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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of organic chemistry 46 (1981), S. 3696-3702 
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    International journal of fracture 66 (1994), S. 1-17 
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The problem of a mode I surface or internal crack in a plate with residual stresses is examined. The emphasis in this study is in accounting for crack surface contact. The importance of such problems is realized in both crack detection and in the stress intensity factor calculations. The line spring model is used to iteratively determine the border of the closed portion of the crack and the stress intensity factors along the open portion. It is demonstrated that the model is very versatile for solving contact problems. Examples for both surface and internal cracks are given. It is shown that if crack contact is ignored, the stress intensity factor may be significantly underestimated.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    International journal of fracture 68 (1994), S. 287-314 
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The problem of a surface or an internal crack in a plate which contains residual stresses is examined. The line spring model, which reduces a three-dimensional elasticity problem into a two-dimensional problem in plate theory, is used to model the crack. The Reissner plate theory, which takes into account transverse shear deformations, is used to model the plate. The formulation is based on Fourier Transforms which lead to a pair of singular integral equations that are solved numerically. The line spring method requires the plane strain solution to both the edge and internally cracked strip with crack surface loads representative of tension, bending, and the given residual stress distribution. For general use, plane strain solutions are presented for polynomial loading through the thickness up to the fifth order. Comparisons are made between the results given by the line spring model for the Reissner plate theory and the finite element method.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The Airy stress eigenfunction expansion of Williams [1] has been used to obtain simple expressions for the angular variations of the stress and displacement fields for n-material wedges and junctions subjected to inplane loading. This formulation applies to real and complex roots, as well as the special transition case giving rise to r −ω singular behavior. The asymptotic behavior of the general problem is similar to that of the bi-material interface crack. In the case of real roots, the stress and displacement expressions can be determined to within a multiplicative real constant (amplification), while for the complex case, the fields are determined to within a multiplicative complex constant (amplification plus rotation). Because of the rotation in the complex case, there are an infinite number of equivalent ways to express the angular variations (eigenfunctions) of the stress and displacement fields. Therefore, the fields are standardized in terms of ‘generalized stress intensity factors’ that are consistent with the bi-material interface crack and the homogeneous crack problems. As in the bi-material crack problem, for the complex case there are two stress intensity factors for each admissible order of the stress singularity. For specific n-material wedges and junctions, a small variation of material properties and/or geometry can change the eigenvalues from a pair of complex conjugate roots to two distinct real roots or vice-versa. An r −ω singularity associated with a nonseparable solution in υ and θ exists at this point of bifurcation. Such behavior requires an adjustment in the standard eigenfunction approach to insure bounded stress intensity factors. The proper form of the solution is given both at and near this special material combination, and the smooth transition of the eigenfunctions as the roots change from real to complex is demonstrated in the results. Additional eigenfunction results are provided for particular cases of 2 and 3-material wedges and junctions.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    International journal of fracture 90 (1998), S. 175-207 
    ISSN: 1573-2673
    Keywords: Nonlinear fracture ; interface crack ; mixed mode ; eigenvalue ; singular value decomposition.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A finite element formulation is developed for the analysis of variable-separable singular stress fields in power law hardening materials under conditions of plane stress. The displacement field within a sectorial element is assumed to be quadratic in the angular coordinate and of the power type in the radial direction as measured from the singular point. An iteration scheme that combines the Newton method and matrix singular value decomposition is used to solve the nonlinear homogeneous eigenvalue problem, where the eigenvalues and eigenfunctions are obtained simultaneously. The formulation and iteration scheme apply when the eigenvalue is complex. The examples considered include the single material crack and wedge to demonstrate convergence, and the bimaterial interface crack and the bimaterial wedge to demonstrate geometric versatility and the ability to handle complex eigenvalues. It is found that the real part of the complex eigenvalue for the interface crack agrees with the HRR value. In this case the associated complex eigenfunction is converted into an approximate real-valued eigenfunction that is valid for any mode-mix. In addition, the behavior of separable solutions near certain 'wedge paradox' geometries where non-separable solutions occur is investigated.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    International journal of fracture 94 (1998), S. 299-319 
