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  • General Chemistry  (9,479)
  • Organic Chemistry  (6,748)
  • Chemical Engineering  (2,961)
  • Cell & Developmental Biology
  • STRUCTURAL MECHANICS
  • 2015-2019  (29)
  • 1970-1974  (12,419)
  • 1960-1964  (10,371)
Collection
Keywords
Publisher
Years
Year
  • 101
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    Static aeroelasticity and the flying wing, revisited (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The roll dynamic behavior of some wing configurations is examined. Analysis shows that the static divergence instability which occurs for symmetrical or clamped sweptforward wings is modified by roll freedom. The instability found in the present highly idealized analysis is still of an aperiodic nature, but at a speed above the conventional divergence speed. The magnitude of this difference is seen to be a function of the ratio of the wing roll mass moment of inertia to the mass moment of inertia of the wing about the roll axis, and this difference may be quite significant.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Aircraft; 11; Nov. 197
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  • 102
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    Eigenproblem solution of damped structural systems (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: This article presents an efficient numerical algorithm and a complete listing of the associated computer program, developed for the eigenproblem solution of discrete damped structures, including spinning ones. The numerically stable procedure is based on a combined Sturm sequence and inverse iteration technique, which fully exploits the banded form of the relevant matrices and proves to be most substantially economical when compared to similar existing softwares. Numerical results are presented for representative structures, solved by the present computer program written in FORTRAN V for the JPL UNIVAC 1108 computer.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering; 8; 4, 19; 1974
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  • 103
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    Analysis of twisting stiffness for a multifiber composite layer (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The twisting stiffness of a rectangular cross section consisting of a single row of solid circular cross-section fibers embedded in a matrix is analyzed. The problem is formulated as a Dirichlet torsion problem of a multielement region and solved by the boundary-point least-squares method. Numerical results for a single-fiber square cross section compare favorably with previous relaxation-method results. New numerical results for three and five-fiber composites suggest that the torsional rigidity of a multifiber composite can be approximated from the torsional rigidities of single and three-fiber models.
    Keywords: STRUCTURAL MECHANICS
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  • 104
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    Sizing of complex structure by the integration of several different optimal design algorithms (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Practical design of large-scale structures can be accomplished with the aid of the digital computer by bringing together in one computer program algorithms of nonlinear mathematical programing and optimality criteria with weight-strength and other so-called engineering methods. Applications of this approach to aviation structures are discussed with a detailed description of how the total problem of structural sizing can be broken down into subproblems for best utilization of each algorithm and for efficient organization of the program into iterative loops. Typical results are examined for a number of examples.
    Keywords: STRUCTURAL MECHANICS
    Type: L-9738 , AGARD Structural Optimization; 19 p
    Format: text
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  • 105
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    On the effect of orthotropy in a cracked cylindrical shell (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A pressurized cylindrical shell containing a longitudinal crack is considered. It is assumed that the material has a special orthotropy - namely, that the shear modulus of the sheet may be evaluated from the measured Young's moduli and the Poisson's ratios and is not an independent material constant. Two examples, one for a mildly orthotropic (titanium) and the other for a strongly orthotropic (graphite) material approximately satisfying the condition of special orthotropy are given. The results show that the stress intensity factors are rather strongly dependent on the degree of orthotropy.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 10; Sept
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  • 106
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    Dynamic analysis of an elastic plate on a thin, elastic foundation (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A review, correction, and extension of Vlasov and Leont'ev's (1966) analysis of beams, plates, and shells on elastic foundations is presented, and an improved theory for the motion of an elastic foundation is developed. The interaction of two or more plates resting on a common foundation is included. A simplified model is derived which appears useful for some applications.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 35; Aug. 8
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  • 107
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    Automated design of aerospace structures (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The current state-of-the-art in structural analysis of aerospace vehicles is characterized, automated design technology is discussed, and an indication is given of the future direction of research in analysis and automated design. Representative computer programs for analysis typical of those in routine use in vehicle design activities are described, and results are shown for some selected analysis problems. Recent and planned advances in analysis capability are indicated. Techniques used to automate the more routine aspects of structural design are discussed, and some recently developed automated design computer programs are described. Finally, discussion is presented of early accomplishments in interdisciplinary automated design systems, and some indication of the future thrust of research in this field is given.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 73-DE-K
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  • 108
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    Fracture and contact problems for an elastic wedge (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The plane elastostatic contact problem for an infinite elastic wedge of arbitrary angle is discussed. The medium is loaded through a frictionless rigid wedge of a given symmetric profile. Using the Mellin transform formulation the mixed boundary value problem is reduced to a singular integral equation with the contact stress as the unknown function. With the application of the results to the fracture of the medium in mind, the main emphasis in the study has been on the investigation of the singular nature of the stress state around the apex of the wedge and on the determination of the contact pressure.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-140582
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  • 109
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    Crack opening stretch in a plate of finite width (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The problem of a uniaxially stressed plate of finite width containing a centrally located damage zone is considered. It is assumed that the flaw may be represented by a part-through crack perpendicular to the plate surface, the net ligaments in the plane of the crack and through-the-thickness narrow strips ahead of the crack ends are fully yielded, and in the yielded sections the material may carry only a constant normal traction with magnitude equal to the yield strength. The problem is solved by neglecting the bending effects and the crack opening stretches at the center and the ends of the crack are obtained. Some applications of the results are indicated by using the concepts of critical crack opening stretch and constant slope plastic instability.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-140583
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  • 110
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    Tradeoffs in manipulator structure and control. Part 1: Summary (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The study of various aspects of manipulator design and control is summarized, focusing on the interaction of the structure's flexible dynamics and the dynamics of the joint control system, including specific information on modeling and design, modal analysis and control, and the flexible manipulator analysis computer program, FMAP.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-120493
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  • 111
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    A method for determining local elastoplastic stress and strain in metallurgically bonded notched laminates subjected to a loading cycle (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A semianalytical method was developed for determining elastoplastic cyclic stresses and strains at notch roots in metallurgically bonded metal laminates. The method is based on the Neuber equation, which was used with an effective stress-strain curve for the laminate. It was applied to laminates containing a circular hole which were subjected to one cycle of reversed loading. The laminates consisted of two elasto-perfectly-plastic materials with different yield strengths and with either equal or different Young's moduli. A laminate of high-strength titanium alloy with alternate layers of commercially pure titanium was also analyzed. The accuracy of the method was evaluated by comparing the stresses and strains with those calculated from a finite-element analysis. The results estimated by the simple method based on the Neuber equation agreed closely with the results computed from the more elaborate finite-element analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7766 , L-9753
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  • 112
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    Tradeoffs in manipulator structure and control. Part 4: Flexible manipulator analysis program (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The Flexible Manipulator Analysis Program (FMAP) is a collection of FORTRAN coding to allow easy analysis of the flexible dynamics of mechanical arms. The user specifies the arm configuration and parameters and any or all of several frequency domain analyses to be performed, while the time domain impulse response is obtained by inverse Fourier transformation of the frequency response. A detailed explanation of how to use FMAP is provided.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-120495
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  • 113
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    An elastoplastic analysis of a uniaxially loaded sheet with an interference-fit bolt (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The stresses and strains in a uniaxially loaded sheet with an unloaded interference-fit bolt were calculated by an elastoplastic finite-element analysis. The material properties represented a 7075-T6 aluminum alloy sheet and a steel bolt. The analysis considered the two ideal cases of no slip and no friction at the bolt-sheet interface for a single combination of bolt diameter, interference level, and cyclic loading. When the bolt was inserted, the sheet deformed plastically near the hole; the first tensile load cycle produced additional yielding, but subsequent cycles to the same level caused only elastic cyclic stresses. These stresses together with fatigue data for unnotched specimens were used to estimate crack initiation periods and initiation sites. The cases analyzed with interference-fit bolts were predicted to have crack initiation periods which were about 50 times that for a clearance-fit bolt. Crack initiation was predicted to occur on the transverse axis at a distance of about one radius from the hole.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7748 , L-9593
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  • 114
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    A shock spectra and impedance method to determine a bound for spacecraft structural loads (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A method to determine a bound of structural loads for a spacecraft mounted on a launch vehicle is developed. The method utilizes the interface shock spectra and the relative impedance of the spacecraft and launch vehicle. The method is developed for single-degree-of-freedom models and then generalized to multidegree-of-freedom models.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-140177 , JPL-TM-33-694
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  • 115
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    Modal analysis and control of flexible manipulator arms (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The possibility of modeling and controlling flexible manipulator arms was examined. A modal approach was used for obtaining the mathematical model and control techniques. The arm model was represented mathematically by a state space description defined in terms of joint angles and mode amplitudes obtained from truncation on the distributed systems, and included the motion of a two link two joint arm. Three basic techniques were used for controlling the system: pole allocation with gains obtained from the rigid system with interjoint feedbacks, Simon-Mitter algorithm for pole allocation, and sensitivity analysis with respect to parameter variations. An improvement in arm bandwidth was obtained. Optimization of some geometric parameters was undertaken to maximize bandwidth for various payload sizes and programmed tasks. The controlled system is examined under constant gains and using the nonlinear model for simulations following a time varying state trajectory.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-120494
