Visco-elastic behaviour

Assuming T>Tg for reversible flow processes (visco-elastic behaviour) Eq. (32) yields... 

Here r is a characteristic time constant, usually called the dielectric relaxation time. To conform to analogous theories of visco-elastic behaviour we should really use the term dielectric retardation time, because it refers to a gradual change in a strain (the polarisation or resulting electric displacement) following an abrupt change in stress (the applied field). Dielectric relaxation time is, however, still most commonly used in spite of this inconsistency. By integration of Equation (3.12) ... 

Within the region of linear visco-elastic behaviour, an imposed stress of angular frequency, u>, results in a harmonic strain of amplitude proportional to the stress amplitude, and with phase lag 8 relative to the stress, which is independent of the applied stress amplitude [Ferry, 1980],... 

Fenijn J. and R.C. Krooshof. 1970. The sliding plate rheometer. A simple instrument for measuring the visco-elastic behaviour of bitumens and related substances in absolute units. Proceedings of the 9th Annual Conference CTAA, Vol. 15, p. 123. 

Creep. In general, polymers exhibit a degree of visco-elastic behaviour and thus for full characterisation of such a material a knowledge of its rate dependent response is necessary. To determine the long-term behaviour of a material either stress relaxation or creep tests may be used. The former involves monitoring the time-dependent change in stress which results from the application of a constant strain to a specimen at constant temperature. Conversely,... 

The above-mentioned complexity of the relationships between the structure and properties of textiles is further complicated by the non-linear mechanical properties of individual fibres caused by their visco-elastic behaviour, friction between fibres and threads, anisotropy, and statistical distribution of all properties. Modelling such complex materials requires application of a combination of experimental, analytical, and numerical methods, which will be considered in this chapter. 

O3, h). .. etc. from this family of curves, which form the relaxation curve. Furthermore, by determining the stress which belongs to a specified strain in the relaxation test after a long test time, one can experimentally verify the only calculated tensile test stress-strain-curves for very small deformation rates. The isochronous stress-strain diagram also directly indicates the non-linearity of the visco-elastic behaviour otherwise the curves would be straight lines. 

The calculation of the characteristic deformations of visco-elastic behaviour. Table 3,107, reveals their dependence to the solicitation conditions. The maximal difference was recorded for the stretched and concomitantly accelerated aged sample. The sample firstly accelerated aged presents a maximal value and its residual... 

Duquesne, S. Le Bras, M. Delobel, R. Visco-elastic behaviour of intumescent systems, in M. Lewin, Ed., Proceedings of the Conference on Recent Advances in Flame Retardancy of Polymeric Materials, Norwalk, CT, 2002, pp. 50-64. 

However, one important energy loss which was explained was the effect of the visco-elastic behaviour of the polymer [35]. This was studied by varying the cross-link density of the rubber, to alter the loss of elastic energy as the material relaxed. As the viscoelastic loss increased, so did the adhesive hysteresis, as shown in Fig. 35. 

Other types of network defect also exist physical crosslinks and closed loops (Fig. 3.16). Physical crosslinks may be permanent with a locked-in conformation (Fig. 3.16(a)) of temporary by entanglement. The presence of the latter type leads to visco-elastic behaviour, i.e. to creep and stress relaxation. Intramolecular crosslinks decrease the interconnectivity and reduce the number of loadcarrying chains. 

The visco-elastic behaviour of glasses can be described by Maxwell s law (1.4) [383] ... 

Non-Newtonian flow and visco-elastic behaviour of flocculated systems. . 356... 

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