECHANICS
    Type: Res. in Struct. and Solid Mech., 1982; p 49-65
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  • 10
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    Approximate analysis of postbuckled through-width delaminations (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: (Previously announced in STAR as N81-27202)
    Keywords: STRUCTURAL MECHANICS
    Type: Composites Technology Review; 4; Fall 198
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  • 11
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    Prediction of transonic flutter for a supercritical wing by modified strip analysis (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: (Previously cited in issue 12, p. 2022, Accession no. A81-29471)
    Keywords: STRUCTURAL MECHANICS
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  • 12
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    Evaluation and reduction of errors induced by the Guyan transformation (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The Guyan reduction refers to a method used to reduce the number of degrees of freedom in a structural model for dynamic analysis. Experience shows that, if the method is properly employed, then this reduction method does in fact provide a "reasonably" accurate approximation of the dynamic characteristics of the unreduced model. A method that provides an accurate estimate of the error in each mode of the reduced eigenvalue problem and, in addition, gives first order correction terms that greatly improve the accuracy of the eigenvectors and eigenvalues is presented. The method is demonstrated by standard COSMIC NASTRAN DAMP alters to rigid format 3, real normal mode analysis. Comparative computer time of modal extraction versus error analysis is discussed for the VAX-11/780 version of COSMIC NASTRAN.
    Keywords: STRUCTURAL MECHANICS
    Type: 10th NASTRAN User's Colloq.; p 233-248
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  • 13
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    Improving a NASTRAN dynamic model with test data using LINWOOD (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The concept of expressing test modes as a linear combination of analytical modes was applied to the prediction of corrective terms in math model mass and stiffness. Test data for the Space Shuttle quarter scale solid rocket booster were analyzed by this method and significant improvements in frequency and mode shap correlation are noted. The applicability of the method is demonstrated.
    Keywords: STRUCTURAL MECHANICS
    Type: Georgia Univ. 10th NASTRAN User's Colloq.; p 74-86
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  • 14
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    Solution of axisymmetric fluid structure interaction problems with NASTRAN (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The solution of axisymmetric acoustic fluid structure interaction problems, employing the NASTRAN computer program is presented. A previously developed 3-D Cartesian Coordinates pressure element formulation is adapted especially for axisymmetric elements. Analogous to the 3-D Cartesian Coordinate predecessor, the fluid portion of the problem is modeled with finite elements wherein one of the displacement components serves as a dummy variable for the pressure unknowns. Two alternatives for implementation of the analogy are presented: (1) an approximate method by which dummy values of G, and nu are used to approximately invoke the analogy wherein the accuracy of the approximation is made as close as desired to the proper analogy within an arbitrary small parameter epsiton; (2) an exact method whereby the NASTRAN FORTRAN coding is slightly changed to invoke the analogy exactly. Comparison of the finite element solution to the exact solution to the same problem is given.
    Keywords: STRUCTURAL MECHANICS
    Type: Georgia Univ. 10th NASTRAN User's Colloq.; p 87-111
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  • 15
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    Recent developments of NASTRAN pre- amd post-processors: Response spectrum analysis (RESPAN) and interactive graphics (GIFTS) (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Two specific NASTRAN preprocessors and postprocessors are examined. A postprocessor for dynamic analysis and a graphical interactive package for model generation and review of resuls are presented. A computer program that provides response spectrum analysis capability based on data from NASTRAN finite element model is described and the GIFTS system, a graphic processor to augment NASTRAN is introduced.
    Keywords: STRUCTURAL MECHANICS
    Type: 10th NASTRAN User's Colloq.; p 19-44
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  • 16
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    Recent improvements and enhancements to NASTRAN (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Several improvements and enhancements recently made to NASTRAN are described. Some of the more important features are: streamlined rigid formats; improved rigid formats; changes related to plotting; checking of required PARAM bulk data cards; checkpoint/restart capability; unsorted and sorted bulk data deck echo; automatic output of the DMAP source listing; elimination of link switching caused by use of utility modules; paging the NASTRAN output; processing of mixed record data blocks by INPUT2/OUTPUT2 modules; module execute flag included in the OSCAR listing; and use of the multiple XDMAP cards in the DMAP. It is concluded that these changes increase the usefulness of the program.
    Keywords: STRUCTURAL MECHANICS
    Type: Georgia Univ. 10th NASTRAN User's Colloq.; p 12-17
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  • 17
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    Ultrasonic measurement of axial stress (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The theory of acoustic propagation in strained media is examined, with particular emphasis on rod (bolt) geometries. The continuous wave (CW) approach is the basis of the study, and the theory is developed from a frequency domain analysis standpoint in order to obtain an applied stress/normalized frequency shift relationship. CW measurements may be influenced by such factors as propagation effects, mode conversion, frequency, material properties, and geometry. After the first loading cycle, axial stress measurements for a preloading with an initial frequency of 4.995 36 MHz dropped to 4.989 19 MHz, indicating a 6.17 kHz change. CW and pseudo-CW ultrasonic techniques are found to be reliable for axial stress measurements, and acoustic attenuation measurements correlated to residual stress fields may possibly involve transducer phase cancellation. It is thus concluded that signal drop is an artifact of the transducer directivity, rather than an actual acoustic power decrease.
    Keywords: STRUCTURAL MECHANICS
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  • 18
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    Extended range stress intensity factor expressions for chevron-notched short bar and short rod fracture toughness specimens (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 19; July 198
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  • 19
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    Crack displacements for J/I/ testing with compact specimens (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The suggestion is made that the standard compact specimen (with opening displacement measured at the crack mouth) may be entirely suitable for J-integral determinations if a very simple conversion factor is used. Experimental determination of J-integral values requires the measurement of displacements at the points of load application. For the compact specimen this is a difficult task. On the basis of studies reported by Newman (1979) and Fisher and Buzzard (1980), it is suggested that for any J-based test the standard compact specimen can be used. A very good approximation to the load point displacement (within 3.4 percent) can be obtained by measuring the crack mouth displacement and multiplying by 0.773.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 19; July 198
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  • 20
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    On restarts in NASTRAN (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The checkpoint/restart capability available in NASTRAN is very sophisticated. Improvements and enhancements to this capability made with a view to increasing its efficiency and usefulness are considered. Some important features resulting from these changes are discussed. In particular, the different types of restarts available in NASTRAN are described and how they are handled both in the rigid format and DMAP environments explained. The output to restart runs are also illustrated.
    Keywords: STRUCTURAL MECHANICS
    Type: Georgia Univ. 10th NASTRAN User's Colloq.; p 249-267
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  • 21
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    NASTRAN of the HEP (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Preliminary plans for the conversion of NASTRAN to DENELCOR's heterogeneous element processor (HEP) are presented. First, a brief history of computer architecture and the architecture of the HEP computer system are discussed. Second, a description of the HEP computer system is provided. Lastly, the preliminary NASTRAN conversion plans for link management, I/O management, memory management, and code optimization are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: Georgia Univ. 10th NASTRAN User's Colloq.; p 187-203
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  • 22
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    A new capability for elastic aircraft airloads via NASTRAN (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A new direct matrix abstract program for NASTRAN written to calculate internal stresses and airloads for a flexible wing is described. The difficulties encountered in interfacing the doublet lattice solution to the aerodynamic problem to the finite element solution to the structural problem are discussed. A brief numerical example is included.