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  • 116
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    Mixed mode stress intensity factors for semielliptical surface cracks (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The three-dimensional equations of elasticity are solved for a flat elliptical crack which has nonuniform shear stresses applied to its surfaces. An alternating method is used to determine the mode two and mode three stress intensity factors for a semielliptical surface crack in the surface of a finite thickness solid. These stress intensity factors are presented as a function of position along the crack border for a number of crack shapes and crack depths. This same technique is followed to determine the mode one stress intensity factors for the semielliptical surface crack which has normal loading applied to its surface. Mode one stress intensity factors are presented and compared with the results obtained from previous work.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-134684
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  • 117
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    Some effects of tip fins on wing flutter characteristics (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A wind tunnel investigation has been conducted over the Mach number range from about 0.6 to 1.2 to determine the effects of large tip fins on the flutter characteristics of a swept wing. The basic wing configuration had an aspect ratio of 0.95, leading-edge sweep of 40 deg 0, and trailing-edge sweep of 21 deg. Two of these configurations were modified with tip fins of 60 deg dihedral and had effective aspect ratios of 1.5 and 2.2. In general, the results indicate that the addition of tip fins reduces the flutter speed, with the larger fin having the greater effect. Comparison of the experimental flutter speeds at Mach numbers between 0.60 and 0.90 with calculated values obtained by using doublet-lattice unsteady aerodynamic theory was good. Analytical results where structural and aerodynamic effects of the tip fins were isolated indicated that the reduction in flutter speed produced by the addition of the fins was caused by both effects, with the structural effect being the more pronounced.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7702 , L-9644
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  • 118
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    Development of procedures for calculating stiffness and damping properties of elastomers in engineering applications. Part 2: Elastomer characteristics at constant temperature (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Dynamic properties of a commerical polybutadiene compound were determined at a constant temperature of 32 C by a forced-vibration resonant mass type of apparatus. The constant thermal state of the elastomer was ensured by keeping the ambient temperature constant and by limiting the power dissipation in the specimen. Experiments were performed with both compression and shear specimens at several preloads (nominal strain varying from 0 to 5 percent), and the results are reported in terms of a complex stiffness as a function of frequency. Very weak frequency dependence is observed and a simple power law type of correlation is shown to represent the data well. Variations in the complex stiffness as a function of preload are also found to be small for both compression and shear specimens.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-134704 , MTI-74TR20-PT-2
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  • 119
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    Conical isogrid adapter structural test results. Appendix C: Cylindrical isogrid structures (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Analysis techniques and data for evaluating the load carrying capabilities of cylindrical isogrid structures subjected to compression and body bending loads are presented. Structural tests were conducted on a 120-inch diameter by 37-inch long cylindrical adapter. Photographs and drawings of the flanged isogrid adapter structure are included. The subjects considered are: (1) summary of the test data resulting from structural analysis, (2) techniques for predicting local and general instability, (3) a method for predicting extended local instability, (4) the effects of basic parameter and constant variations in extended local stability analysis, and (5) evaluation of effective skin width and compression buckling of skin panels on the basis of test data.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-120463 , PD-73-0123
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  • 120
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    Buckling of conical shell with local imperfections (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Small geometric imperfections in thin-walled shell structures can cause large reductions in buckling strength. Most imperfections found in structures are neither axisymmetric nor have the shape of buckling modes but rather occur locally. This report presents the results of a study of the effect of local imperfections on the critical buckling load of a specific axially compressed thin-walled conical shell. The buckling calculations were performed by using a two-dimensional shell analysis program referred to as the STAGS (Structural Analysis of General Shells) computer code, which has no axisymmetry restrictions. Results show that the buckling load found from a bifurcation buckling analysis is highly dependent on the circumferential arc length of the imperfection type studied. As the circumferential arc length of the imperfection is increased, a reduction of up to 50 percent of the critical load of the perfect shell can occur. The buckling load of the cone with an axisymmetric imperfections is nearly equal to the buckling load of imperfections which extended 60 deg or more around the circumference, but would give a highly conservative estimate of the buckling load of a shell with an imperfection of a more local nature.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-2991 , L-9331
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  • 121
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    Fracture of composite plates containing periodic buffer strips (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Fracture of a composite plate which consists of perfectly bonded parallel load carrying laminates and buffer strips is considered. Fatigue cracks appear and spread in main laminates or in buffer strips or in both perpendicular to the interfaces. The external load is applied to the plate parallel to the strips and away from the crack region. The problem is solved for fully imbedded cracks and for broken laminates or strips. Corresponding stress intensity factors are calculated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-132641
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  • 122
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    An orthotropic laminate composite containing a layer with a crack (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A laminate composite containing an orthotropic layer with a crack situated normal to the interfaces, and bonded to two orthotropic half-planes of dissimilar materials was considered. The solutions for two different classes of orthotropic materials are presented. In each case, the problem was first reduced to a system of dual integral equations, then to a singular integral equation which was subsequently solved numerically for the stress intensity factors at the tip of the crack. The effect of the material properties on the stress intensity factor was investigated. The generalized plane stress and the plane strain were treated simultaneously.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-132567 , IFSM-74-57 , TR-74-1
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  • 123
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    Vibration and stress analysis of soft-bonded shuttle insulation tiles. Modal analysis with compact widely space stringers (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An efficient iterative procedure is described for the vibration and modal stress analysis of reusable surface insulation (RSI) of multi-tiled space shuttle panels. The method, which is quite general, is rapidly convergent and highly useful for this application. A user-oriented computer program based upon this procedure and titled RESIST (REusable Surface Insulation Stresses) has been prepared for the analysis of compact, widely spaced, stringer-stiffened panels. RESIST, which uses finite element methods, obtains three dimensional tile stresses in the isolator, arrestor (if any) and RSI materials. Two dimensional stresses are obtained in the tile coating and the stringer-stiffened primary structure plate. A special feature of the program is that all the usual detailed finite element grid data is generated internally from a minimum of input data. The program can accommodate tile idealizations with up to 850 nodes (2550 degrees-of-freedom) and primary structure idealizations with a maximum of 10,000 degrees-of-freedom. The primary structure vibration capability is achieved through the development of a new rapid eigenvalue program named ALARM (Automatic LArge Reduction of Matrices to tridiagonal form).
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-132553
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  • 124
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    A note on the effect of bending stiffness of stringers attached to a plate with a crack (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An infinite stringer partially bonded to a plate through a layer of adhesive is considered. The stringer had bending as well as longitudinal stiffness. The effect of the stringer's bending rigidity on the stress intensity factor at the tip of the crack is illustrated. Shear stress distribution between the plate and the stringer and the stress intensity factors are obtained from the solution of a system of Fredholm integral equations. The continuity of displacements along the line of bond is represented by the equations.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-132565 , IFSM-74-55 , TR-74-2
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  • 125
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    Nonlinear equations of motion for the elastic bending and torsion of twisted nonuniform rotor blades (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The equations of motion are developed by two complementary methods, Hamilton's principle and the Newtonian method. The resulting equations are valid to second order for long, straight, slender, homogeneous, isotropic beams undergoing moderate displacements. The ordering scheme is based on the restriction that squares of the bending slopes, the torsion deformation, and the chord/radius and thickness/radius ratios are negligible with respect to unity. All remaining nonlinear terms are retained. The equations are valid for beams with mass centroid axis and area centroid (tension) axis offsets from the elastic axis, nonuniform mass and stiffness section properties, variable pretwist, and a small precone angle. The strain-displacement relations are developed from an exact transformation between the deformed and undeformed coordinate systems. These nonlinear relations form an important contribution to the final equations. Several nonlinear structural and inertial terms in the final equations are identified that can substantially influence the aeroelastic stability and response of hingeless helicopter rotor blades.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7818 , A-5711
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  • 126
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    Shear buckling of square perforated plates (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The behavior of thin square perforated plates under the action of uniform shear deformation is studied experimentally and analytically using finite element analysis. Elastic Shear buckling strength is established as a function of the diameter of a round, centrally located hole in the plate. Post buckling behavior and the behavior of perforated plates with various ring stiffeners are also studied experimentally.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-132548
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  • 127
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    Transient response of multidegree-of-freedom linear systems to forcing functions with inequality constraints (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Optimal control theory is applied to analyze the transient response of discrete linear systems to forcing functions with unknown time dependence but having known bounds. Particular attention is given to forcing functions which include: (1) maximum displacement of any given mass element, (2) maximum relative displacement of any two adjacent masses, and (3) maximum acceleration of a given mass. Linear mechanical systems with an arbitrary number of degrees of freedom and only one forcing function acting are considered. In the general case, the desired forcing function is found to be a function that switches from the upper-to-lower bound and vice-versa at certain moments of time. A general procedure for finding such switching times is set forth.
