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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 256 (1978), S. 625-630 
    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 thermomechanical behaviour of a particle composite was evaluated under the assumption that a boundary interphase between the matrix and the filler particles develops, upon the thermomechanical properties of which the overall behaviour of the composite depends. This interphase exists in reality and it contains both areas of adsorption interaction in polymer surface layers onto filler particles as well as areas of mechanical imperfections. Under the assumption that the interphase is homogeneous and isotropic exhibiting perfect adhesion with both main phases a theory was developed providing quantitative means of assessing the adhesion efficiency between the phases and its effect on the thermomechanical behaviour of the composite. Experimental results are in good agreement with theoretical predictions.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 264 (1986), S. 561-569 
    ISSN: 1435-1536
    Keywords: Fibrous composites ; mesophase ; longitudinal elastic modulus ; transverse elastic modulus ; major Poisson ratio
    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 Expressions for the evaluation of the transverse and longitudinal elastic moduli and the major Poisson ratio of unidirectional fiber composites are derived. The model described is based on the correct version of Kerner's model, which in our case is conveniently modified by introducing a mesophase layer between the fiber and the matrix in the representative volume element surrounding the typical fiber. The expression for the longitudinal elastic modulus derived in this paper, and the law of mixtures already presented in previous papers, give concordant results. Therefore, the law of mixtures, taking the mesophase also into account, and the two-term unfolding model for the mesophase are used for the evaluation of its extent and its properties. The model was applied to a glass filament-epoxy resin composite and its predictions were found to be in good agreement with the experimental data.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 215 (1967), S. 149-157 
    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
    Description / Table of Contents: Zusammenfassung Ein Programm, bei dem ein vernetztes Polymeres mit diskontinuierlichen Sprüngen von gleichem zeitlichem Abstand und konstanter Amplitude in bezug auf Dehnung oder Spannung belastet wird, kann höhere Näherungen für Retardations- und Relaxationsspektra mit einem ausreichenden Grad an Genauigkeit liefern, vorausgesetzt, daß dasBoltzmannsche Superpositionsprinzip nicht verletzt wird. Im Falle der Retardationsspektren ist die Mehrstufenbelastung ersetzbar durch eine anfängliche Kriechbelastung, gefolgt durch Stufen der Entlastung mit gleichen Amplituden und gleichen Zeitabständen. In dem Fall, daß eine exakte Master-Kurve für das Material durch Anwendung des Prinzips der reduzierten Variablen erlangbar ist, gewährt diese Kurve genügend Information für die Ermittlung des Retardationsoder Relaxationsspektrum mit ausreichender Näherung. Beispiele werden für die Gewinnung von Retardations- und Relaxationsspektren bis zu ihrer dritten Näherung für ein Epoxidharz und für ein Polyurethan-Elastomeres unter Verwendung der Mehrstufenmethode gegeben. Drei Näherungen der Relaxationsspektren für N.B.S., Polyisobutylen und Polymethylmethacrylat werden aus den Master-Kurven abgelcitct.
    Notes: Summary A multistep loading programme for a cross-linked polymer with equidistant discontinuities jumping with constant amplitudes of stress or strain may yield higher approximations of the retardation or relaxation spectra to any degree of accuracy provided that theBoltzmann superposition principle is not violated. In the case of retardation spectra the multistep loading programme can be replaced by an initial creep loading followed by steps of recovery of equal amplitudes and time. In the case when an accurate composite curve of the material is available by application of the principle of reduced variables, this curve yields sufficient information for the tracing of retardation or relaxation spectra to any degree of approximation. Examples are given for the tracing of retardation and relaxation spectra up to their third approximation for an epoxy polymer and a polyurethane elastomer by using the multistep method. Three approximations of relaxation spectra for N.B.S. Polyisobutylene and Polymethylmethacrylate are also derived from their composite curves.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Rheologica acta 25 (1986), S. 350-358 
    ISSN: 1435-1528
    Keywords: Composite ; elastic modulus ; mesophase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract A theoretical model for the evaluation of the elastic modulus in particulate composites has been developed. The method takes into account the existence of a mesophase between main phases, which constitutes an important parameter influencing the behaviour of a composite material. This layer between the matrix and filler develops different physico-chemical properties from those of the constituent phases and variable ones along its thickness. The effect of the progressive variation of the elastic modulus of the mesophase on the modulus of the composite was estimated by applying various simple laws of variation. Convenient laws of variation were introduced, varying from a simple one, assuming a linear law, to a more refined one using a parabolic law. Experimental results with particulates, based on iron-filled epoxy composites, compared satisfactorily with other models. However, the model based on a parabolic law was superior to all others on physical grounds.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Rheologica acta 26 (1987), S. 182-192 
    ISSN: 1435-1528
    Keywords: Transverseshear modulus ; unidirectionalfiber composite ; mesophase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract A new relation for the prediction of the transverse shear modulus in unidirectional fiber composites has been derived. The theoretical results of this relationship are in better agreement with the experiments than those of other relations, existing in the literature. The discrepancies, which are observed among the theoretical predictions and the experimental values, are explained by the consideration of the boundary layers existing between the matrix and the fibers of the composite. A new model, which includes the intermediate phase between the matrix and the fiber, called the mesophase, is considered in order to take into account the above-mentioned layers.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Rheologica acta 6 (1967), S. 246-251 