    Keywords: STRUCTURAL MECHANICS
    Type: Georgia Univ. 10th NASTRAN User's Colloq.; p 165-186
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  • 23
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    Finite element solution of torsion and other 2-D Poisson equations (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The NASTRAN structural analysis computer program may be used, without modification, to solve two dimensional Poisson equations such as arise in the classical Saint Venant torsion problem. The nonhomogeneous term (the right-hand side) in the Poisson equation can be handled conveniently by specifying a gravitational load in a "structural" analysis. The use of an analogy between the equations of elasticity and those of classical mathematical physics is summarized in detail.
    Keywords: STRUCTURAL MECHANICS
    Type: Georgia Univ. 10th NASTRAN User's Colloq.; p 153-164
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  • 24
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    Large displacements and stability analysis of nonlinear propeller structures (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The use of linear rigid formats in COSMIC NASTRAN without DMAP procedures for the analysis of nonlinear propeller structures is described. Approaches for updating geometry and applying follower forces for incremental loading are demonstrated. The COSMIC NASTRAN rigid formats and other independent finite element programs are compared. The comparisons include results from the four approaches for updating the geometry using RIGID FORMAT 1, RIGID FORMATS 4 and 13, MARC and MSC/NASTRAN. It is shown that user friendly updating approaches can be used to predict the large displacements and instability of these nonlinear structures. The approaches are easily implemented by the user and predict conservative results.
    Keywords: STRUCTURAL MECHANICS
    Type: Georgia Univ. 10th NASTRAN User's Colloq.; p 112-132
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  • 25
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    An interactive review system for NASTRAN (1982)
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    Publication Date: 2011-08-18
    Description: An interactive review system that addresses the problems of model display, model error checking, and postprocessing is described. The menu driven system consists of four programs whose advantages and limitations are detailed. The interface between NASTRAN and MOVIE-BYU, the modifications required to make MOVIE usable in a finite element context, and the resulting capabilities of MOVIE as a graphics postprocessor for NASTRAN are illustrated.
    Keywords: STRUCTURAL MECHANICS
    Type: Georgia Univ. 10th NASTRAN User's Colloq.; p 45-64
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  • 26
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    Reliability of the finite element method for calculating free edge stresses in composite laminates (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The interlaminar normal stress distributions along the interface between the +45 deg and -45 deg plies of a graphite/epoxy laminate, obtained by various investigators, were found to disagree in both magnitude and sign. The reliability of the displacement-formulated finite element method in analyzing the edge-stress problem of a composite laminate is investigated. The history of the edge-stress problem is reviewed, and two well-known elasticity problems, one involving a stress discontinuity and one a singularity, are analyzed. The finite element analysis in these problems yields accurate stress distributions everywhere except in two elements closest to the stress discontinuity or singularity. Stress distributions for a + or -45 deg ply laminate near the singularity were similar to those of the two elasticity problems, demonstrating the methods, accuracy for calculating interlaminar stresses in composite laminates. The disagreement between the numerical methods was attributed to the unsymmetric stress tensor at singularity.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 15; 1, 19; 1982
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  • 27
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    Solution of Von Karman's plate equation with perturbation and series summation (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A nonliner series summation technique was combined with Chien's small parameter perturbation technique to solve the problem of the finite deflection of a simply supported circular plate subjected to a uniform transverse load. Problems involving finite deflections of plates with simply supported or free edges were regarded as almost intractable. The great advantage of incorporating the summation method into the solution procedure is demonstrated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Centre Res. in Struct. and Solid Mech., 1982; p 349-361
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  • 28
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    Susceptibility of symmetric structures to nonlinear torsional coupling (1982)
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    Publication Date: 2011-08-18
    Description: The susceptibility to induced torsional response of symmetric building structures with nonliner resisting elements was investigated. Stability curves show the effect of the arrangement of the load resisting elements on induced torsional coupling in these nonliner but other wise symmetric structures. Universal upper and lower bound instability curves are also derived; these identify the susceptibility to torsional coupling of symmetric structures with different stiffness arrangements but which have equal mass and total lateral stiffness, and which are intended to model alternative structural strategies for lateral load resistance.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 313-328
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  • 29
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    Synthesis of frameworks under multilevel performance constraints (1982)
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    Publication Date: 2011-08-18
    Description: A method for the minimum weight design of practical planar frameworks under both service and ultimate loading conditions is presented. Acceptable elastic stresses and displacements are ensured at the service load level while, simultaneously, adequate safety against plastic collapse is ensured at the ultimate load level. The features of the design method for an industrial steel mill building are illustrated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 285-299
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  • 30
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    An exact zooming method for finite element analyses (1982)
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    Publication Date: 2011-08-18
    Description: An exact zooming technique which employs static condensation and exact structural reanalysis methods was developed. Successive application of static condensation reduces the system to one that is only associated with the degrees of freedom (dof) of the original model. Application of an exact static reanalysis technique permits the displacements at the dof of the original model that are contained in the zoomed portion of the structure to be obtained first. The response external to the zoom, as well as the response of additional dof within various levels of zooming, is computed. With the triangular factor of the stiffness matrix of the original system available, this approach involves only the solution of a system of equations of small order.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. Solid Mech., 1982; p 229-249
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  • 31
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    An emulator for minimizing finite element analysis implementation resources (1982)
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    Publication Date: 2011-08-18
    Description: A finite element analysis emulator providing a basis for efficiently establishing an optimum computer implementation strategy when many calculations are involved is described. The SCOPE emulator determines computer resources required as a function of the structural model, structural load-deflection equation characteristics, the storage allocation plan, and computer hardware capabilities. Thereby, it provides data for trading analysis implementation options to arrive at a best strategy. The models contained in SCOPE lead to micro-operation computer counts of each finite element operation as well as overall computer resource cost estimates. Application of SCOPE to the Memphis-Arkansas bridge analysis provides measures of the accuracy of resource assessments. Data indicate that predictions are within 17.3 percent for calculation times and within 3.2 percent for peripheral storage resources for the ELAS code.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 185-199
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  • 32
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    Interaction of heat production, strain rate and stress power in a plastically deforming body under tensile test (1982)
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    Publication Date: 2011-08-18
    Description: At high strain rates the heat produced by plastic deformation can give rise to a rate dependent response even if the material has rate independent constitutive equations. This effect has to be evaluated when interpreting a material test, or else it could erroneously be ascribed to viscosity. A general thermodynamic theory of tensile testing of elastic-plastic materials is given in this paper; it is valid for large strain at finite strain rates. It enables discovery of the parameters governing the thermodynamic strain rate effect, provides a method for proper interpretation of the results of the tests of dynamic plasticity, and suggests a way of planning experiments in order to detect the real contribution of viscosity.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 113-127
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  • 33
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    Nonlinear constitutive theory for turbine engine structural analysis (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A number of viscoplastic constitutive theories and a conventional constitutive theory are evaluated and compared in their ability to predict nonlinear stress-strain behavior in gas turbine engine components at elevated temperatures. Specific application of these theories is directed towards the structural analysis of combustor liners undergoing transient, cyclic, thermomechanical load histories. The combustor liner material considered in this study is Hastelloy X. The material constants for each of the theories (as a function of temperature) are obtained from existing, published experimental data. The viscoplastic theories and a conventional theory are incorporated into a general purpose, nonlinear, finite element computer program. Several numerical examples of combustor liner structural analysis using these theories are given to demonstrate their capabilities. Based on the numerical stress-strain results, the theories are evaluated and compared.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 67-96
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    A semi-implicit dynamic relaxation algorithm for static nonlinear structural analysis (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A semiimplicit dynamic relaxation technique for solution of the nonlinear structural equlibrium equation is presented. A previously presented basic transient response analysis algorithm is employed, permitting use of one solution method and one software module for both static and dynamic analyses. A theoretical comparison of the method with explicit dynamic relaxation techniques shows that it offers a substantially improved convergence property without additional computational overhead.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 1-10
