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  • 1
    ISSN: 1436-5057
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Direkte Methoden zur Lösung von singulären Integralgleichungen vom Cauchy-Typus (S. I. G.) beruhen auf der Gaussschen Regel für numerische Integration, wobei die S. I. G. durch Anwendung der resultierenden Funktionalgleichung an geeignet gewählten Kollokationspunkten auf ein lineares Gleichungssystem reduziert wird. In diesem Artikel wurde die Äquivalenz dieser Methode mit derjenigen, welche auf der Lagrangeschen Interpolations-Approximation der unbekannten Funktion, beruht, gezeigt. Indirekte Methoden zur Lösung von S. I. G. können durch Anwendung derselben numerischen Regel an der Fredholmschen Integralgleichung, auf welche die S. I. G. reduziert wird, erhalten werden. In diesem Artikel wurde gezeigt, daß beide Methoden, im Sinne, daß sie dieselben numerischen Resultate liefern, äquivalent sind. Schließlich wurde mit Hilfe dieser Resultate der, Fehler und die Konvergenz der Methoden festgestellt.
    Notes: Abstract Direct methods for solving Cauchy-type singular integral equations (S.I.E.) are based on Gauss numerical integration rule [1] where the S.I.E. is reduced to a linear system of equations by applying the resulting functional equation at properly selected collocation points. The equivalence of this formulation with the one based on the Lagrange interpolatory approximation of the unknown function was shown in the paper. Indirect methods for the solution of S. I. E. may be obtained after a reduction of it to an equivalent Fredholm integral equation and an application of the same numerical technique to the latter. It was shown in this paper that both methods are equivalent in the sense that they give the same numerical results. Using these results the error estimate and the convergence of the methods was established.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Computing 31 (1983), S. 105-114 
    ISSN: 1436-5057
    Keywords: Primary 65D30 ; 65D32 ; secondary 41A55 ; Cauchy-principal values ; finite-part integrals ; convergence ; Jacobi quadratures ; Lagrange polynomials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung In diesem Artikel sind hinreichende Bedingungen, welche die Konvergenz von Quadratursätzen des Elliott-und Hunter-Typus für die Bestimmung von gewichteten Cauchy Hauptwert-Integralen der Form sicherstellen, hergeleitet. Die gleichzeitige Konvergenz beider Quadraturen im Intervall (−1, +1) wurde für eine Klasse von Hölderstetigen Funktionenf(f∈H μ ) nachgewiesen. Im Artikel sind auch Korrekturen von gewissen früheren Darlegungen über die Konvergenz von solchen Quadraturen enthalten. Ferner wurde eine einfache Herleitung der Elliott-und Hunterschen Quadratursätze für die Bestimmung derp-ten Ableitung des obenstehenden Integrals gegeben und hinreichende Bedingungen für die Konvergenz der Hunterschen Quadratur wurden erhalten. Die Konvergenz dieses Integrals wurde somit für Funktionenf, für welchef (p) ∈H μ gilt, sichergestellt.
    Notes: Abstract In this paper sufficient conditions are derived to ensure the convergence of the Elliott and Hunter types of quadrature rules for the evaluation of weighted Cauchy principal-value integrals of the form: The simultaneous convergence in the interval (−1, 1) of both quadratures was established for a class of Hölder-continuous functionsf(f∈H μ ). Corrections of some previous statements on the subject of convergence of such quadratures are also included. Moreover, a simple derivation of the Hunter and Elliott types of quadrature rules for the evaluation of the derivative of thep-th-order of the abovestated integral was given and sufficient conditions for the convergence of the Hunter-type quadrature were obtained. Thus, the convergence of this integral was ensured for functionsf such thatf (p) ∈H μ .
