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  • Analytical Chemistry and Spectroscopy  (35)
  • STRUCTURAL MECHANICS  (19)
  • 1980-1984  (54)
  • 1
    Electronic Resource
    Electronic Resource
    Isotope dilution mass spectrometry of cholesterol in serum (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 8 (1981), S. 5-9 
    Details
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Isotope dilution mass spectrometry is one of the best candidates for reference and definitive methods for the quantitative measurement of organic compounds. In this study sources of error were investigated. Where possible they were removed, and commercially available equipment had to be modified. The method was applied to the measurement of serum cholesterol. The precision is optimized and in the order of 0.5%. The mean of the recoveries of three measurements is 99.8%. The accuracy of the mean of three measurements is 0.2% if no interference are present in the gas chromatographic mass spectrometric measurements.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200080103
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    Paper (German National Licenses)
    Fulltext
  • 2
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    Recent developments in the design, testing and impact-damage tolerance of stiffened composite panels (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The structural technology of laminated filamentary-composite stiffened-panel structures under combined in-plane and lateral loadings is discussed. Emphasis is on analyzing the behavior of the structures under load, determining appropriate structural proportions for weight efficient configurations, and effects of impact damage and geometric imperfections on structural performance. Experimental data on buckling of panels under in-plane compression validate the analysis and sizing methods, and illustrate structural performance and efficiency obtained from representative structures. It is shown that the strength of panels under in-plane compression can be degraded by low-velocity impact damage, and data are presented which indicate that the matrix is a significant factor influencing tolerance to impact damage.
    Keywords: STRUCTURAL MECHANICS
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Reliability of the finite element method for calculating free edge stresses in composite laminates (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The interlaminar normal stress distributions along the interface between the +45 deg and -45 deg plies of a graphite/epoxy laminate, obtained by various investigators, were found to disagree in both magnitude and sign. The reliability of the displacement-formulated finite element method in analyzing the edge-stress problem of a composite laminate is investigated. The history of the edge-stress problem is reviewed, and two well-known elasticity problems, one involving a stress discontinuity and one a singularity, are analyzed. The finite element analysis in these problems yields accurate stress distributions everywhere except in two elements closest to the stress discontinuity or singularity. Stress distributions for a + or -45 deg ply laminate near the singularity were similar to those of the two elasticity problems, demonstrating the methods, accuracy for calculating interlaminar stresses in composite laminates. The disagreement between the numerical methods was attributed to the unsymmetric stress tensor at singularity.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 15; 1, 19; 1982
    Format: text
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  • 4
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    Cannon launched electromechanical control actuation system development (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The evolution of an electromechanical control actuation system from trade study results through breadboard test and high-g launch demonstration tests is summarized. Primary emphasis is on design, development, integration and test of the gear reduction system.
    Keywords: STRUCTURAL MECHANICS
    Type: JPL The 17th Aerospace Mech. Symp.; p 181-198
    Format: application/pdf
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  • 5
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    Opening of an interface flaw in a layered elastic half-plane under compressive loading (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A static analysis is given of the problem of an elastic layer perfectly bonded, except for a frictionless interface crack, to a dissimilar elastic half-plane. The free surface of the layer is loaded by a finite pressure distribution directly over the crack. The problem is formulated using the two dimensional linear elasticity equations. Using Fourier transforms, the governing equations are converted to a pair of coupled singular integral equations. The integral equations are reduced to a set of simultaneous algebraic equations by expanding the unknown functions in a series of Jacobi polynomials and then evaluating the singular Cauchy-type integrals. The resulting equations are found to be ill-conditioned and, consequently, are solved in the least-squares sense. Results from the analysis show that, under a normal pressure distribution on the free surface of the layer and depending on the combination of geometric and material parameters, the ends of the crack can open. The resulting stresses at the crack-tips are singular, implying that crack growth is possible. The extent of the opening and the crack-top stress intensity factors depend on the width of the pressure distribution zone, the layer thickness, and the relative material properties of the layer and half-plane.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-86282 , NAS 1.15:86282
    Format: application/pdf
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  • 6