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    the finite element machine: An experiment in parallel processing (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The Finite Element Machine at the NASA Langley Research Center is a prototype computer designed to support parallel solutions to structural analysis problems. The hardware architecture and support software for the machine, initial solution algorithms and test applications, and preliminary results are described. Directions for future work are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: Res. in Struct. and Solid Mech., 1982; p 201-217
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  • 36
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    Integration of multidimensional regions with applications to finite element analysis (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Alternatives to Gaussian integration methods for multidimensional regions are presented. These rules preserve the convergence behavior of the exact integrated element but require fewer evaluation points than the Gauss methods. Numerical examples are given to verify the behavior of the new integration rules.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 171-183
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    A novel boundary element method program for heat transfer analysis of composite materials (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A boundary element method computer program developed for heat transfer analysis of two dimensional composite structures is described. The program runs on a time share mode and interacts with the user for multirun analysis. During a run, the geometry can be modified interactively by the user as many times as desired by using various options available and the new results printed or plotted. A concept of plotting the results for boundary element method is introduced. The advantage of such a program over the finite element method for simple design problems is demonstrated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 141-152
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  • 38
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    Operator split methods in the numerical solution of the finite deformation elastoplastic dynamic problem (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The spatial formulation of the elastoplastic dynamic problem for finite deformations is considered. A thermodynamic argument leads to an additive decomposition of the spatial rate of deformation tensor and allows an operator split of the evolutionary equations of the problem into elastic and plastic parts. This operator split is taken as the basis for the definition of a global product algorithm. In the context of finite element discretization the product algorithm entails, for every time step, the solution of a nonlinear elastodynamic problem followed by the application of plastic algorithms that operate on the stresses and internal variables at the integration points and bring in the plastic constitutive equations. Suitable plastic algorithms are discussed for the cases of perfect and hardening plasticity and viscoplasticity. The proposed formalism does not depend on any notion of smoothness of the yield surface and is applicable to arbitrary convex elastic regions, with or without corners. The stabiity properties of the global product algorithm are shown to be identical to those of the algorithm used for the integration of the nonlinear elastodynamic problem. Numerical examples illustrate the accuracy of the method.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 25-47
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  • 39
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    Dynamic response of lined tunnels by boundary elements (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The dynamic stress concentration manifested around a lined cylindrical tunnel buried in an infinitely extending linear elastic or viscoelastic medium due to the passage of transient disturbances was investigated. Plane strain is assumed to hold and the transient disturbances can be of any arbitrary time variation. The boundary element method formulated in the Laplace transform domain is employed. Isoparametric boundary elements are used in the discretization of the liner and tunnel surfaces. Viscoelastic material behavior can be readily obtained from the linear elastic case in the Laplace transform domain through the use of the correspondence principle. The transient solution is recovered by numerical inversion of the solution obtained in the transformed domain.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 251-264
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  • 40
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    Using NASTRAN to solve symmetric structures with nonsymmetric loads (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A method for computation of reflective dihedral symmetry in symmetrical structures under nonsymmetric loads is described. The method makes it possible to confine the analysis to a half, a quarter, or an octagonal segment. The symmetry of elastic deformation is discussed, and antisymmetrical deformation is distinguished from nonsymmetrical deformation. Modes of deformation considered are axial, bending, membrane, and torsional deformation. Examples of one and two dimensional elements are presented and extended to three dimensional elements. The method of setting up a problem within NASTRAN is discussed. The technique is applied to a thick structure having quarter symmetry which was modeled with polyhedra and subjected to five distinct loads having varying degrees of symmetry.
    Keywords: STRUCTURAL MECHANICS
    Type: 10th NASTRAN User's Colloq.; p 216-232
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  • 41
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    On elastic-plastic analysis of an overloaded breech ring using NASTRAN (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The piece-wise linear analysis option of the NASTRAN code was used to analyze a photoplastic model for a sliding breech mechanism. A two dimensional finite element representation for the breech ring was chosen and the material was made of polycarbonate resin. The aluminum block was regarded as rigid and the width of contact was assumed to remain unchanged during loading. The displacements and stresses in the breech ring were obtained for loading in the elastic as well as plastic range. The maximum tensile stresses before and after complete unloading were obtained and compared with numerical and experimental results.
    Keywords: STRUCTURAL MECHANICS
    Type: Georgia Univ. 10th NASTRAN User's Colloq.; p 143-152
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  • 42
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    Prediction of bead area contact load at the tire-wheel interface using NASTRAN (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The theoretical prediction of the bead area contact load at the tire wheel interface using NASTRAN is reported. The application of the linear code to a basically nonlinear problem results in excessive deformation of the structure and the tire-wheel contact conditions become impossible to achieve. A psuedo-nonlinear approach was adopted in which the moduli of the cord reinforced composite are increased so that the computed key deformations matched that of the experiment. Numerical results presented are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: Georgia Univ. 10th NASTRAN User's Colloq.; p 133-142
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    On the use of harmonic expansions in magnetic field problems in NASTRAN (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The use of a prolate spheroidal harmonic expansion to compute far field results in magnetics problems with the DTNSRDC version of NASTRAN is demonstrated. When field problems with infinite exterior domains are solved by the finite element method, the domain must be modeled to infinity. The density of the finite element mesh usually decreases as the distance from the structure increases, thus degrading the results in the far field.
    Keywords: STRUCTURAL MECHANICS
    Type: Georgia Univ. 10th NASTRAN User's Colloq.; p 65-73
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    Operating in the age of NASTRAN (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The history of the development of the NASTRAN computer program, a general purpose finite element code for structural analysis, is described. The need for research programs to improve analysis of structures, and the writing of a computer program to give numerical solutions for shell behavior, were the impetus for the program design. The use of finite elements to obtain engineering solutions was introduced. The architecture, solution structure, DMAP language, decomposition technique for banded matrices with active columns, general purpose plotter, engineering data inputs, elastic element routines, programmer manuals, of NASTRAN's system design are described.
    Keywords: STRUCTURAL MECHANICS
    Type: 10th NASTRAN User's Colloq.; p 1-11
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  • 45
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    Statics of wrinkling films (1982)
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    Publication Date: 2011-08-18
    Description: An analytical investigation of the equilibrium of wrinkling films is conducted. Zak (1979) has shown that wrinkling occurs in connection with the instability of a smooth film having no resistance to bending in the case of compression. The governing equation for the equilibrium of a film with possible regions of wrinkling is considered. The introduction of fictitious stress reduces the governing equation to a form which formally coincides with the governing equation for a string. Equilibrium conditions in the case of an absence of external forces are explored, taking into account the stretching of a semispherical film, the torsion of a convex film of revolution, and stress singularities. A study is conducted of the equilibrium under conditions in which external forces normal to the surface of a film are present. Attention is also given to the equilibrium in a potential field.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Elasticity; 12; Jan. 198
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  • 46
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    Extensional collapse modes of structural members (1982)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: Attenuation of the load transmitted to a vehicle occupant by the structure, either by modifying structural assembly, changing geometry of its elements, or adding specific load limiting devices to help dissipate kinetic energy was studied. General aviation aircraft have fuselage subfloors of a built up structure which are generally very stiff perpendicular to the floor of the cabin. The subfloor structure, designed to crush at an appropriate force level, can be used to advantage in a crash by dissipating energy through plastic buckling of the floor beams and frames. Simple closed form solutions to predict the mean crushing force levels of subfloor designs is useful in engineering practice. The crushing process of thin walled, plate formed, open structures with particular emphasis on L and cruciform shapes was analyzed. Lower and upper bound solutions for the mean crushing strength of cruciforms are obtained by considering modes of deformation which account for both bending and extensional deformation. It is the importance of extensional deformation to the energy absorption process, representing at least one third of the dissipated energy is shown.