    Keywords: STRUCTURAL MECHANICS
    Type: Acoustical Society of America; vol. 56
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  • 128
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    Nonlinear panel response by a Monte Carlo approach (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The vibration of clamped and simply supported elastic panels due to subsonic and supersonic turbulent boundary-layer flows is investigated by a Monte Carlo technique. The resulting generalized random forces are simulated numerically from boundary-layer turbulence spectra, and the response analysis is performed in the time domain. The mutual interaction between panel motion and external and/or internal airflow is included. Response studies are performed with respect to rms response, probability structure, peak distribution, threshold crossing and spectral density. The effect on the response statistics of in-plane loading, static pressure differential, and cavity pressure is investigated.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 12; May 1974
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  • 129
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    Grain-grain contact geometry and the propagation of elastic waves in granular media (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: It is shown that the compliance of an orthogonal grain-grain contact is so insensitive to the grain geometry in the contact region that this geometry is not at present an important parameter in theories of the speed of propagation of elastic waves in granular media, such as occur in the earth and in the moon.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Physics; vol. 7
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  • 130
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    Nonlinear analysis of the forced response of structural elements (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A general procedure is presented for the nonlinear analysis of the forced response of structural elements to harmonic excitations. Internal resonances (i.e., modal interactions) are taken into account. All excitations are considered, with special consideration given to resonant excitations. The general procedure is applied to clamped-hinged beams. The results reveal that exciting a higher mode may lead to a larger response in a lower interacting mode, contrary to the results of linear analyses.
    Keywords: STRUCTURAL MECHANICS
    Type: Acoustical Society of America; vol. 55
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  • 131
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    Finite elasto-plastic deformation. I - Theory and numerical examples (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: It is demonstrated that the problem of elasto-plastic finite deformation is governed by a quasi-linear model irrespective of deformation magnitude. This feature follows from the adoption of a rate viewpoint toward finite deformation analysis in an Eulerian reference frame. Objectivity of the formulation is preserved by introduction of a frame-invariant stress rate. Equations for piece-wise linear incremental finite element analysis are developed by application of the Galerkin method to the instantaneously linear governing differential equations of the quasi-linear model. Numerical solution capability has been established for problems of plane strain and plane stress. The accuracy of the numerical analysis is demonstrated by consideration of a number of problems of homogeneous finite deformation admitting comparative analytic solution. It is shown that accurate, objective numerical solutions can be obtained for problems involving dimensional changes of an order of magnitude and rotations of a full radian.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Solids and Structures; 10; Mar. 197
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    A method for detecting structural deterioration in bridges (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: The problem of detecting deterioration in bridge structures is studied with the use of Randomdec analysis. Randomdec signatures, derived from the ambient bridge vibrations in the acoustic range, were obtained for a girder bridge over a period of a year to show the insensitivity of the signatures to environmental changes. A laboratory study was also conducted to show the sensitivity of signatures to fatigue cracks on the order of a centimeter in length in steel beams.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-137548 , NEAR-TR-71
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    Effects of proof loads and combined mode loadings on fracture and flaw growth characteristics of aerospace alloys (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: This experimental program was undertaken to determine the effects of (1) combined tensile and bending loadings, (2) combined tensile and shear loadings, and (3) proof overloads on fracture and flaw growth characteristics of aerospace alloys. Tests were performed on four alloys: 2219-T87 aluminum, 5Al-2.5Sn (ELl) titanium, 6Al-4V beta STA titanium and high strength 4340 steel. Tests were conducted in room air, gaseous nitrogen at -200F (144K), liquid nitrogen and liquid hydrogen. Flat center cracked and surface flawed specimens, cracked tube specimens, circumferentially notched round bar and surface flawed cylindrical specimens were tested. The three-dimensional photoelastic technique of stress freezing and slicing was used to determine stress intensity factors for surface flawed cylindrical specimens subjected to tension or torsion. Results showed that proof load/temperature histories used in the tests have a small beneficial effect or no effect on subsequent fracture strength and flaw growth rates.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-134611 , D180-17997-1
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    Analysis of twist and lean of tall towers (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: A method for analytically determining the amount of twist and lean of a tall tower of equilateral triangular cross section is described. This method is also applicable to tall structures of other shapes and cross-sectional areas. A BASIC computer program that determines the angle of twist and amount of lean is provided.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-70113 , KSC-TR-297-REV-1
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    Users manual: Dynamics of two bodies connected by an elastic tether, six degrees of freedom forebody and five degrees of freedom decelerator (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The equations of motion and a computer program for the dynamics of a six degree of freedom body joined to a five degree of freedom body by a quasilinear elastic tether are presented. The forebody is assumed to be a completely general rigid body with six degrees of freedom; the decelerator is also assumed to be rigid, but with only five degrees of freedom (symmetric about its longitudinal axis). The tether is represented by a spring and dashpot in parallel, where the spring constant is a function of tether elongation. Lagrange's equation is used to derive the equations of motion with the Lagrange multiplier technique used to express the constraint provided by the tether. A computer program is included which provides a time history of the dynamics of both bodies and the tension in the tether.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-120261 , GER-16047
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  • 136
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    Attitude dynamics simulation subroutines for systems of hinge-connected rigid bodies (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: Several computer subroutines are designed to provide the solution to minimum-dimension sets of discrete-coordinate equations of motion for systems consisting of an arbitrary number of hinge-connected rigid bodies assembled in a tree topology. In particular, these routines may be applied to: (1) the case of completely unrestricted hinge rotations, (2) the totally linearized case (all system rotations are small), and (3) the mixed, or partially linearized, case. The use of the programs in each case is demonstrated using a five-body spacecraft and attitude control system configuration. The ability of the subroutines to accommodate prescribed motions of system bodies is also demonstrated. Complete listings and user instructions are included for these routines (written in FORTRAN V) which are intended as multi- and general-purpose tools in the simulation of spacecraft and other complex electromechanical systems.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-138819 , JPL-TR-32-1592
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  • 137
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    Finite element formulations for problems of large elastic-plastic deformation (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: An Eulerian finite element formulation is presented for problems of large elastic-plastic flow. The method is based on Hill's variational principle for incremental deformations, and is suited to isotropically hardening Prandtl-Reuss materials. The formulation is given in a manner which allows any conventional finite element program, for "small strain" elasticplastic analysis, to be simply and rigorously adapted to problems involving arbitrary amounts of deformation and arbitrary levels of stress in comparison to plastic deformation moduli. The method is applied to a necking bifurcation analysis of a bar in plane-strain tension. A unified general formulation of finite element equations, both Lagrangian and Eulerian, for large deformations, with arbitrary choice of the conjugate stress and strain measures, and a discussion is given of other proposed formulations for elastic-plastic finite element analysis at large strain.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-138820
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  • 138
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    On numerically accurate finite element (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: A general criterion for testing a mesh with topologically similar repeat units is given, and the analysis shows that only a few conventional element types and arrangements are, or can be made suitable for computations in the fully plastic range. Further, a new variational principle, which can easily and simply be incorporated into an existing finite element program, is presented. This allows accurate computations to be made even for element designs that would not normally be suitable. Numerical results are given for three plane strain problems, namely pure bending of a beam, a thick-walled tube under pressure, and a deep double edge cracked tensile specimen. The effects of various element designs and of the new variational procedure are illustrated. Elastic-plastic computation at finite strain are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-138821
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  • 139
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    Plastic flow around rigid spherical inclusions (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: The extent of plastic flow in a spherical solid (assumed to be homogeneous and elastically and plastically isotropic), surrounding a concentric rigid sphere was calculated as a function of applied external pressure. The applied pressure necessary to cause plastic deformation throughout the solid was obtained.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-142596 , REPT-2278
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  • 140
