Plasticity fractal concept

As it has been shown above using position spectroscopy methods [22], the yielding in polymers is realized in densely packed regions of their structure. Theoretical analysis within the frameworks of the plasticity fractal concept [35] demonstrates that the Poisson s ratio value in the yielding point, can be estimated as follows ... 

Let us consider, which processes result to necessary for yielding realization fluctuation free volume increasing. Theoretically (within the frameworks of polymers plasticity fractal concept [35] and experimentally (by positrons annihilation method [22]) it has been shown, that the yielding pro-... 

The value % can be determined within the frameworks of polymers plasticity fractal concept [35] according to the Eq. (4.9). The dependence of on shows increasing at growth [102]. At small values all crystallites are subjected to disordering owing to that yield tooth in BPE curves stress-strain is absent and these curves are acquired the form, which is typical for rubbers. Hence, stress decay beyond yield stress intensification is due tox growth [103],... 

Independent checking of the accuracy of quantitative estimations of values of 5 and can be carried out as follows. Within the frameworks of the plasticity fractal concept [38, 39] and the cluster model of the amorphous state structure of polymers [5, 6] it has been shown that the yield process is realised in densely packed regions of the structure (clusters). In addition, the relative fraction of the clusters is equal to the yield process realisation probability (1 -%) [39]. The probability (1 x) calculation method is given in paper [39] and the value

[Pg.211]

It was also found [6], that in this case experimentally determined values of athermic fracture stress turn out to be essentially (2 3 times) smaller than theoretically calculated ones. A small values k 0.2 1.0) is one more important feature of nonoriented polymers fracture in impact tests. This means, that the stress on breaking bonds is essentially lower than nominal fracture stress of bulk sample. And at last, it was found out [7], that the value k reduces at testing temperature growth and the transition from brittle fiactuie to ductile (plastic) one. These effects explanation was proposed in Refs. [4-7], but development of fractal analysis ideas in respect to polymers lately and particularly, Alexander and Orbach woik [8] appearance, which introduced the fraction notion, allows to offer the major treatment of polymer fracture process [9, 10], including the dilaton concept [1-3] as a constituent part. 

---