    Keywords: STRUCTURAL MECHANICS
    Type: Res. in Struct. and Solid Mech., 1982; p 405-434
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    Structural fatigue test results for large wind turbine blade sections (1982)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: In order to provide quantitative information on the operating life capabilities of wind turbine rotor blade concepts for root-end load transfer, a series of cantilever beam fatigue tests was conducted. Fatigue tests were conducted on a laminated wood blade with bonded steel studs, a low cost steel spar (utility pole) with a welded flange, a utility pole with additional root-end thickness provided by a swaged collar, fiberglass spars with both bonded and nonbonded fittings, and, finally, an aluminum blade with a bolted steel fitting (Lockheed Mod-0 blade). Photographs, data, and conclusions for each of these tests are presented. In addition, the aluminum blade test results are compared to field failure information; these results provide evidence that the cantilever beam type of fatigue test is a satisfactory method for obtaining qualitative data on blade life expectancy and for identifying structurally underdesigned areas (hot spots).
    Keywords: STRUCTURAL MECHANICS
    Type: Large Horizontal-Axis Wind Turbines; p 303-328
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    Finite element analysis of a deployable space structure (1982)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: To assess the dynamic characteristics of a deployable space truss, a finite element model of the Scientific Applications Space Platform (SASP) truss has been formulated. The model incorporates all additional degrees of freedom associated with the pin-jointed members. Comparison of results with SPAR models of the truss show that the joints of the deployable truss significantly affect the vibrational modes of the structure only if the truss is relatively short.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center The 1982 NASA(ASEE Summer Fac. Fellowship Program; 20 p
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    A formulation of rotor-airframe coupling for design analysis of vibrations of helicopter airframes (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A linear formulation of rotor airframe coupling intended for vibration analysis in airframe structural design is presented. The airframe is represented by a finite element analysis model; the rotor is represented by a general set of linear differential equations with periodic coefficients; and the connections between the rotor and airframe are specified through general linear equations of constraint. Coupling equations are applied to the rotor and airframe equations to produce one set of linear differential equations governing vibrations of the combined rotor airframe system. These equations are solved by the harmonic balance method for the system steady state vibrations. A feature of the solution process is the representation of the airframe in terms of forced responses calculated at the rotor harmonics of interest. A method based on matrix partitioning is worked out for quick recalculations of vibrations in design studies when only relatively few airframe members are varied. All relations are presented in forms suitable for direct computer implementation.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-RP-1089 , L-14243 , NAS 1.61:1089
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    Natural frequency of rotating beams using non-rotating modes (1982)
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    Publication Date: 2019-06-28
    Description: A Lagrangian approach is formulated for predicting the rotating natural frequencies of a beam from the nonrotating modes and frequencies. Using the first two nonrotating mode shapes in one case and the first four such modes in the other case the frequencies of the rotating modes are calculated for a short tapered beam and a typical helicopter blade, respectively. In each case the beam is represented by lumped parameters. The number of mass points representing the beam and the accuracy of the calculated slopes of the nonrotating mode shapes at those points are both shown to affect the accuracy of the resulting frequencies, but the number of stations is shown to be more important.
    Keywords: STRUCTURAL MECHANICS
    Type: American Helicopter Society; vol. 27
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    Influence of deformation behavior, oxydation, and temperature on the long time cyclic stress behavior of high temperature steels (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The influence of different parameters on the creep-fatigue behavior of several steel alloys was investigated. The higher the temperature the lower the crack initiation value. Pauses during the cycle reduce the damage. Oxidation reduces and protective gas increases the lifetime. Prior loading and prior deformation reduce the lifetime. Short annealing slightly affects the cycle stress behavior. The test results do not satisfactorily agree with methods of extrapolation and damage accumulation.
    Keywords: STRUCTURAL MECHANICS
    Type: MPA-82-02 , (ISSN 0721-4529)
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    Stress intensity factors in a hollow cylinder containing a radial crack (1982)
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    Publication Date: 2019-06-28
    Description: In this paper, an exact formulation of the plane elasticity problem for a hollow cylinder or a disk containing a radial crack is given. The crack may be an external edge crack, an internal edge crack, or an embedded crack. It is assumed that on the crack surfaces the shear traction is zero, and the normal traction is an arbitrary function of radius. For various crack geometries and radius ratios, the numerical results are obtained for a uniform crack surface pressure, for a uniform pressure acting on the inside wall of the cylinder, and for a rotating disk.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 20; Dec. 198
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    Mixed time integration methods for transient thermal analysis of structures, appendix 5 (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Mixed time integration methods for transient thermal analysis of structures are studied. An efficient solution procedure for predicting the thermal behavior of aerospace vehicle structures was developed. A 2D finite element computer program incorporating these methodologies is being implemented. The performance of these mixed time finite element algorithms can then be evaluated employing the proposed example problem.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-170061 , NAS 1.26:170061
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    Experimental verification of the Neuber relation at room and elevated temperatures (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The accuracy of the Neuber equation at room temperature and 1,200 F as experimentally determined under cyclic load conditions with hold times. All strains were measured with an interferometric technique at both the local and remote regions of notched specimens. At room temperature, strains were obtained for the initial response at one load level and for cyclically stable conditions at four load levels. Stresses in notched members were simulated by subjecting smooth specimens to he same strains as were recorded on the notched specimen. Local stress-strain response was then predicted with excellent accuracy by subjecting a smooth specimen to limits established by the Neuber equation. Data at 1,200 F were obtained with the same experimental techniques but only in the cyclically stable conditions. The Neuber prediction at this temperature gave relatively accurate results in terms of predicting stress and strain points.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-167967 , NAS 1.26:167967
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    Structural dynamics payload loads estimates (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Methods for the prediction of loads on large space structures are discussed. Existing approaches to the problem of loads calculation are surveyed. A full scale version of an alternate numerical integration technique to solve the response part of a load cycle is presented, and a set of short cut versions of the algorithm developed. The implementation of these techniques using the software package developed is discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-170681 , NAS 1.26:170681 , MCR-82-601
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    Benchmark notch test for life prediction (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The laser Interferometric Strain Displacement Gage (ISDG) was used to measure local strains in notched Inconel 718 test bars subjected to six different load histories at 649 C (1200 F) and including effects of tensile and compressive hold periods. The measurements were compared to simplified Neuber notch analysis predictions of notch root stress and strain. The actual strains incurred at the root of a discontinuity in cyclically loaded test samples subjected to inelastic deformation at high temperature where creep deformations readily occur were determined. The steady state cyclic, stress-strain response at the root of the discontinuity was analyzed. Flat, double notched uniaxially loaded fatigue specimens manufactured from the nickel base, superalloy Inconel 718 were used. The ISDG was used to obtain cycle by cycle recordings of notch root strain during continuous and hold time cycling at 649 C. Comparisons to Neuber and finite element model analyses were made. The results obtained provide a benchmark data set in high technology design where notch fatigue life is the predominant component service life limitation.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165571 , NAS 1.26:165571 , R82AEB358
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    Materials constitutive models for nonlinear analysis of thermally cycled structures (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Effects of inelastic materials models on computed stress-strain solutions for thermally loaded structures were studied by performing nonlinear (elastoplastic creep) and elastic structural analyses on a prismatic, double edge wedge specimen of IN 100 alloy that was subjected to thermal cycling in fluidized beds. Four incremental plasticity creep models (isotropic, kinematic, combined isotropic kinematic, and combined plus transient creep) were exercised for the problem by using the MARC nonlinear, finite element computer program. Maximum total strain ranges computed from the elastic and nonlinear analyses agreed within 5 percent. Mean cyclic stresses, inelastic strain ranges, and inelastic work were significantly affected by the choice of inelastic constitutive model. The computing time per cycle for the nonlinear analyses was more than five times that required for the elastic analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-2055 , E-1125 , NAS 1.60:2055
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    Flightweight radiantly and actively cooled panel: Thermal and structural performance (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A 2- by 4-ft flightweight panel was subjected to thermal/structural tests representative of design flight conditions for a Mach 6.7 transport and to off-design conditions simulating flight maneuvers and cooling system failures. The panel utilized Rene 41 heat shields backed by a thin layer of insulation to radiate away most of the 12 Btu/ft2-sec incident heating. A solution of ethylene glycol in water circulating through tubes in an aluminum-honeycomb-sandwich panel absorbed the remainder of the incident heating (0.8 Btu/sq ft-sec). The panel successfully withstood (1) 46.7 hr of radiant heating which included 53 thermal cycles and 5000 cycles of uniaxial inplane loading of + or - 1200 lfb/in; (2) simulated 2g-maneuver heating conditions and simulated cooling system failures without excessive temperatures on the structural panel; and (3) the extensive thermal/structural tests and the aerothermal tests reported in NASA TP-1595 without significant damage to the structural panel, coolant leaks, or hot-gas ingress to the structural panel.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-2074 , L-15292 , NAS 1.60:2074