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    Substantiation Data for Advanced Beaded and Tubular Structural Panels. Volume 3: Testing (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The test program is described, which was conducted to provide the necessary experimental data to verify the design and analysis methods developed for beaded and tubular panels. Test results are summarized and presented for all local buckling and full size panel tests. Selected representative test data from each of these tests is presented in detail. The results of this program established a valid analysis and design procedure for circular tube panels. Test results from three other configurations show deformational modes which are not adequately accounted for in the present analyses.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-132515
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    The design and use of an error correction information system for NASTRAN (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Error Correction Information System (ECIS) is a system for a two-way transmittal of NASTRAN maintenance information via a data base stored on a nationwide accessible computer. ECIS consists of two data bases. The first data base is used for comments, reporting NASTRAN Software Problem Reports (SPR's) and bookkeeping information which can be updated by the user or the NASTRAN Office. The second data base is used by the NSMO to store all SPR information and updates. The hardware needed by an accessing user is any desktop computer terminal and a telephone to communicate with the central computer. The instruction format is an engineering oriented language and requires less than an hour to obtain a working knowledge of its functions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-72651
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  • 142
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    Design and fabrication of a boron reinforced intertank skirt (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Analytical and experimental studies were performed to evaluate the structural efficiency of a boron reinforced shell, where the medium of reinforcement consists of hollow aluminum extrusions infiltrated with boron epoxy. Studies were completed for the design of a one-half scale minimum weight shell using boron reinforced stringers and boron reinforced rings. Parametric and iterative studies were completed for the design of minimum weight stringers, rings, shells without rings and shells with rings. Computer studies were completed for the final evaluation of a minimum weight shell using highly buckled minimum gage skin. The detail design is described of a practical minimum weight test shell which demonstrates a weight savings of 30% as compared to an all aluminum longitudinal stiffened shell. Sub-element tests were conducted on representative segments of the compression surface at maximum stress and also on segments of the load transfer joint. A 10 foot long, 77 inch diameter shell was fabricated from the design and delivered for further testing.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-132448
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    Graphite-polyimide composite for application to aircraft engines (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: A combined experimental and theoretical investigation was performed in order to (1) demonstrate that high quality angleplied laminates can be made from HT-S/PMR-RI (PMR in situ polymerization of monomeric reactants), (2) characterize the PMR-PI material and to determine the HT-S unidirectional composite properties required for composite micro and macromechanics and laminate analyses, and (3) select HT-S/PMR-PI laminate configurations to meet the general design requirements for high-tip-speed compressor blades. The results of the investigation showed that HT-S/PMR laminate configurations can be fabricated which satisfy the high-tip-speed compressor blade design requirements when operating within the temperature capability of the polymide matrix.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7698 , E-7700
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  • 144
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    User's guide for analysis of finite elastoplastic deformation: The FIPDEF and FIPAX programs for the CDC 6600 (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: Computer programs are presented which provide incremental finite-element analysis capability for problems of quasi-static, finite, elastoplastic deformation in two spatial dimensions (plane strain, plane stress, axisymmetric). Monotonic or cyclic loading of isotropic hardening materials is considered. The only restriction on the form of the stress-strain curve is that the rate of work hardening exceed some small positive value. The user's guide assumes familiarity with both finite-element analysis and FORTRAN IV programming for the CDC 6600. Sufficient information is provided to support problem solving ultization of the programs.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-2998 , E-7610
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  • 145
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    Application of optimality criteria in structural synthesis (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: The rational use of optimality criteria was investigated for a class of structural synthesis problems where materials, configuration and applied load conditions are specified, and the minimum weight design is to be determined. The potential of hybrid methods of structural optimization for dealing with relatively large design problems involving practical complexity was explored. The reduced basis concept in design space was used to decrease the number of generalized design variables dealt with by the mathematical programming algorithm. Optimality criteria methods for obtaining design vectors associated with displacement, system buckling and natural frequency constraints are presented. A stress ratio method was used to generate a basis design vector representing the stress constraints. The finite element displacement method was used as the basic structural analysis tool. Results for several examples of truss systems subject to stress, displacement and minimum size constraints are presented. An assessment of these results indicates the effectiveness of the hybrid method developed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-138612 , UCLA-ENG-7446
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  • 146
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    Transonic flutter study of a 50.5 deg cropped-delta wing with two rearward-mounted nacelles (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Transonic flutter characteristics of three geometrically similar delta-wing models were experimentally determined in the Langley transonic dynamics tunnel at Mach numbers from about 0.6 to 1.2. The models were designed to be simplified versions of an early supersonic transport wing design. The model was an aspect-ratio-1.28 cropped-delta wing with a leadingedge sweep of 50.5 deg. The flutter characteristics obtained for this wing configuration indicated a minimum flutter-speed index near a Mach number of 0.92 and a transonic compressibility dip amounting to about a 27-percent decrease in the flutter-speed index relative to the value at a Mach number of 0.6. Analytical studies were performed for one wing model at Mach numbers of 0.6, 0.7, 0.8, and 0.9 by using both doublet-lattice and lifting-surface (kernel-function) unsteady aerodynamic theory. A comparison of the analytical and experimental flutter results showed good agreement at all Mach numbers investigated.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7544 , L-9348
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  • 147
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    Elastic stability of laminated, flat and curved, long rectangular plates subjected to combined inplane loads (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A method is presented to predict theoretical buckling loads of long, rectangular flat and curved laminated plates with arbitrary orientation of orthotropic axes each lamina. The plate is subjected to combined inplane normal and shear loads. Arbitrary boundary conditions may be stipulated along the longitudinal sides of the plate. In the absence of inplane shear loads and extensional-shear coupling, the analysis is also applicable to finite length plates. Numerical results are presented for curved laminated composite plates with boundary conditions and subjected to various loadings. These results indicate some of the complexities involved in the numerical solution of the analysis for general laminates. The results also show that the reduced bending stiffness approximation when applied to buckling problems could lead to considerable error in some cases and therefore must be used with caution.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-2330 , D6-60227
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  • 148
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    The use of COD and plastic instability in crack propagation and arrest in shells (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The initiation, growth, and possible arrest of fracture in cylindrical shells containing initial defects are dealt with. For those defects which may be approximated by a part-through semi-elliptic surface crack which is sufficiently shallow so that part of the net ligament in the plane of the crack is still elastic, the existing flat plate solution is modified to take into account the shell curvature effect as well as the effect of the thickness and the small scale plastic deformations. The problem of large defects is then considered under the assumptions that the defect may be approximated by a relatively deep meridional part-through surface crack and the net ligament through the shell wall is fully yielded. The results given are based on an 8th order bending theory of shallow shells using a conventional plastic strip model to account for the plastic deformations around the crack border.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-132472 , PAPER-6
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  • 149
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    Three-dimensional crack problems (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: Methods for solving three dimensional crack problems are discussed. The stress intensity factor for the case of uniform pressure on the surface crack is analysis. An analysis of concentrated forces acting on the crack faces parallel to the crack front of a half-plane crack was made. Two dimensional calculations were made using the exact solution for the stress field around an elliptical hole in a uniformly stretched plate. The strain energy density was computed in the neighborhood of the ends of narrow, but sharp, ellipses.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-138652
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    Application of boundary integral method to elastoplastic analysis of V-notched beams (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The boundary integral equation method was applied in the solution of the plane elastoplastic problem. The use of this method was illustrated by obtaining stress and strain distributions for a number of specimens with a single-edge notch and subjected to pure bending. The boundary integral equation method reduced the inhomogeneous biharmonic equation to two coupled Fredholm-type integral equations. These integral equations were replaced by a system of simultaneous algebraic equations and solved numerically in conjunction with a method of successive elastic solutions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7637 , E-7658
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    Differential phase shift keyed communication system (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: A communication system using differential phase-shift-keying (DPSK) transmits and receives binary data without requiring timing or phase reference signals. The system encodes and modulates the data at the transmitter, and decodes and demodulates the data at the receiver, without ambiguity as to the data content.