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    A new look at numerical analyses of free-edge stresses in composite laminates (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The edge stress problem for a + or - 45 deg graphite/epoxy laminate was examined. The reliability of the displacement formulated finite element method in analyzing the edge stress problem was investigated. Analyses of two well known elasticity problems, one involving a stress discontinuity and one a singularity, showed that the finite element analysis yields accurate stress distributions everywhere except in two elements closest to the stress discontinuity of singularity. Stress distributions for a + or - 45 deg laminate showed the same behavior near the singularity found in the well known problems with exact solutions. The displacement formulated finite element method appears to be a highly accurate technique for calculating interlaminar stress in composite laminates. The disagreement among the numerical methods was attributed to the unsymmetric stress tensor at the singularity.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-1751 , L-13777
    Format: application/pdf
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  • 7
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    Stresses in a three-dimensional unidirectional composite containing broken fibers (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: An approximate solution is developed for the determination of the interlaminar normal and shear stresses in the vicinity of a crack in a three dimensional composite containing unidirectional linearly elastic fibers in an infinite linearly elastic matrix. In order to reduce the complexity of the formulation, certain assumptions are made as to the physically significant stresses to be retained. These simplifications reduce the partial differential equations of elasticity to differential-difference equations which are tractable using Fourier transform techniques. This 'material modeling' approach is in contrast with solutions developed by considering each lamina as a homogeneous, orthotropic layer. The resulting solution does not contain the classical singular stress field for the fibers and the influence of broken fibers on unbroken fibers is felt by a change in stress concentration factors. The matrix stresses however, are unbounded as the fiber spacing vanishes and an equivalent fiber-matrix geometry is proposed which gives the correct singular behavior. The numerical solution is considered in detail and several specific examples are presented. The potential for damaged or debonded zones to be generated by an embedded crack is discussed, and stress concentration factors for fibers near the crack are given. Detailed comparisons are made between the present solution, the analogous two-dimensional problem, and corresponding shear-lag models.
    Keywords: STRUCTURAL MECHANICS
    Type: Engineering Fracture Mechanics; 13; 2, 19; 1980
    Format: text
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  • 8
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    Analysis of a unidirectional composite containing broken fibers and matrix damage (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: An analytical solution is developed for the determination of the stresses and displacements in a unidirectional fiber-reinforced composite containing an arbitrary number of broken fibers as well as longitudinal yielding and splitting of the matrix. The solution is developed using a 'materials-modeling' approach which is based on a shear-lag stress transfer mechanism. The equilibrium equation in the axial direction gives a pair of integral equations which are solved numerically. Excellent agreement is shown to exist between the solution and experimental results for notched unidirectional boron/aluminum laminates without splitting. For brittle matrix composites (i.e., epoxy) equally good results are indicated for both matrix yielding and splitting. For yielding without splitting the fracture strength is found to depend on crack length while for large splitting it is crack length independent.
    Keywords: STRUCTURAL MECHANICS
    Type: Engineering Fracture Mechanics; 13; 3, 19; 1980
    Format: text
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  • 9
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    Analysis of a unidirectional, symmetric buffer strip laminate with damage (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A method for predicting the fracture behavior of hybrid buffer strip laminates is presented in which the classical shear-lag model is used to represent the shear stress distribution between adjacent fibers. The method is demonstrated by applying it to a notched graphite/epoxy laminate, and the results show clearly the manner in which the most efficient combination of buffer strip properties can be selected in order to arrest the crack. The ultimate failure stress of the laminate is plotted vs the buffer strip width. It is shown that in the case of graphite-epoxy and S-glass epoxy laminates, the optimum buffer strip spacing to width ratio should be about four to one.
    Keywords: STRUCTURAL MECHANICS
    Type: Engineering Fracture Mechanics (ISSN 0013-7944); 20; 5-6; 801-811
    Format: text
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  • 10
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    Structural tests on space shuttle thermal protection system constructed with nondensified and densified Li 900 and LI 2200 tile (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Structural tests were conducted on thermal protection systems (TPS) LI 900 and LI 2200 tiles and .41 cm and .23 cm thick strain isolation pads. The bond surface of selected tiles was densified to obtain improved strength. Four basic types of experiments were conducted including tension tests, substrate mismatch (initial imperfection) tests, tension loads eccentrically applied, and pressure loads applied rapidly to the tile top surface. A small initial imperfection mismatch (2.29 m spherical radius on the substrate) did not influence significantly the ultimate failure strength. Densification of the tile bond region improved the strength of TPS constructed both of LI 900 tile and of LI 2200 tile. Pressure shock conditions studied did not significantly affect the TPS strength.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-81903
    Format: application/pdf
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