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    Self-adaptive predictor-corrector algorithms for static nonlinear structural analysis (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: (Previously announced in STAR as N81-33495)
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 15; 4, 19; 1982
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    On a study of the /Delta T/c and C/asterisk/ integrals for fracture analysis under non-steady creep (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Applications of a vector quantity, path-independent integral which has an energy interpretation to the characterization of crack-tip fields in the range from fast to slow crack propagation are examined. The crack tip characterization parameter is defined in terms of a conservation integral for an area around the crack tip in a two-dimensional cracked body. The actual physical interpretation of the parameter is shown to be the difference in crack lengths displayed by two identical bodies which have equal load histories. A steady-state value is obtained for the parameter for cases of steady-state creep and is shown to be related to the standard path-independent integral for macroscopic self-similar crack growth under mode I conditions. A finite element model is developed for viscoplastic material models, using an initial strain approach with steps in a size employed in tangent stiffness methods.
    Keywords: STRUCTURAL MECHANICS
    Type: Engineering Fracture Mechanics; 16; 5, 19; 1982
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    Molecular dynamics simulation of propagating cracks (1982)
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    Publication Date: 2019-06-28
    Description: Steady state crack propagation is investigated numerically using a model consisting of 236 free atoms in two (010) planes of bcc alpha iron. The continuum region is modeled using the finite element method with 175 nodes and 288 elements. The model shows clear (010) plane fracture to the edge of the discrete region at moderate loads. Analysis of the results obtained indicates that models of this type can provide realistic simulation of steady state crack propagation.
    Keywords: STRUCTURAL MECHANICS
    Type: Scripta Metallurgica; 16; June 198
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  • 62
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    Path-independent integrals in finite elasticity and inelasticity, with body forces, inertia, and arbitrary crack-face conditions (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: (Previously announced in STAR as N81-32547)
    Keywords: STRUCTURAL MECHANICS
    Type: Engineering Fracture Mechanics; 16; 3, 19; 1982
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    Dynamics of bi-periodic structures (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: In order to gain insight into the dynamics of biperiodic aerospace structures, a variety of one- and two-dimensional biperiodic structures are considered. It is shown that bands in which natural frequencies lie for periodic structures are further subdivided as a consequence of the biperiodicity. Analytical solutions for the modes and frequencies of finite-length one-dimensional biperiodic structures are obtained for general boundary conditions. A transmission method is developed to simplify the application of boundary conditions. Some modes are found to occur at frequencies outside the frequency bands predicted for biperiodic structures. Two-dimensional biperiodic crossed beam grillage and truss structures are considered in the present study.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 81; Apr. 8
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    Semi-implicit transient analysis procedures for structural dynamics analysis (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A semi-implicit direct time integration procedure is presented which avoids factorization of the implicit difference solution matrix. The procedure, if properly implemented, requires only vectorial calculations and hence needs the same computer core space as explicit integration procedures. Guidelines for splitting the stiffness matrix into upper and lower matrices are established, which among other things are designed to satisfy a correct transmission of rigid-body motions from element (or grid) to its adjacent elements.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering; 18; Apr. 198
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    Three dimensional finite element analysis of damage accumulation in composite laminate (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A three dimensional finite-element computer program has been developed to analyze layered fiber-reinforced composite laminate. This program is capable of: (1) calculating the detailed stress distribution, (2) identifying the damage zone and mode of failure, (3) analyzing the damage accumulation, and (4) determining the ultimate strength of the composite laminate.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 15; 3, 19; 1982
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    Systematic generation of nonlinear discretized dynamic equilibrium equations of spinning cantilevers (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: General nonlinear discretized governing equations of motion of spinning elastic solids and structures are adjusted for the case of a spinning cantilever with initial geometric imperfections. Consideration is given to second degree nonlinearities in the strain-displacement and velocity-displacement relationships. Parameters of the discretization are developed to include the type and number of the coordinate functions used in the admissible trial solution in order to unify the discretization approaches associated with stationarity principles. The coordinate functions comprise both sets of continuous and piecewise continuous functions employed in the Rayleigh-Ritz and the finite element methods, respectively. Coefficient matrices are provided which contain the energy density expressions and which are adaptable to computer programming.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 15; 3, 19; 1982
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    System identification: A question of uniqueness, revisited (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Questions of uniqueness of parameters which were obtained from a system identification algorithm were investigated. The local properties of the surface defined by the error function were used. Static and dynamic numerical experiments on determinate and indeterminate trusses and on shear buildings illustrate the procedure. Examples are given of loading and sensor configurations which produce unique parameters
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 375-389
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    Constrained multibody system dynamics: An automated approach (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The governing equations for constrained multibody systems are formulated in a manner suitable for their automated, numerical development and solution. The closed loop problem of multibody chain systems is addressed. The governing equations are developed by modifying dynamical equations obtained from Lagrange's form of d'Alembert's principle. The modifications is based upon a solution of the constraint equations obtained through a zero eigenvalues theorem, is a contraction of the dynamical equations. For a system with n-generalized coordinates and m-constraint equations, the coefficients in the constraint equations may be viewed as constraint vectors in n-dimensional space. In this setting the system itself is free to move in the n-m directions which are orthogonal to the constraint vectors.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 363-373
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    Implementation of a C-1 triangular element based on the P-version of the finite element method (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The implementation of a computer code CONE (for C(1) continuity) based on the p-version of the finite element method is described. A hierarchic family of triangular finite elements of degree p 5 is used. This family enforces C(1)-continuity across interelement boundaries, and the code is applicable to fourth order partial differential equations in two independent variables, in particular to the biharmonic equation. Applications to several benchmark problems in plate bending are presented. Sample results are examined and compared with theoretical predictions. In particular the analysis of the bending of a rhombic plate shows a significant improvement over othr published results.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 153-170
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    Minimization versus homotopy algorithms (1982)
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    Publication Date: 2019-06-28
    Description: The relative merits and demerits of the minimization techniques are assessed using globally convergent quasi-Newton algorithms on the one hand and the homotopy algorithms on the other hand for the solution of problems of nonlinear structural analysis. Like the homotopy algorithms, the globally convergent quasi-Newton algorithms are equally suited for the solution of the nonlinear equations of structural analysis directly without having to pose the problem as an equivalent minimization problem. In the close neighborhood of the limit and bifurcation points quasi-Newton algorithms experience difficulties. Homotopy algorithms are robust for practically all types of nonlinear problems but are computationally not as cost effective since they provide an extremely accurate prediction of the response by calculating it as a large number of points. Globally convergent algorithms can perform well with very approximate Hessians, while homotopy algorithms require extremely accurate Hessians. While quasi-Newton algorithms can be very easily structured to exploit sparsity and symmetry, homotopy algorithms are not presently so structured and would require special modifications for exploitation of such features without sacrificing robustness and global convergence.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 11-24
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    Large displacements and stability analysis of nonlinear propeller structures (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The use of linear rigid formats in COSMIC NASTRAN without DMAP procedures for the analysis of nonlinear propeller structures is described. Approaches for updating geometry and applying follower forces for incremental loading are demonstrated. Comparisons are made with COSMIC NASTRAN rigid formats and other independent finite element programs. Specifically, the comparisons include results from the four approaches for updating the geometry using RIGID FORMAT 1, RIGID FORMATS 4 and 13, MARC and MSC/NASTRAN. It is shown that 'user friendly' updating approaches (without DMAPS) can be used to predict the large displacements and instability of these nonlinear structures. These user friendly approaches can be easily implemented by the user and predict conservative results.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-82850 , NAS 1.15:82850