    Keywords: STRUCTURAL MECHANICS
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    Shear-stress intensity factors for elastic sheets with cover plates (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: Shear stress intensity factors are calculated for three problems concerning inextensible cover plates either bonded to or embedded in an elastic sheet which is under uniaxial tension. The stress intensity factors are small when the ratio of sheet thickness to cover plate length is small and, as the ratio increase, rapidly approach their asymptotic values for infinite sheet thickness. In the problem of the embedded cover plate, the stress intensity factor also depends on the Poisson's ratio of the sheet material. The dependence on Poisson's ratio, however, is significant only when the ratio of sheet thickness to cover plate length is small. Some possible implications of the present results for debonding of reinforced sheets under cyclic loading are briefly discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7473 , L-8882
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  • 153
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    A recurrence matrix method for the analysis of longitudinal and torsional vibrations in non-uniform multibranch beams with variable boundary conditions (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: An approximate method for calculating the longitudinal and torsional natural frequencies and associated modal data of a beamlike, variable cross section multibranch structure is presented. The procedure described is the numerical integration of the first order differential equations that characterize the beam element in longitudinal motion and that satisfy the appropriate boundary conditions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-71973
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    NASTRAN variance analysis and plotting of HBDY elements (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The NASTRAN Thermal Analyzer has been intended to do variance analysis and plot the thermal boundary elements. The objective of the variance analysis addition is to assess the sensitivity of temperature variances resulting from uncertainties inherent in input parameters for heat conduction analysis. The plotting capability provides the ability to check the geometry (location, size and orientation) of the boundary elements of a model in relation to the conduction elements. Variance analysis is the study of uncertainties of the computed results as a function of uncertainties of the input data. To study this problem using NASTRAN, a solution is made for both the expected values of all inputs, plus another solution for each uncertain variable. A variance analysis module subtracts the results to form derivatives, and then can determine the expected deviations of output quantities.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-139007 , EC-245
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  • 155
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    Effect of outdoor exposure at ambient and elevated temperatures on fatigue life of Ti-6Al-4V titanium alloy sheet in the annealed and the solution treated and aged condition (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Specimens of Ti-6Al-4V titanium alloy sheet in the annealed and the solution-treated and aged heat-treatment condition were exposed outdoors at ambient and 560 K (550 F) temperatures to determine the effect of outdoor exposure on fatigue life. Effects of exposure were determined by comparing fatigue lives of exposed specimens to those of unexpected specimens. Two procedures for fatigue testing the exposed specimens were evaluated: (1) fatigue tests conducted outdoors by applying 1200 load cycles per week until failure occurred and (2) conventional fatigue tests (continuous cycling until failure occurred) conducted indoors after outdoor exposure under static load. The exposure period ranged from 9 to 28 months for the outdoor fatigue-test group and was 24 months for the static-load group. All fatigue tests were constant-amplitude bending of specimens containing a drilled hole (stress concentration factor of 1.6). The results of the tests indicate that the fatigue lives of solution-treated and aged specimens were significantly reduced by the outdoor exposure at 560 K but not by the exposure at ambient temperature. Fatigue lives of the annealed specimens were essentially unaffected by the outdoor exposure at either temperature. The two test procedures - outdoor fatigue test and indoor fatigue test after outdoor exposure - led to the same conclusions about exposure effects.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7540 , L-9374
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    Transient Response of Shells of Revolution by Direct Integration and Modal Superposition Methods (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The results of an analytical effort to obtain and evaluate transient response data for a cylindrical and a conical shell by use of two different approaches: direct integration and modal superposition are described. The inclusion of nonlinear terms is more important than the inclusion of secondary linear effects (transverse shear deformation and rotary inertia) although there are thin-shell structures where these secondary effects are important. The advantages of the direct integration approach are that geometric nonlinear and secondary effects are easy to include and high-frequency response may be calculated. In comparison to the modal superposition technique the computer storage requirements are smaller. The advantages of the modal superposition approach are that the solution is independent of the previous time history and that once the modal data are obtained, the response for repeated cases may be efficiently computed. Also, any admissible set of initial conditions can be applied.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-2916 , L-9216
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  • 157
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    Experimental and analytical determination of vibration characteristics of corrugated, flexibly supported, heat-shield panels (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Experimental and analytical natural frequencies, nodal patterns, and typical modal displacements for a corrugated, flexibly supported, heat-shield panel are discussed. Good correlation was found between the experimental data and NASTRAN analytical results for the corrugated panel over a relatively wide frequency spectrum covered in the investigation. Of the two experimental techniques used for mode shape and displacement measurements (a noncontacting displacement sensor system and a holographic technique using a helium-neon, continuous-wave laser), the holographic technique was found, in the present investigation, to be faster and better suited for determining a large number of complex nodal patterns of the corrugated panel.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7562 , L-9364
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  • 158
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    High efficiency multifrequency feed (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: Antenna systems and particularly compact and simple antenna feeds which can transmit and receive simultaneously in at least three frequency bands, each with high efficiency and polarization diversity are described. The feed system is applicable for frequency bands having nominal frequency bands with the ratio 1:4:6. By way of example, satellite communications telemetry bands operate in frequency bands 0.8 - 1.0 GHz, 3.7 - 4.2 GHz and 5.9 - 6.4 GHz. In addition, the antenna system of the invention has monopulse capability for reception with circular or diverse polarization at frequency band 1.
    Keywords: STRUCTURAL MECHANICS
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  • 159
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    Turnstile slot antenna (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: A turnstile slot antenna is disclosed, the antenna being for and integral with a spacecraft having a substantially cylindrical body portion. The antenna comprises a circumferential slot about the periphery of the spacecraft body portion with an annular wave guide cavity defining a radial transmission line disposed within the spacecraft body portion behind and in communication with the circumferential slot. Feed stubs and associated transmission apparatus are provided to excite the annular cavity in quadrature phase such that an omnidirectional, circularly polarized, rotating radiation pattern is generated. The antenna of the instant invention has utility both as a transmitting and receiving device, and ensures continuous telemetry and command coverage with the spacecraft.
    Keywords: STRUCTURAL MECHANICS
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  • 160
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    Rotating raster generator (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: A rotating raster generator is provided which enables display of a television raster at any arbitrary roll angle. The generator includes four integrator circuits each of which receives a first voltage input corresponding to the sine or cosine of the desired roll angle and a second input comprising conventional horizontal or vertical sync pulses. The integrator circuits each comprise an operational amplifier and a capacitor connected for producing a ramp output having a rate of change proportional to the roll angle input, an electronic switch responsive to the sync input for resetting the integrator, and a summer that adds the ramp output of the integrator to the roll angle input so as to provide a zero-centered deflection control voltage.
    Keywords: STRUCTURAL MECHANICS
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  • 161
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    Pulse code modulated signal synchronizer (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A bit synchronizer for a split phase PCM transmission is reported that includes three loop circuits which receive incoming phase coded PCM signals. In the first loop, called a Q-loop, a generated, phase coded, PCM signal is multiplied with the incoming signals, and the frequency and phase of the generated signal are nulled to that of the incoming subcarrier signal. In the second loop, called a B-loop, a circuit multiplies a generated signal with incoming signals to null the phase of the generated signal in a bit phase locked relationship to the incoming signal. In a third loop, called the I-loop, a phase coded PCM signal is multiplied with the incoming signals for decoding the bit information from the PCM signal. A counter means is used for timing of the generated signals and timing of sample intervals for each bit period.
    Keywords: STRUCTURAL MECHANICS
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  • 162
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    Decision feedback loop for tracking a polyphase modulated carrier (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A multiple phase modulated carrier tracking loop for use in a frequency shift keying system is described in which carrier tracking efficiency is improved by making use of the decision signals made on the data phase transmitted in each T-second interval. The decision signal is used to produce a pair of decision-feedback quadrature signals for enhancing the loop's performance in developing a loop phase error signal.