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary The role of the boundary interphase on the adhesion efficiency between fiber and matrix in the case of polymers reinforced with unidirectional fibers was investigated. A theoretical model was introduced considering that the composite material consists of three phases; that is, the fiber, the matrix and the interphase, material which is the part of the polymer matrix lying at the close vicinity of the fiber surface. The interphase material, having different physical properties from those of the bulk matrix, affects the overall behavior of the composite. Moreover, the quality of adhesion between the two main phases depends greatly on the nature of the interphase material. In this study we have considered that the interphase material is inhomogeneous in nature, with properties varying continuously from the fiber surface to the bulk matrix. The theory developed resulted in a criterion of the adhesion quality and in a prediction of the longitudinal modulus of elasticity of the fiber-composite.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 261 (1983), S. 825-833 
    ISSN: 1435-1536
    Keywords: Polymers ; Slow-brittle-fracture ; Toughness ; Caustics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A slow crack growth was achieved in initially edge-cracked specimens made of a high-molecular weight PMMA by regulating the cross-head speed of loading by a computer-driven testing machine. The strain rate $$\dot \varepsilon $$ used during the tests varied between $$\dot \varepsilon $$ =1× l0−6 s−1 and 1×10−4 s−1. It was shown that, in this zone of slow quasi-static loading of brittle polymethylmethacrylate specimens under conditions of plane stress, the crack initiated for a critical value of loading, at some characteristic zone of strain-rate variation at the crack tip. It was established that for strain rate between $$\dot \varepsilon $$ =0.18×10−5 s−1 and $$\dot \varepsilon $$ =0.45×10−4 s−1 brittle cracks were propagating always slowly with velocities in the range ofc=3 to 5×10−2 m/s. For values ofv s outside this transition zone fracture was typically brittle with high crack-propagation velocities. As the strain rate was varying beyond the stable low-velocity region, a two-step crack velocity pattern was operative, where the one step took always low values, and the other step corresponded to crack-propagation velocities significantly higher than these limits, tending to typical brittle-fracture velocities of the material. Oscillations of the velocityc at the transition zones, or, in many cases all over the zone of slow propagation of the crack, indicated the unstable character of crack propagation, influenced by different stress raisers and especially by the opposite longitudinal boundary of the specimen. Stress intensity factor values during crack propagation, evaluated from the front (cuspoid) and the rear (external) caustic, which remained alwaysk g-dominant, were following similar trends as the variation of the crack propagation velocity.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 262 (1984), S. 929-938 
    ISSN: 1435-1536
    Keywords: Fibrous composites ; mesophase ; unfolding models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A theoretical model was introduced for the evaluation of the boundary layer developed between the main phases during the preparation of unidirectional fiber composites. It has been shown that this thin layer influences considerably the physical properties of the composite. It was assumed that the physical properties of themesophase unfold from those of the hard-core fibers to those of the softer matrix. Thus, a multicylinder model was assumed improving the classical two-cylinder model introduced by Hashin and Rosen for the representative volume element of the composite. Based on thermodynamic phenomena appearing at the glass transition temperatures of the composite and concerning the positions and the sizes of the heat-capacity jumps there, as well as on the experimental values of the longitudinal elastic modulus of the composite, the extent of the mesophase and the mechanical properties of the composite may be accurately evaluated. This version of the model is based on a previous one concerning a multilayer model, but it is considerably improved in order to take into consideration, in a realistic manner, the physical phenomena developed in fiber reinforced composites.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 258 (1980), S. 1044-1051 
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary A theoretical expression of the value of the glass-transition temperatureT g at any direction of orientation, defined by the angle ϑ subtended between this direction and the average axis of fibers; was introduced. Dilatometric, as well as dynamic tests were executed for a type of unidirectional composite in order to compare the respective values ofT g derived from these tests. The experimental results were also compared with theoretical values derived from the theoretical expression. A satisfactory agreement between, theory and experiment was established.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 260 (1982), S. 837-841 
    ISSN: 1435-1536