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    The crack problem for a nonhomogeneous plane (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The plane elasticity problem for a nonhomogeneous medium containing a crack is considered. It is assumed that the Poisson's ratio of the medium is constant and the Young's modulus E varies exponentially with the coordinate parallel to the crack. First the half plane problem is formulated and the solution is given for arbitrary tractions along the boundary. Then the integral equation for the crack problem is derived. It is shown that the integral equation having the derivative of the crack surface displacement as the density function has a simple Cauchy type kernel. Hence, its solution and the stresses around the crack tips have the conventional square root singularity. The solution is given for various loading conditions. The results show that the effect of the Poisson's ratio and consequently that of the thickness constraint on the stress intensity factors are rather negligible.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-166001 , NAS 1.26:169276
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    Tensile buckling of advanced turboprops (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Theoretical studies were conducted to determine analytically the tensile buckling of advanced propeller blades (turboprops) in centrifugal fields, as well as the effects of tensile buckling on other types of structural behavior, such as resonant frequencies and flutter. Theoretical studies were also conducted to establish the advantages of using high performance composite turboprops as compared to titanium. Results show that the vibration frequencies are not affected appreciably prior to 80 percent of the tensile speed. Some frequencies approach zero as the tensile buckling speed is approached. Composites provide a substantial advantage over titanium on a buckling speed to weight basis. Vibration modes change as the rotor speed is increased and substantial geometric coupling is present.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-82896 , E-1276 , NAS 1.15:82896
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    Tensile stress-strain behavior of graphite/epoxy laminates (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The tensile stress-strain behavior of a variety of graphite/epoxy laminates was examined. Longitudinal and transverse specimens from eleven different layups were monotonically loaded in tension to failure. Ultimate strength, ultimate strain, and strss-strain curves wee obtained from four replicate tests in each case. Polynominal equations were fitted by the method of least squares to the stress-strain data to determine average curves. Values of Young's modulus and Poisson's ratio, derived from polynomial coefficients, were compared with laminate analysis results. While the polynomials appeared to accurately fit the stress-strain data in most cases, the use of polynomial coefficients to calculate elastic moduli appeared to be of questionable value in cases involving sharp changes in the slope of the stress-strain data or extensive scatter.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-3592 , NAS 1.26:3592
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    The role of peel stresses in cyclic debonding (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: When an adhesively bonded joint is undergoing cyclic loading, one of the possible damage modes that occurs is called cyclic debonding - progressive separation of the adherends by failure of the adhesive bond under cyclic loading. In most practical structures, both peel and shear stresses exist in the adhesive bonding during cyclic loading. The results of an experimental and analytical study to determine the role of peel stresses on cyclic debonding in a mixed mode specimen are presented. Experimentally, this was done by controlling the forces that create the peel stresses by applying a clamping force to oppose the peel stresses. Cracked lap shear joints were chosen for this study. A finite element analysis was developed to assess the effect of the clamping force on the strain energy release rates due to shear and peel stresses. The results imply that the peel stress is the principal stress causing cyclic debonding.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-84504
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    Structures and Dynamics Division research and technology plans, FY 1982 (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Computational devices to improve efficiency for structural calculations are assessed. The potential of large arrays of microprocessors operating in parallel for finite element analysis is defined, and the impact of specialized computer hardware on static, dynamic, thermal analysis in the optimization of structural analysis and design calculations is determined. General aviation aircraft crashworthiness and occupant survivability is also considered. Mechanics technology required for design coefficient, fault tolerant advanced composite aircraft components subject to combined loads, impact, postbuckling effects and local discontinuities are developed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-84509 , NAS 1.15:84509
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    Creep crack-growth: A new path-independent integral (T sub c), and computational studies (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The development of valid creep fracture criteria is considered. Two path-independent integral parameters which show some degree of promise are the C* and (Delta T)sub c integrals. The mathematical aspects of these parameters are reviewed by deriving generalized vector forms of the parameters using conservation laws which are valid for arbitrary, three dimensional, cracked bodies with crack surface tractions (or applied displacements), body forces, inertial effects, and large deformations. Two principal conclusions are that (Delta T)sub c has an energy rate interpretation whereas C* does not. The development and application of fracture criteria often involves the solution of boundary/initial value problems associated with deformation and stresses. The finite element method is used for this purpose. An efficient, small displacement, infinitesimal strain, displacement based finite element model is specialized to two dimensional plane stress and plane strain and to power law creep constitutive relations. A mesh shifting/remeshing procedure is used for simulating crack growth. The model is implemented with the quartz-point node technique and also with specially developed, conforming, crack-tip singularity elements which provide for the r to the n-(1+n) power strain singularity associated with the HRR crack-tip field. Comparisons are made with a variety of analytical solutions and alternate numerical solutions for a number of problems.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-167897 , NAS 1.26:167897
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    Buckling test of a 3-meter-diameter corrugated graphite-epoxy ring-stiffened cylinder (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: A three m diameter by three m long corrugated cylindrical shell with external stiffening rings was tested to failure by buckling. The corrugation geometry for the graphite epoxy composite cylinder wall was optimized to withstand a compressive load producing an ultimate load intensity of 157.6 kN/m without buckling. The test method used to produce the design load intensity was to mount the specimen as a cantilevered cylinder and apply a pure bending moment to the end. A load introduction problem with the specimen was solved by using the BOSOR 4 shell of revolution computer code to analyze the shell and attached loading fixtures. The cylinder test loading achieved was 101 percent of design ultimate, and the resulting mass per unit of shell wall area was 1.96 kg/sq m.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-2032 , L-14659 , NAS 1.60:2032
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    Cryogenic performance of slotted brazed Rene 41 honeycomb panels (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Two brazed Rene 41 honeycomb panels that would incorporate a frame element were designed, fabricated and tested. The panels were representative of the lower surface of an advanced space transportation vehicle. The first panel was a two span panel supported by a center frame and on edges parallel to it. The second panel was a two span panel supported by a center frame and on edges parallel to it. The second panel was a three span panel supported on two frames and on edges parallel to the frames. Each panel had its outer skin slotted to reduce the thermal stresses of the panel skins. The first panel was tested under simulated boost conditions that included liquid hydrogen exposure of the frame and inner skin and radiant heat to 478K on the outer skins. The first panel was tested to investigate the effect of thermal stresses in skins and core caused by the panel being restrained by a cold integral frame and to observe the effects of frost formation and possible liquid air development in and around outer skin slots.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-3525 , NAS 1.26:3525 , D180-26653-1
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    Mechanisms of deformation and fracture in high temperature low cycle fatigue of Rene 80 and IN 100 (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Specimens tested for the AGARD strain range partitioning program were investigated. Rene 80 and IN 100 were tested in air and in vacuum; at 871 C, 925 C, and 1000 C; and in the coated and uncoated condition. The specimens exhibited a multiplicity of high-temperature low-cycle fatigue damage. Observations of the various forms of damage were consistent with material and testing conditions and were generally in agreement with previous studies. In every case observations support a contention that failure occurs at a particular combination of crack length and maximum stress. A failure criterion which is applicable in the regime of testing studied is presented. The predictive capabilities of this criterion are straight forward.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165498 , NAS 1.26:165498
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    Photo-orthotropic elasticity - A new technique for stress analysis of composites (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper deals with the application of photoelastic methods to glass fiber reinforced plastics. The basic principles governing the photoelastic response in birefringent orthotropic composites are briefly reviewed. Then, three important aspects of photo-orthotropic elasticity, namely, photoelastic calibration, separation of principal stresses, and application to problems of engineering importance, are considered in detail. A new calibration specimen is proposed for determining the three independent photoelastic constants: an orthotropic half-plane subjected to a concentrated edge load. From the isochromatic response, the three stress-fringe values can be obtained by a least-squares procedure based on the theoretical stress distribution. Next, four methods of separating the principal stresses in birefringent composite models are proposed: the method of drilling small holes at the points of interest, the method of oblique incidence, the method of combining the transmitted photoelastic response with the reflected photoelastic response, and the method of birefringence dispersion.