    Keywords: STRUCTURAL MECHANICS
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  • 163
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    Effect of inertia properties on attitude stability of nonrigid spin-stabilized spacecraft (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The phenomenon of energy dissipation in spinning spacecraft is discussed with particular reference to its dependence on spacecraft inertia properties. Specific dissipation mechanisms are identified. The effect of external environmental factors on spin stability is also discussed. Generalized curves are presented relating system stability to the principal inertia ratio for various forms of energy dissipation. Dual-spin systems and the effect of lateral inertia asymmetry are also reviewed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7468 , G-7359
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  • 164
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    Integral flange design program (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An automated interactive flange design program utilizing an electronic desk top calculator is presented. The program calculates the operating and seating stresses for circular flanges of the integral or optional type subjected to internal pressure. The required input information is documented. The program provides an automated procedure for computing stresses in selected flange geometries for comparison to the allowable code values.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-71933
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  • 165
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    An improved exceedance theory for combined random stresses (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: An extension is presented of Rice's classic solution for the exceedances of a constant level by a single random process to its counterpart for an n-dimensional vector process. An interaction boundary, analogous to the constant level considered by Rice for the one-dimensional case, is assumed in the form of a hypersurface. The theory for the numbers of boundary exceedances is developed by using a joint statistical approach which fully accounts for all cross-correlation effects. An exact expression is derived for the n-dimensional exceedance density function, which is valid for an arbitrary interaction boundary. For application to biaxial states of combined random stress, the general theory is reduced to the two-dimensional case. An elliptical stress interaction boundary is assumed and the exact expression for the density function is presented. The equations are expressed in a format which facilitates calculating the exceedances by numerically evaluating a line integral. The behavior of the density function for the two-dimensional case is briefly discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TR-R-418 , L-9120
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  • 166
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    Computer program for supersonic Kernel-function flutter analysis of thin lifting surfaces (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: This report describes a computer program (program D2180) that has been prepared to implement the analysis described in (N71-10866) for calculating the aerodynamic forces on a class of harmonically oscillating planar lifting surfaces in supersonic potential flow. The planforms treated are the delta and modified-delta (arrowhead) planforms with subsonic leading and supersonic trailing edges, and (essentially) pointed tips. The resulting aerodynamic forces are applied in a Galerkin modal flutter analysis. The required input data are the flow and planform parameters including deflection-mode data, modal frequencies, and generalized masses.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-2913 , L-9126
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  • 167
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    Nonlinear analysis of structures (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: The development of nonlinear analysis techniques within the framework of the finite-element method is reported. Although the emphasis is concerned with those nonlinearities associated with material behavior, a general treatment of geometric nonlinearity, alone or in combination with plasticity is included, and applications presented for a class of problems categorized as axisymmetric shells of revolution. The scope of the nonlinear analysis capabilities includes: (1) a membrane stress analysis, (2) bending and membrane stress analysis, (3) analysis of thick and thin axisymmetric bodies of revolution, (4) a general three dimensional analysis, and (5) analysis of laminated composites. Applications of the methods are made to a number of sample structures. Correlation with available analytic or experimental data range from good to excellent.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-2351 , RE-454
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  • 168
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    Analysis and design of advanced composite bounded joints (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Advances in the analysis of adhesive-bonded joints are presented with particular emphasis on advanced composite structures. The joints analyzed are of double-lap, single-lap, scarf, stepped-lap and tapered-lap configurations. Tensile, compressive, and in-plane shear loads are covered. In addition to the usual geometric variables, the theory accounts for the strength increases attributable to adhesive plasticity (in terms of the elastic-plastic adhesive model) and the joint strength reductions imposed by imbalances between the adherends. The solutions are largely closed-form analytical results, employing iterative solutions on a digital computer for the more complicated joint configurations. In assessing the joint efficiency, three potential failure modes are considered. These are adherend failure outside the joint, adhesive failure in shear, and adherend interlaminar tension failure (or adhesive failure in peel). Each mode is governed by a distinct mathematical analysis and each prevails throughout different ranges of geometric sizes and proportions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-2218
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  • 169
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    Automatic frequency control for FM transmitter (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An automatic frequency control circuit for an FM television transmitter is described. The frequency of the transmitter is sampled during what is termed the back porch portion of the horizontal synchronizing pulse which occurs during the retrace interval, the frequency sample compared with the frequency of a reference oscillator, and a correction applied to the frequency of the transmitter during this portion of the retrace interval.
    Keywords: STRUCTURAL MECHANICS
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  • 170
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    Gated compressor, distortionless signal limiter (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: A distortionless gated compressor for limiting the amplitude of a signal so as not to produce undesired signal levels responsive thereto is disclosed. The gated compressor includes a distortionless multiplier which multiplies an AC signal from a factor defined by a DC control signal. The compressor includes a plurality of channels each responsive to a signal produced in response to the multiplier's output. When the signal supplied to any channel exceeds a prescribed level, the level of the DC control signal is reduced to reduce the multiplier's output level and thereby prevent the signal applied to any channel from exceeding its prescribed level.
    Keywords: STRUCTURAL MECHANICS
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  • 171
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    New triangular and quadrilateral plate-bending finite elements (1974)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: A nonconforming plate-bending finite element of triangular shape and associated quadrilateral elements are developed. The transverse displacement is approximated within the element by a quintic polynomial. The formulation takes into account the effects of transverse shear deformation. Results of the static and dynamic analysis of a square plate, with edges simply supported or clamped, are compared with exact solutions. Good accuracy is obtained in all calculations.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7407 , L-9180
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  • 172
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    Thin-metal lined PRD 49-III composite vessels (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Filament wound pressure vessels of various configurations were evaluated for burst strength and fatigue performance. The dimensions and characteristics of the vessels are described. The types of tests conducted are explained. It was determined that all vessels leaked in a relatively few cycles (20 to 60 cycles) with failure occurring in all cases in the metallic liner. The thin liner would de-bond from the composite and buckling took place during depressurization. No composite failures or indications of impeding composite failures were obtained in the metal-lined vessels.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-134555 , ASG-2-5540
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  • 173
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    Cyclic-stress analysis of notches for supersonic transport conditions (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The feasibility of using the finite element method to account for the effects of cyclic load and temperature on local stresses and strains at a notch was demonstrated. The behavior of a notched titanium panel was studied under variable loads and temperatures representative of flight conditions for the lower wing surface of a Supersonic Transport (SST). The analysis was performed with the use of the BOPACE finite-element computer program which provides capability to determine high temperature and large viscoplastic effects caused by cyclic thermal and mechanical loads. The analysis involves the development of the finite-element model as well as determination of the structural behavior of the notched panel. Results are presented for twelve SST flights comprised of five different load-temperature cycles. The results show the approach is feasible, but material response to cyclic loads, temperatures, and hold times requires improved understanding to allow proper modeling of the material.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-132387
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  • 174
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    Stress intensity factors for deep cracks emanating from the corner formed by a hole intersecting a plate surface (1974)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: A technique consisting of a marriage between stress freezing photoelasticity and a numerical method was used to obtain stress intensity factors for natural cracks emanating from the corner at which a hole intersects a plate surface. Geometrics studied were: crack depth to thickness ratios of approximately 0.2, 0.5, and 0.75; crack depth to crack length ratios of approximately 1.0 to 2.0. All final crack geometries were grown under monotonic loading and growth was not self similar with most of the growth occurring through the thickness under remote extension. Stress intensity plate surface K sub s factors were determined at the intersection of the flaw border with the plate surface K sub s and with the edge of the hole K sub h. Results showed that for the relatively shallow flaws K sub h approximately equal to 1.5 K sub s, for the moderately deep flaws K sub h approximately equal to K sub s, and for the deep flaws K sub h approximately equal to 0.5 K sub s, revealing a severe sensitivity of K to flaw geometry.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-136930 , VPI-E-74-1
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  • 175
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    A procedure for verifying the structural integrity of an existing pressurized wind tunnel (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The present work describes the approach employed in verifying the structural integrity at maximum operating pressure of a low turbulence pressurized wind tunnel built in 1939-1940. The approach utilized existing ASME Code guidelines and fracture mechanics techniques in combination with the latest nondestructive examination methods to validate the desired life of the facility while minimizing reconstruction or major modifications. Detailed stress analyses using a finite element computer program and a numerical integration program were performed on critical areas of the tunnel. Critical vessel areas were evaluated for remaining fatigue life. Fracture mechanics analyses of the shell were performed at various regions, and critical flaw sizes at each location were determined. Analysis of the test data permitted the remaining useful life of the tunnel to be estimated at 8 to 10 years.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 74-MAT-12 , Pressure Vessels and Piping Conference; Jun 24, 1974 - Jun 28, 1974; Miami Beach, FL
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  • 176
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    Investigation of pyrotechnic shock (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Review of comparative pyrotechnic shock outputs of various electro-explosive release devices that have been obtained in tests of an instrumented spacecraft structure. This research uses pyrotechnic shock spectra levels as an indicator of shock environment severity in support of a program of pyrotechnic device analysis and redesign intended to reduce shock generation.
    Keywords: STRUCTURAL MECHANICS
    Type: International Instrumentation Symposium; May 21, 1974 - May 23, 1974; Albuquerque, NM
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  • 177
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    Hingeless rotor theory and experiment on vibration reduction by periodic variation of conventional controls (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A preliminary evaluation is made of the concept of vibration reduction by properly selected oscillatory collective and cyclic control applications. The investigations are based on experimental frequency response data covering advance ratios from approximately 0.2 to 0.85. Because there was no instrumentation for the measurement of the pitch and roll vibrations, these values were obtained by properly adding up the flap-bending moments at 3.3 in. Any other quantity representing pitch/roll vibrations can be compensated for in the same fashion. The calculated control inputs required for vibration reduction stay within acceptable limits. For four of the five conditions tested they are smaller than the values used for the frequency response tests. As to be expected, the compensating controls greatly affect the blade loads, i.e., torsion, flap- and chordwise bending.