    ISSN: 1573-2673
    Keywords: Nonlinear fracture ; HRR singularity ; mixed mode ; finite element analysis ; incompressible.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A displacement-based finite element formulation for the analysis of singular stress fields in power law hardening materials under conditions of plane strain is presented. The displacement field within a sectorial element is quadratic in the angular coordinate and of the power type in the radial direction as measured from the singular point. A hydrostatic pressure variable, which is linear in the angular coordinate, is introduced to account for the incompressibility of the material. The Newton method is combined with matrix singular value decomposition to iteratively solve the resulting nonlinear homogeneous eigenvalue problem where the eigenvalues and eigenfunctions are obtained simultaneously. The examples considered include the single material wedge, the bimaterial interface crack and the bimaterial wedge. In particular, the case of a single material wedge bonded to a rigid material along one edge is examined to study the possibility of the existence of mixed mode solutions for arbitrary wedge angles, including the important case of an interface crack when the wedge angle is 180 $$\circ $$ . This behavior is distinctly different from that of plane stress where a complex singularity is obtained. The possibility of the existence of nonseparable solutions is also discussed.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-1839
    Keywords: Computer simulation ; dissection ; anatomy ; morphology ; science education
    Source: Springer Online Journal Archives 1860-2000
    Topics: Natural Sciences in General , Technology
    Notes: Abstract Science teachers, school administrators, educators, and the scientific community are faced with ethical controversies over animal dissection in classrooms. Simulation has been proposed as a way of dealing with this issue. One intriguing previous finding was that use of an interactive videodisc dissection facilitated performance on a subsequent actual dissection. This study examined the prior use of simulation of frog dissection in improving students' actual dissection performance and learning of frog anatomy and morphology. There were three experimental conditions: simulation before dissection (SBD); dissection before simulation (DBS); or dissection-only (DO). Results of the study indicated that students receiving SBD performed significantly better than students receiving DBS or DO on both actual dissection and knowledge of the anatomy and morphology. Students' attitudes toward the use of animals for dissection did not change significantly from pretest to posttest and did not interact with treatment. The genders did not differ in achievement, but males were more favorable towards dissection and computers than were females.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1588-2837
    Keywords: Dichlorocyclopropanation ; 4-vinyl-1-cyclohexene ; phase transfer catalysis ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of regioselective dichlorocyclopropanation of 4-vinyl-1-cyclohexene has been studied under controlled phase transfer catalysis conditions, using aqueous sodium hydroxide as the base and 2-benzylidine-N,N,N,N′,N′,N′-hexaethylpropane-1,3-diammonium dibromide (Dq-Br) as a new phase transfer reagent. The reaction was carried out at 40 °C under pseudo-first order conditions by employing aqueous sodium hydroxide and chloroform in excess and was monitored by gas chromatography. The effect of various experimental parameters on the rate of the reaction has been studied and based on the experimental results, a suitable mechanism is proposed.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 38 (1995), S. 81-97 
    ISSN: 0029-5981
    Keywords: Singular fields ; Finite element formulation ; Eigensolution ; Multi-material junctions ; Antiplane ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A finite element formulation is developed to determine the order and angular variation of singular stress states at material and geometric discontinuities in anisotropic materials subject to antiplane shear loading. The displacement field of the sectorial element is quadratic in the angular co-ordinate direction and asymptotic in the radial direction measured from the singular point. The formulation of Yamada and Okumura14 for in-plane problems is adapted for this purpose. The simplicity and accuracy of the formulation are demonstrated by comparison to several analytical antiplane shear solutions for both isotropic and anisotropic multi-material wedges and junctions with and without disbonds. The nature and speed of convergence of the eigensolution suggests that the solution presented here could be used in developing enriched elements for accurate and computationally efficient evaluation of stress intensity factors in problems having complex global geometries.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 10
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