    Keywords: STRUCTURAL MECHANICS
    Type: Optical Engineering; 21; July-Aug
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    Crack problems for a rectangular plate and an infinite strip (1982)
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    Publication Date: 2019-06-28
    Keywords: STRUCTURAL MECHANICS
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    Application of the line-spring model to a cylindrical shell containing a circumferential or axial part-through crack (1982)
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    Publication Date: 2019-06-28
    Description: The line-spring model developed by Rice and Levy (1972) is used to obtain an approximate solution for a cylindrical shell containing a part-through surface crack. A Reissner type theory is used to account for the effects of the transverse shear deformations, and the stress intensity factor at the deepest penetration point of the crack is tabulated for bending and membrane loading by varying three-dimensionless length parameters of the problem formed from the shell radius, the shell thickness, the crack length, and the crack depth. The upper bounds of the stress intensity factors are provided, and qualitatively the line-spring model gives the expected results in comparison with elasticity solutions.
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    Advances and trends in plate buckling research (1982)
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    Publication Date: 2019-06-28
    Description: Advances and current trends in plate bucklin research are summarized. The field is divided into three parts: (1) classical buckling studies, including plates of rectangular, circular and other shapes; (2) classical complicating effects, including elastic foundation, anisotropic material, variable thickness, shear deformation and nonhomogeneous material; and (3) nonclassical considerations, including postbuckling, imperfections, parametric excitation, follower forces, magnetoelastic buckling and inelastic buckling.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 329-348
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    A finite element approach for shells of revolution with a local deviation (1982)
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    Publication Date: 2019-06-28
    Description: A finite element model that is suitable for the static analysis of shells of revolution with arbitrary local deviations is presented. The model employs three types of elements: rotational, general, and transitional shell elements. The rotational shell elements are used in the region where the shell is axisymmetric. The general shell element are used in the local region of the deviation. The transitional shell elements connect these two distinctively different types of elements and make it possible to combine them in a single analysis. The form of the global stiffness matrix resulting when different forms of nodal degrees of freedom are combined is illustrated. The coupling of harmonic degrees of freedom due to the locally nonaxisymmetric geometry was studied. The use of a substructuring technique and separate partial harmonic analysis is recommended.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 265-283
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    Prediction of residual tensile strength of transversely impacted composite laminates (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The response to low velocity impact of graphite-epoxy T300/5208 composite laminates is discussed. Steel balls of 3/8 inch, 5/8 inch, and 1 inch diameter were the projectiles. Impact energy was limited to 1.2 joules. Impacted specimens were ultrasonically C scanned to determine the impact damaged region. The threshold value of impact energy for impact damage was found to be approximately 0.3 joules. A model was developed to predict the tensile residual strength of impact damaged specimens from fracture mechanics concepts. Impacted specimens were tested in tension to provide a fracture data base. The experimental results agreed well with the predictions from fracture mechanics. In this study, the maximum impact velocity used to simulate the low velocity transverse impact from common objects like tool drops was 10 m/s.
    Keywords: STRUCTURAL MECHANICS
    Type: Res. in Struct. and Solid Mech., 1982; p 97-111
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    Improved damage tolerance of titanium by adhesive lamination (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Basic damage tolerance properties of Ti-6A1-4V titanium plate can be improved by laminating thin sheets of titanium with adhesives. Compact tension and center cracked tension specimens made from thick plate, thin sheet, and laminated plate (six plies of thin sheet) were tested. The fracture toughness of the laminated plate was 39 percent higher than the monolithic plate. The laminated plate's through the thickness crack growth rate was about 20 percent less than that of the monolithic plate. The damage tolerance life of the surface cracked laminate was 6 to over 15 times the life of a monolithic specimen. A simple method of predicting crack growth in a crack ply of a laminate is presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-84525 , NAS 1.15:84525
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    Measured and calculated effects of angle of attack on the transonic flutter of a supercritical wing (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: For abstract see A82-30143.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-83276 , NAS 1.15:83276
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    A computer package for the design and eigenproblem solution of damped linear multidegree of freedom systems (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Systems described by the matrix differental equation are considered. An interactive design routine is presented for positive definite mass, damping, and stiffness matrices. Designing is accomplished by adjusting the mass, damping, and stiffness matrices to obtain a desired oscillation behavior. The algorithm also features interactively modifying the physical structure of the system, obtaining the matrix structure and a number of other system properties. In case of a general system, where the M, C, and K matrices lack any special properties, a routine for the eigenproblem solution of the system is developed. The latent roots are obtained by computing the characteristic polynomial of the system and solving for its roots. The above routines are prepared in FORTRAN IV and prove to be usable for the machines with low core memory.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 391-403
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    A simulation language approach to structural interaction problems (1982)
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    Publication Date: 2019-06-28
    Description: Advantages and disadvantages of using simulation languages in solving structural problems are given. Structural and solid mechanics problems which have strong interactions with other disciplines are emphasized. An aeroservoelastic illustration is described with significant interactions between the dynamics of a flexible flight vehicle structure, the aerodynamics to which it is subjected, the dynamic flight equations, and the vehicle's servo-control system.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 301-312
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    Results from tests of three prototype general aviation seats (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Three types of energy absorbing general aviation seats were dynamically tested and evaluated for crash load attenuation. On the basis of the static and dynamic test results, it was recommended that the tubular frame seats be redesigned to initiate stroking at approximately 12 G's rather than the 20 to 25 G range. Lower density foam was recommended for the foam wedge passenger seat.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-84533 , NAS 1.15:84533
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    Transient thermal stress problem for a circumferentially cracked hollow cylinder (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The transient thermal stress problem for a hollow elasticity cylinder containing an internal circumferential edge crack is considered. It is assumed that the problem is axisymmetric with regard to the crack geometry and the loading, and that the inertia effects are negligible. The problem is solved for a cylinder which is suddenly cooled from inside. First the transient temperature and stress distributions in an uncracked cylinder are calculated. By using the equal and opposite of this thermal stress as the crack surface traction in the isothermal cylinder the crack problem is then solved and the stress intensity factor is calculated. The numerical results are obtained as a function of the Fourier number tD/b(2) representing the time for various inner-to-outer radius ratios and relative crack depths, where D and b are respectively the coefficient of diffusivity and the outer radius of the cylinder.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165989 , NAS 1.26:169024