    Keywords: STRUCTURAL MECHANICS
    Type: Specialists Meeting on Rotorcraft Dynamics; Feb 13, 1974 - Feb 15, 1974; Moffett Field, CA
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  • 178
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    Skylab vibroacoustic test program (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Vibroacoustic testing was performed on the orbital workshop dynamic test article and the payload assembly, the two major elements of the Skylab payload. The testing was conducted on each of the Skylab elements separately in the reverberation chamber at the Johnson Space Center. The two test configurations were high fidelity flight article simulations. The testing was conducted in two phases; in the first phase, acoustic tests were performed at levels simulating the lift-off and atmospheric flight acoustic criteria. In the second phase, low frequency sinusoidal vibration tests were conducted to obtain modal response data. The objectives of the Skylab vibroacoustic test program were to: verify the vibration design and test criteria; qualify selected flight components to the vibroacoustic criteria; and verify analytical models used for dynamic load analyses. This paper describes the vibroacoustic testing and discusses the results.
    Keywords: STRUCTURAL MECHANICS
    Type: AAS PAPER 74-106 , Annual Meeting; Aug 20, 1974 - Aug 22, 1974; Los Angeles, CA
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  • 179
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    Estimation of material properties of a nonlinearly elastic bar (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A method of determining certain characteristic flexural rigidities and elastic properties of nonlinearly elastic materials is presented. An estimation method utilizing perturbation methods and a least squares fitting technique is used to solve the nonlinear differential equation derived from the moment curvature relation, subject to boundary values representing deflections of the bar at discrete points. Deflection data from numerical simulations of a nonlinearly elastic, prismatic bar are used to demonstrate the estimation method. Numerical experiments relating the accuracy of the identification to the number and accuracy of the boundary values are presented. Conclusions based on the numerical experiments are included.
    Keywords: STRUCTURAL MECHANICS
    Type: Southeastern Conference on Theoretical and Applied Mechanics; Mar 21, 1974 - Mar 22, 1974; Washington, DC
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  • 180
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    Viscoelastic structures (1974)
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    Publication Date: 2019-07-13
    Description: Numerical analysis of viscoelastic problems may be achieved by either a step-by-step solution procedure or by the integral transform approach. However, for complicated loading and material property relationships, the latter method proves ineffective. Programs specifically developed for the analysis of viscoelastic structures are considered along with multipurpose programs with specific viscoelastic analysis capabilities.
    Keywords: STRUCTURAL MECHANICS
    Type: Symposium on Structural mechanics computer programs: Surveys, assessments, and availability; Jun 12, 1974 - Jun 14, 1974; College Park, MD
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  • 181
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    High-tip-speed fiber composite compressor blades - Vibration and strength analyses (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: An analytical procedure is described which couples composite mechanics computer codes with NASTRAN. This procedure was used to perform a detailed analysis of a high-tip-speed fiber composite compressor fan blade. The results indicate that the various vibration modes of this blade are highly coupled. Mechanical load ply stresses are well below the corresponding room temperature strengths. Lamination residual stresses are likely to cause transply cracks and interply delamination. Transply cracks and relaxation of root fixity decrease the vibrational frequencies whereas centrifugal stiffening increases them. Comparisons of results for various parameters are presented in tabular and graphical form.
    Keywords: STRUCTURAL MECHANICS
    Type: Conference on Fibrous Composites in Flight Vehicle Design; May 22, 1974 - May 24, 1974; Dayton, OH
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  • 182
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    Combined bending-torsion fatigue reliability of AISI 4340 steel shafting with K sub t = 2.34 (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Results generated by three, unique fatigue reliability research machines which can apply reversed bending loads combined with steady torque are presented. Six-inch long, AISI 4340 steel, grooved specimens with a stress concentration factor of 2.34 and R sub C 35/40 hardness were subjected to various combinations of these loads and cycled to failure. The generated cycles-to-failure and stress-to-failure data are statistically analyzed to develop distributional S-N and Goodman diagrams. Various failure theories are investigated to determine which one represents the data best. The effect of the groove and of the various combined bending-torsion loads on the S-N and Goodman diagrams are determined. Three design applications are presented. The third one illustrates the weight savings that may be achieved by designing for reliability.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 74-WA/DE-12 , American Society of Mechanical Engineers, Winter Annual Meeting; Nov 17, 1974 - Nov 22, 1974; New York, NY
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  • 183
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    Stress analysis of the compact specimen including the effects of pin loading (1974)
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    Publication Date: 2019-07-13
    Description: An improved method of boundary collocation was applied to the two-dimensional stress analysis of the compact specimen. The effects of the pin-loaded holes on stress-intensity factors and crack-opening displacements were investigated for various crack-length-to-specimen-width ratios, hole locations, and internal loadings. The stress-intensity factors for the 'standard' compact specimen under plane-stress or plane-strain conditions were found to be within 1 percent of the stress-intensity factors reported in the ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials (E 399-72) over a range of crack-length-to-specimen-width ratios of 0.4 to 0.7. However, for crack-length-to-specimen-width ratios less than 0.4, the pin-load holes (which were not previously accounted for) had a significant effect on stress intensity and crack-opening displacements.
    Keywords: STRUCTURAL MECHANICS
    Type: Fracture Analysis; National Symposium on Fracture Mechanics; Aug 27, 1973 - Aug 29, 1973; College Park, MD
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  • 184
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    Theory to test comparisons for selected aerospace multishell structures and their interfaces under thermomechanical loadings (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Guidelines for structural shell analyses were obtained on the basis of theory-to-test comparisons made on two large-scale aerospace structures subject to thermomechanical loads. The first structural test was the cylindrical aluminum skin-stringer-ring construction of the S-IC forward skirt and S-II interstage. The second structural test included the truncated, cone-shaped, bonded honeycomb sandwich shell of the Spacecraft Lunar Module Adapter; the cylindrical bonded aluminum honeycomb sandwich construction of the Instrument Unit; and the skin-stringer construction with rings and intercostals of the S-IVB forward skirt. Analyses were made for loadings simulating the flight environment. Elementary shear lag theory was superimposed on shell analysis for interface junctions between stages to obtain favorable theory-to-test stress comparisons.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA PAPER 74-1270 , Canadian Aeronautics and Space Institute and American Institute of Aeronautics and Astronautics, Joint Meeting, Toronto; Oct 30, 1974 - Oct 31, 1974; Toronto; Canada
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  • 185
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    Automated structural design with aeroelastic constraints - A review and assessment of the state of the art (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A review and assessment of the state of the art in automated aeroelastic design is presented. Most of the aeroelastic design studies appearing in the literature deal with flutter, and, therefore, this paper also concentrates on flutter. The flutter design problem is divided into three cases: as isolated flutter mode, neighboring flutter modes, and a hump mode which can rise and cause a sudden, discontinuous change in the flutter velocity. Synthesis procedures are presented in terms of techniques that are appropriate for problems of various levels of difficulty. Current trends, which should result in more efficient, powerful and versatile design codes, are discussed. Approximate analysis procedures and the need for simultaneous consideration of multiple design requirements are emphasized.
    Keywords: STRUCTURAL MECHANICS
    Type: Structural Optimization Symposium; Nov 17, 1974 - Nov 21, 1974; New York, NY
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  • 186
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    Fracture Testing with Surface Crack Specimens (1974)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Recommendations are given for the design, preparation, and static fracture testing of surface crack specimens. The recommendations are preceded by background information including discussions of stress intensity factors, crack opening displacements, and fracture toughness values associated with surface crack specimens. Cyclic load and sustained load tests are discussed briefly.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-71772 , E-8274 , Natl. Symp. on Fracture Mech.; Aug 25, 1975 - Aug 27, 1975; Pittsburgh, PA; united States
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  • 187
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    A review of surface-crack fracture testing (1974)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: A brief historical review of surface-crack testing and analysis is given together with some examples of service failures due to surface cracks. The factors which complicate the analysis and interpretation of surface-crack fracture data are discussed. Current efforts to develop consensus recommendations for tensile testing of surface-crack specimens are summarized.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-71629 , E-8163 , Mater. Eng. Ann. Meeting of the Am. Soc. for Metals; Oct 21, 1974 - Oct 24, 1974; Detroit, MI; United States
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  • 188
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    Nonlinear finite-element analysis of laminated composite shells (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Two aspects of the geometrically nonlinear analysis of laminated composite shells are considered in this paper. The first pertains to the simplifications and computational advantages resulting from the use of group-theoretic methods in conjunction with computerized symbolic (algebraic) manipulation in the element development. The second aspect pertains to the combined effects of shear deformation and nonlinearity on the accuracy and convergence of two-dimensional, shear-flexible stiffness finite element models.
