Construction of the nonlinear relations of thermoviscoelasticity

Koltunov, M. A.

doi:10.1007/bf00858735

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“…The procedure of plotting creep isochrones is outlined in [6,11,12]. Figure 4 shows creep isochrones for microplastic (a) and organic plastic (b) plotted from the experimental creep curves borrowed from [15].…”

Section: Linearity Of Viscoelastic Properties From Creep Isochronesmentioning

confidence: 99%

mentioning

confidence: 91%

“…It is represented by an infinite series of multiple integrals; therefore, it is not practical to identify numerous kernels and to determine their parameters experimentally. Similar difficulties arise in using the nonlinear models proposed in [4,6,7,10,13,22].The approach based on the similarity of creep isochrones [11,12,[17][18][19][20] appears to hold more promise for nonlinear models of viscoelasticity. This approach was further developed in [27] by augmenting the similarity condition to include the instantaneous strain curve as an isochrone for time zero.…”

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confidence: 94%

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Nonlinear creep of unidirectional fibrous composites tensioned along the reinforcement

2007

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Creep strains in unidirectional organic-fiber-and organic-glass-fiber-reinforced plastics subject to tension in the reinforcement direction are predicted. Based on homogeneity condition and statistical criteria, it is shown that the creep of the composites is essentially nonlinear. To predict creep strains, use is made of a nonlinear creep model based on a modified Rabotnov's similarity hypothesis for isochrones and of material constants determined from tests on specimens made of a composite as a whole and specimens made of its separate components, the mixing rule applied in the latter case. The calculated results and the experimental data are in satisfactory agreement Introduction. Many unidirectional fibrous composites are engineering materials in which a viscoelastic matrix is reinforced with various organic and inorganic fibers. These composites are widely used in aeronautical and space engineering, shipbuilding, oil refinary, and oil and gas pipelines [1,8,14,21,23]. Fibrous composites as reinforcement of concrete structures have recently aroused considerable interest [26,32].Under long-term loads, viscoelastic fibrous composites creep even at temperatures far below the glass-transition temperature. This effect necessitates using creep strain, creep rate, relaxation time, creep limits, and long-term strength as the main deformation and strength characteristics of composites. One of the important problems in the mechanics of viscoelastic composites is to predict their viscoelastic properties from the properties and volume fractions of its components.A great many theoretical and experimental studies are concerned with various aspects of creep in unidirectional fibrous composites. Some of the results from such studies are reviewed in [8,9,14,15,23,30]. It should be noted that the overwhelming majority of studies deal with the linear range of long-term viscoelastic deformation. All solutions found are based on the Boltzmann-Volterra theory of linear viscoelasticity [11,31]. When used to predict creep strains of composites from the properties of their components, the linear theory is usually supplemented with the mixing rule [8,14,15,23].Theoretical and experimental studies of creep of various polymer composites show that the linear theory of viscoelasticity can be directly applied to a certain class of problems. In the majority of composites, however, the range of linearity is relatively short, and satisfactory results can only be obtained with not too high stresses and short-term loads. It should be taken into account that a portion of the creep strain may be irreversible.There are several approaches to describe the nonlinear viscoelastic deformation of composites. The general nonlinear equation of viscoelasticity was derived in [33]. It is represented by an infinite series of multiple integrals; therefore, it is not practical to identify numerous kernels and to determine their parameters experimentally. Similar difficulties arise in using the nonlinear models proposed in [4,6,7,10,13,22].The approach based on ...

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Section: Linearity Of Viscoelastic Properties From Creep Isochronesmentioning

confidence: 99%

mentioning

confidence: 91%