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    The elasticity problem for a thick-walled cylinder containing a circumferential crack (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The elasticity problem for a long hollow circular cylinder containing an axisymmetric circumferential crack subjected to general nonaxisymmetric external loads is considered. The problem is formulated in terms of a system of singular integral equations with the Fourier coefficients of the derivative of the crack surface displacement as density functions. The stress intensity factors and the crack opening displacement are calculated for a cylinder under uniform tension, bending by end couples, and self-equilibrating residual stresses.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165988 , NAS 1.26:169025
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    Microstructural effects on the room and elevated temperature low cycle fatigue behavior of Waspaloy (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Longitudinal specimens of Waspaloy containing either coarse grains with small gamma or fine grains with large gamma were tested in air at a frequency of 0.33 Hz or 0.50 Hz. The coarse grained structures exhibited planar slip on (III) planes and precipitate shearing at all temperatures. Cracks initiated by a Stage 1 mechanism and propagated by a striation forming mechanism. At 700 C and 800 C, cleavage and intergranular cracking were observed. Testing at 500 C, 700 C, and 800 C caused precipitation of grain boundary carbides. At 700 C, carbides precipitated on slip bands. The fine grained structures exhibited planar slip on (111) planes. Dislocations looped the large gamma precipitates. This structure led to stress saturation and propagation was observed. Increasing temperatures resulted in increased specimen oxidation for both heat treatments. Slip band and grain boundary oxidation were observed. At 800 C, oxidized grain boundaries were cracked by intersecting slip bands which resulted in intergranular failure. The fine specimens had crack initiation later in the fatigue life, but with more rapid propagation crack propagation.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165497 , NAS 1.26:165497
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  • 95
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    Design detail verification tests for a lightly loaded open-corrugation graphite-epoxy cylinder (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Flat corrugated graphite-epoxy panels were tested in compression to verify selected design details of a ring-stiffened cylinder that was designed to support an axial compressive load of 157.6 kN/m without buckling. Three different sizes of subcomponent panels, with the same basic corrugation geometry, were tested: (1) 60.96-cm-long by 45.72-cm-wide panels to evaluate the local buckling strength of the shell wall design; (2) 91.44-cm-long by 45.72-cm-wide panels to evaluate a longitudinal joint and the load-introduction method; and (3) 254.0-cm-long by 91.44-cm-wide panels with four simulated-ring stiffeners to evaluate the ring-attachment method. The test results indicate that the modified shell-wall design, the longitudinal joint, the load-introduction method, and the stiffener-attachment method for the proposed cylinder have adequate strength to support the design load.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-1981 , L-14795 , NAS 1.60:1981
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  • 96
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    Elastic-plastic finite-element analyses of thermally cycled single-edge wedge specimens (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Elastic-plastic stress-strain analyses were performed for single-edge wedge alloys subjected to thermal cycling in fluidized beds. Three cases (NASA TAZ-8A alloy under one cycling condition and 316 stainless steel alloy under two cycling conditions) were analyzed by using the MARC nonlinear, finite-element computer program. Elastic solutions from MARC showed good agreement with previously reported solutions that used the NASTRAN and ISO3DQ computer programs. The NASA TAZ-8A case exhibited no plastic strains, and the elastic and elastic-plastic analyses gave identical results. Elastic-plastic analyses of the 316 stainless steel alloy showed plastic strain reversal with a shift of the mean stresses in the compressive direction. The maximum equivalent total strain ranges for these cases were 13 to 22 percent greater than that calculated from elastic analyses.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-1982 , E-687 , NAS 1.60:1982
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  • 97
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    Alternative ways for formulation of hybrid stress elements (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: An element stiffness matrix can be derived by the conventional potential energy principle and, indirectly, also by generalized variational principles, such as the Hu-Washizu principle and the Hellinger-Reissner principle. The present investigation has the objective to show an approach which is concerned with the formulation of incompatible elements for solid continuum and for plate bending problems by the Hellinger-Reissner principle. It is found that the resulting scheme is equivalent to that considered by Tong (1982) for the construction of hybrid stress elements. In Tong's scheme the inversion of a large flexibility matrix can be avoided. It is concluded that the introduction of additional internal displacement modes in mixed finite element formulations by the Hellinger-Reissner principle and the Hu-Washizu principle can lead to element stiffness matrices which are equivalent to the assumed stress hybrid method.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering; 18; Nov. 198
    Format: text
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  • 98
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    Moving cracks in layered composites (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A three-layered composite with a crack spreading in the center layer has been analytically examined to evaluate the effect of material nonhomogeneity on a constant velocity crack. Two different loading characteristics are considered. In the first case, crack motion is maintained by uniform tensile stresses. In the other, crack deformation is caused by anti-plane shear stresses. Galilean transformation and Fourier sine and cosine transforms are used to determine dynamic crack tip stress fields. Standard Fredholm integral equations yield the dynamic stress intensity factors. The results show that the intensity of local dynamic stresses increases or decreases with crack length to layer thickness as a function of the relative magnitudes of the adjoining layer's material properties. Crack speed tends to increase the effect of material nonhomogeneity.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Engineering Science; 20; 11, 1; 1982
    Format: text
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  • 99
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    On composites with periodic structure (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The overall moduli of a composite with an isotropic elastic matrix containing periodically distributed (anisotropic) inclusions or voids, can be expressed in terms of several infinite series which only depend on the geometry of the inclusions or voids, and hence can be computed once and for all for given geometries. For solids with periodic structures these infinite series play exactly the same role as does Eshelby's tensor for a single inclusion or void in an unbounded elastic medium. For spherical and circular-cylindrical geometries, the required infinite series are calculated and the results are tabulated. These are then used to estimate the overall elastic moduli when either the overall strains or the overall stresses are prescribed, obtaining the same results. These results are compared with other estimates and with experimental data. It is found that the model of composites with periodic structure yields estimates in excellent agreement with the experimental observations.
    Keywords: STRUCTURAL MECHANICS
    Type: Mechanics of Materials; 1; Sept
    Format: text
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  • 100
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    Study of NSI and related cable performance during tests performed in the NASA Hot Gas Facility (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Some seven different configurations of the NSI and other cables were tested in the NASA-MSFC Hot Gas Facility (HGF). The tests were conducted to study what happens to the cables when they are exposed to hot flow as was the case in the first two Shuttle flights, the STS-1 and STS-2. Protection of these components is vital for various functions especially to attain proper nozzle separation. The tests in the HGF demonstrated the severity of the aerodynamic forces combined with aero heating environment on the test cables and helped, in general, to evaluate the cable wrap materials and cable mounting hardware and technique. Blastape 2 cable wrap which is adequate for thermal protection of the cables must be properly clamped at its ends. The nylon clamps (or ties) used to secure cables to metal components inside the skirt could not withstand the heating. K5NA closeout material used on the outboard surface of the aft skirt when troweled over the cables performed excellently in protecting the cables and mounting hardware.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-170886 , NAS 1.26:170886 , LMSC-HREC-TM-D784644
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