    Keywords: STRUCTURAL MECHANICS
    Type: Computational methods in nonlinear mechanics; International Conference; Sep 23, 1974 - Sep 25, 1974; Austin, TX
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  • 189
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    A review of surface-crack fracture testing (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A brief historical review of surface-crack testing and analysis is given together with some examples of service failures due to surface cracks. The factors which complicate the analysis and interpretation of surface-crack fracture data are discussed. Current efforts to develop consensus recommendations for tensile testing of surface-crack specimens are summarized.
    Keywords: STRUCTURAL MECHANICS
    Type: American Society for Metals, Materials Engineering Annual Meeting; Oct 21, 1974 - Oct 24, 1974; Detroit, MI
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  • 190
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    Contact problem for an elastic reinforcement bonded to an elastic plate (1974)
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    Publication Date: 2019-07-13
    Description: The contact problem for a thin elastic reinforcement bonded to an elastic plate is considered. The stiffening layer is treated as an elastic membrane and the base plate is assumed to be an elastic continuum. The bonding between the two materials is assumed to be either one of direct adhesion or through a thin adhesive layer which is treated as a shear spring. The solution for the simple case in which both the stiffener and the base plate are treated as membranes is also given. The contact stress is obtained for a series of numerical examples. In the direct adhesion case the contact stress becomes infinite at the stiffener ends with a typical square root singularity for the continuum model and behaving as a delta function for the membrane model. In the case of bonding through an adhesive layer the contact stress becomes finite and continuous along the entire contact area.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 74-WA/APM-20 , American Society of Mechanical Engineers, Winter Annual Meeting; Nov 17, 1974 - Nov 22, 1974; New York, NY
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  • 191
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    The problem of edge cracks in an infinite strip (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The elastostatic plane problem of an infinite strip containing two symmetrically located internal cracks perpendicular to the boundary is formulated in terms of a singular integral equation with the derivative of the crack surface displacement as the density function. The solution of the problem is obtained for various crack geometries and for uniaxial tension applied to the strip away from the crack region. The limiting case of the edge cracks is then considered in some detail. The fundamental function of the integral equation is obtained and a numerical technique for solving the singular integral equations with this particular type of fundamental function which is characteristic of the edge cracks is described. The stress-intensity factor for the complete range of net ligament-to-width ratio is calculated. The results also include the solution of the edge crack problem in an elastic half plane.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 74-WA/APM-12 , American Society of Mechanical Engineers, Winter Annual Meeting; Nov 17, 1974 - Nov 22, 1974; New York, NY
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  • 192
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    Utilization survey of prototype structural test article (1974)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A survey was conducted of six aerospace companies and two NASA agencies to determine how prototype structural test articles are used in flight operations. The prototype structures are airframes and similar devices which are used for testing and generally are not flown. The survey indicated the following: (1) prototype test articles are not being discarded after development testing is complete, but are used for other purposes, (2) only two cases of prototypes being refurbished and flown were identified, (3) protective devices and inspection techniques are available to prevent or minimize test article damage, (4) substitute programs from design verification are availabel in lieu of using prototype structural articles, and (5) there is a trend away from dedicated test articles. Four options based on these study results were identified to reduce test and hardware costs without compromising reliability of the flight program.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-120543 , D180-18424-1
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  • 193
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    A method to determine the stored energy function of compressible rubberlike materials (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Keywords: STRUCTURAL MECHANICS
    Type: Mechanical behavior of materials; Symposium; Aug 21, 1974 - Aug 24, 1974; Kyoto; Japan
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  • 194
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    Finite-element analysis of vibration and flutter of cantilever anisotropic plates (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The hybrid stress finite element method is used to study the effects of filament angle and orthotropicity parameter on the vibration and flutter characteristics of cantilevered anisotropic plates. The results indicate a generally strong lack of monotonic dependence on filament angle. Also, the natural frequency in certain cases involving the first few modes, can become relatively insensitive to both filament angle and orthotropicity parameter for a range of filament angle beyond 70 deg. Values of critical dynamic pressure are obtained by a modal approach, in which the mode shapes are obtained by the hybrid stress method. Convergence of the modal method is rather rapid for the configurations analyzed, and a comparison of the method with an exact solution for the case of an isotropic simply supported plate shows that use of six modes gives excellent agreement.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 74-WA/APM-15 , American Society of Mechanical Engineers, Winter Annual Meeting; Nov 17, 1974 - Nov 22, 1974; New York, NY
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  • 195
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    Small-scale yielding analysis of mixed mode plane-strain crack problems (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The small-scale yielding analysis of an elastic-plastic body with a line crack under plane-strain conditions subject to combinations of Mode I and II loadings is examined. The analysis of the near-tip field follows the works of Hutchinson and Rice and Rosengren. Dominant singularity solutions governing the asymptotic behavior of the stresses and strains at the crack tip are obtained for the complete range of loadings between Mode I and II. The results of an accurate finite element technique, which imbeds the dominant singularity solutions, directly relates the near-tip behavior to the elastic stress intensity factors K(I) and K(II). Implications of this study to mixed mode fracture mechanics is also discussed, particularly with respect to the direction of crack initiation and the relation of fracture toughness under mixed modes to that in Mode I. Details of the mixed mode plastic zone sizes and shapes are also given.
    Keywords: STRUCTURAL MECHANICS
    Type: Fracture Analysis; National Symposium on Fracture Mechanics; Aug 27, 1973 - Aug 29, 1973; College Park, MD
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  • 196
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    Some approximation concepts for structural synthesis (1974)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An efficient automated minimum weight design procedure is presented which is applicable to sizing structural systems that can be idealized by truss, shear panel, and constant strain triangles. Static stress and displacement constraints under alternative loading conditions are considered. The optimization algorithm is an adaptation of the method of inscribed hyperspheres and high efficiency is achieved by using several approximation concepts including temporary deletion of noncritical constraints, design variable linking, and Taylor series expansions for response variables in terms of design variables. Optimum designs for several planar and space truss examples problems are presented. The results reported support the contention that the innovative use of approximation concepts in structural synthesis can produce significant improvements in efficiency.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-140937 , PAPER-73-341 , AIAA/ASME/SAE 14th Struct.; Mar 20, 1973 - Mar 22, 1973; Williamsburg, VA; United States|AGARD Structural Optimization; 8 p
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  • 197
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    The prediction of structural response to buffet flow: A state-of-the-art review (1974)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Certain aspects of the dynamic system being discussed are reviewed and important structural and aerodynamic quantities of the system are discussed. A theoretical model is presented which relates these quantities to each other. These quantities are then each, in turn, considered in terms of the state of the art of determining the quantities and in terms of areas where further research is needed. The similarity laws and scaling relationships applicable to determining buffet structural response are then discussed, and areas where simplification is required or may be permissible are mentioned. Finally, the various types of model tests pertinent to predicting response of the aircraft structure to buffet flow are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-72627 , L-9820 , 39th AGARD Structural and Mater. Meeting,; Oct 07, 1974 - Oct 12, 1974; Munich
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  • 198
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    Analysis of edge impact stresses in composite plates (1974)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The in-plane edge impact of composite plates, with or without a protection strip, is investigated. A computational analysis based on the Fast Fourier Transform technique is presented. The particular application of the present method is in the understanding of the foreign object damage problem of composite fan blades. The method is completely general and may be applied to the study of other stress wave propagation problems in a half space. Results indicate that for the protective strip to be effective in reducing impact stresses in the composite the thickness must be equal or greater than the impact contact dimension. Large interface shear stresses at the strip - composite boundary can be induced under impact.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-134720 , AMS-1141
    Format: application/pdf
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  • 199
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    Synthesis of stiffened shells of revolution (1974)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Computer programs for the synthesis of shells of various configurations were developed. The conditions considered are: (1) uniform shells (mainly cones) using a membrane buckling analysis, (2) completely uniform shells (cones, spheres, toroidal segments) using linear bending prebuckling analysis, and (3) revision of second design process to reduce the number of design variables to about 30 by considering piecewise uniform designs. A perturbation formula was derived and this allows exact derivatives of the general buckling load to be computed with little additional computer time.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-138839
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  • 200
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    The circumferentially notched cylindrical bar as a fracture toughness test specimen (1974)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A brief review is given of the application of the notched cylinder as a screening specimen for use in sorting materials in respect to their relative levels of plane strain fracture toughness and a discussion of fracture mechanics applications including Irwin's important contributions in this area. In addition, practical problems encountered in application of this specimen will be presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-71551 , E-7933 , Symp. on Linear Fracture Mech.; Jul 29, 1974 - Jul 30, 1974; Bethlehem, PA; United States
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