    Keywords: Adhesion coefficient ; composites ; fibers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A theoretical model, consisting of a series of infinite concentric cylinders surrounding a fiber in a composite material, was introduced in this paper to give a quantitative account of interface phenomena, already experimentally observed. A series of specimens, conveniently designed to represent the theoretical model, were subjected to dynamic modes of loading to measure the amount of adhesion between fibers and matrices by means of an adhesion coefficient developed in the theory. It was found that theoretical results for the adhesion between matrix and filler were compatible with the structural characteristics of the specimens tested.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 262 (1984), S. 867-875 
    ISSN: 1435-1536
    Keywords: Polyimides ; polymers ; ductile fracture ; caustics ; K I -factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The mechanical and optical properties of polyimides were studied in this paper and the influence of the variation of the reaction temperature on the physico-chemical properties of the polymers was evaluated. From this the dependence of the stress-strain diagrams on the reaction temperature, as well as the stresses and strains at fracture were experimentally determined. Moreover, the elastic moduli and Poisson's ratios, as well as the refractive index of the polymers were evaluated for different temperatures of imidization. In order to define also the behaviour of the polymers as thin membranes at fracture, simple tension tests with edge-cracked thin strips were executed up to fracture. The method of caustics was used, with the specimens loaded inK I mode of deformation at different stress-levels to evaluate the stress intensity factors of the materials in the non-linear zone of loading. TheK I -factor was evaluated by applying the simple Dugdale-Barenblatt model for the ductile materials, whereas for brittle samples the elastic theory was used. Interesting results concerning the physico-mechanical properties of the polyimides were derived.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 261 (1983), S. 394-403 
    ISSN: 1435-1536
    Keywords: Moisture absorption ; particulates ; composites ; glass transition temperatured
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Water absorption in particulate composites at ambient temperature influences their thermomechanical properties. Second Fick's law of diffusion was used in this paper to predict the diffusion coefficient of the composite materials tested. In all cases the matrix material was a diglycidyl ether of bisphenol-A polymer cured with 8 phr triethylene tetramine and filled with iron particles with an average diameter 150 μm at five distinct volume fractionsv f =0, 0.05, 0.10, 0.16 and 0.20. The modification of the modulus of elasticity, ultimate stress, breaking strain and breaking energy due to moisture absorption was examined. Moreover, differential scanning calorimetry was used to study the influence of the time exposure into water and the filler concentration of the particulates on their glass transition temperature. Finally, the void occupancy in the composite was evaluated from free volume considerations.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 53 (1983), S. 225-241 
    ISSN: 1432-0681
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Übersicht Komplexe Potentiale Φ(z) und Ψ(z) werden berechnet. Sie beschreiben das Intensitätsfeld, das von einer Einzelkraft oder von einer Versetzung hervorgerufem wird. Diese Potentiale werden angewandtauf einige Punkte innerhalb jeder der Halbebenen, die auf verschiedene Art und Weise miteinander verbunden sein können. Bei Verwendung dieser Potentiale in Form von Greenschen Funktionen haben wir das Problem der Risse und/oder der Löcher, die in jeder Halbebene enthalten sind, auf eine Integralgleichung für diese Risse oder Löcher reduziert. Der Vorteil dieser Methode ist der, daß dabei die Integralgleichung, angewandt auf die Grenzfläche zwischen den beiden Halbebenen (y = 0), überflüssig wird. Somit wird die numerische Berechnung des Intensitätszustandes weitgehend vereinfacht. Es wurden die betreffenden Integralgleichungen hergeleitet, die einigen charakteristischen Fällen von zweimaterialigen Platten entsprechen. Die Beispiele von rißenthaltenden Halbebenen, jede von ihnen intensitäts- oder versetzungsfrei oder verbunden mit anderen Halbebenen, zeigen die Leistungsfähigkeit dieser Methode.
    Notes: Summary The complex potentials Φ(z) and Ψ(z) describing the stress-field due to a concentrated force, or a dislocation, applied at some point at the interior of either of the half planes bonded together, or being under some kind of contact between them, are calculated. By using these potentials as Green's functions we have reduced the problem of crack and/or holes existing in either of these half-planes to an integral equation along the cracks or holes. The advantage of the method is that the integral equation along the interface between the two half-planes (y=0) is canceled out. Thus, the numerical evaluation of the state of stress is considerably reduced and simplified. The respective integral equations corresponding to some characteristic cases of bimaterial plates were derived. Finally, examples of cracked half-planes, either stressor displacement-free, or bonded with other half-planes, indicated the potentialities of the method.
    Type of Medium: Electronic Resource
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