    ISSN: 1435-1528
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Summary Transient creep recovery tests in simple tension were performed in a series of cross-linked high polymers in pure and plasticized states. A loading cycle was adopted according to which each specimen was loaded in creep for a time period of 16′ followed by recovery for the same time period. This loading cycle was repeated for various steps of temperature from ambient temperature up to a temperature corresponding to the rubbery region of each polymer. It was shown that, while the 15″ measurements of deformation after loading or unloading were approximately equal, recovery individual curves were always lagging in time the corresponding creep curves. Composite curves of creep or recovery deformation in semi-log time scale reduced to a temperature of 30 °C were plotted by applying the method of reduced variables. The creepdeformation composite curve was always advancing in time relatively to the respective recovery composite curve. This phenomenon was an accumulation of the partial difference of the corresponding individual curves. Time-shift factor versus temperature curves for creep and recovery were plotted and compared. It was established that the remaining deformation after 16 minutes of a 16′ creep recovery normalized to the initial deformation at the beginning of recovery, if plotted versus temperature, presented the same shape of curves for all types of materials tested. The maxima of these curves were diminishing with addition of plasticizer according to a straight line.
    Type of Medium: Electronic Resource
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  • 7
    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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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Rock mechanics and rock engineering 32 (1999), S. 267-290 
    ISSN: 1434-453X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Summary Experimental evidence from true triaxial tests on dense rocks are analysed with emphasis on the failure modes of these materials under multiaxial loading, ambient temperature and external pressure. The strong dependence of the modes of fracture on the secondary components of applied stresses, and especially on the intermediate principal stress, indicated that the failure surface of these brittle materials may be appropriately described by a failure tensor polynomial criterion. As such, the elliptic paraboloid failure criterion was found to conveniently describe their mode of failure, by considering also the severe influence of anisotropy of the material.  For this purpose, a method developed recently (Theocaris and Panagiotopoulos, 1995a, 1995b) was applied, defining anisotropic hardening plasticity through an appropriate sequence of anisotropic elasticity problems. Assuming a particular path of loading or unloading, we measured the instantaneous tension and compression yield stresses along the transient principal-stress directions. These parameters completely define the instantaneous state of anisotropy of the body for the corresponding loading step, by applying the theory of the elliptic paraboloid failure locus (EPFS) (Theocaris, 1989a). A parameter identification problem was formulated on the constitutive expressions for this most general failure criterion. Then, by applying convenient constraints derived from the EPFS theory, which serve as filters throughout the whole procedure, the characteristic values of terms defining the variable components of the failure tensor polynomial were calculated, as the material was continuously loaded from the elastic into the plastic region and up to the ultimate failure load. Accurate simple tests in uniaxial tension and compression provided sufficient data for the definition of the yield loci of the material, at the considered loading step. These tests may be complemented with biaxial and triaxial modes of loading of the specimens. The results improve the accuracy and sensitivity of the method. All such data were used as input values, for establishing the mode of plastic deformation of the body during particular loading paths.  Moreover, the method employed allows the complete definition of the components of the failure, H, and the strength differential effect, h, tensors at each loading step. These quantities define completely the failure tensor polynomial for each material. Therefore, it presents the important advantage over other experimental methods by clearly indicating the parts contributed to the failure mode (either by plasticity, or by the strength differential effect) and their evolution during plastic deformation.  As convenient prototype materials for testing the method, specimens of metamorphic rocks such as Westerly granite (G), or quartzite (Q) were selected. Interesting results concerning the mechanical and especially the failure modes of such materials were obtained. Furthermore, the mechanical tests indicated clearly some basic properties of these materials as concerns the mode of their structure.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Acta mechanica 87 (1991), S. 219-238 
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The experimental method of reflected causties was extended in this paper for the study of the strength of the plastic singularity and the respective plastic stress intensity factor at the tip of a mode-I crack in an elastic-strain hardening material. The elastic-plastic field around the crack tip was defined by means of the singular plastic solutions of Hutchinson, Rice and Rosengren (HRR-asymptotic field) which gives satisfactory results for small scale yielding types of deformation. The initial curve, generating the caustic by reflection from the front face of the deformed specimen lying well within the plastic zone, was accurately determined by considering the contribution of the elastic and plastic components of stresses and strains within the plastic zone. Results with experiments executed on steel specimens single-edge notched with various values of the hardening exponentn coincided with the form and shape of the theoretically derived caustics thus confirming the validity of the developed theory. The values of the plastic stress intensity factor thus derived corroborated the already existing results from previous experiments.
    Type of Medium: Electronic Resource
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