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Zhurkov, Bueche

Independently from each other Zhurkov et al. [45—47] in the USSR and Bueche [48—50] in the USA expressed the idea that in fracture of polymers — and also of metals for that matter — the breakage of primary (chemical) bonds plays an important role. They found that the time to fracture under uniaxial stress Gq of Zn, Al, and for example, PMMA and PS below their glass transition temperatures could be expressed by an exponential relationship involving three kinetic parameters  [Pg.56]

Equation (3.23) can be considered as a general expression of the kinetic nature of material disintegration. A closer discussion of the meaning of the molecular oscillation frequency, of the structure-sensitive parameter 7, and also of the activation [Pg.56]

For values of NCR 0.08 (thermoplastic materials) the correlation between mechanical properties and bond density is much less pronounced although the steep slopes of the shown curves tend to make the scatter of the actual data points less apparent. The main reason for the lack of good correlation certainly is the fact that in high polymer solids the stiffness and strength can be utilized only to that extent permitted by intermolecular attraction and segment orientation (cf. Table 1.1 for the differences in elastic moduli of chains, highly oriented fibers, and isotropic solids in section E below and in Chapter 5 the role of orientation and intermolecular attraction on chain strain is discussed in detail). [Pg.57]

In order to investigate the effect of the density of main chain bonds on the mechanical properties it is necessary to select experimental conditions such that [Pg.57]

In other words, in isotropic thermoplastics at the point of brittle failure only a minute fraction — less than 1% - of all main chain bonds is fully strained. Under these conditions, onset of unstable crack propagation is determined by the magnitude of intermolecular attraction. Reinterpreting Vincent s data one must say that it is not the number of backbone bonds er unit area and their accumulated strength [Pg.58]


A comparison of different reaction rate models was made by Henderson et al. [76] who found that the bond rupture theories (Tobolsky-Eyring, Zhurkov-Bueche) gave better agreement with fracture data on filled polybutadiene and filled and unfilled PVC than the bond slippage hypothesis. Primary uncertainties exist, however, with respect to a repair reaction and to the temperature dependence of jS and 7. The question of the true meaning of the activation volumes P and 7, of the stress ratio 0/ 0 > of the role of chain stretching and chain scission in macroscopic fracture will be resumed in Chapters 7 to 9. [Pg.64]

One of the most successful attempts to include the effects of temperature in a relatively simple expression similar to the one above, has been made by Zhurkov and Bueche using an equation of the form... [Pg.136]

There has been a prevailing theory that oxidative degradation is accelerated by mechanical stress [100]. This theory is based on fracture kinetic work by Tobolsky and Eyring [101], Bueche [102, 103, 104], and Zhurkov and coworkers [105, 106, 107]. Their work resulted in an Arrhenius-type expression [108] sometimes referred to as the Zhurkov equation. This expression caused Zhurkov to claim that the first stage in the microprocess of polymer fracture is the deformation of interatomic bonds reducing the energy needed for atomic bond scission to U=U0-yo, where U0 is the activation energy for scission of an interatomic bond, y is a structure sensitive parameter and o is the stress. [Pg.162]

The approach of Zhurkov and Bueche is an activation-volume argument in which the presence of the applied stress lowers the activation energy for chain scission, so increasing the value of the rate coefficient, k. The effect is to increase the prohahility, P, of scission of the central hond from Pq to (Casale and Porter, 1978)... [Pg.131]

A positive attempt to obtain a molecular understanding of Iracture took as its starting point the time and temperature dependence of the fracture process. This approach dates back to the early work of Bueche [90] and Zhurkov and co-workers [91]. It is assumed that the fracture process relates to the rate of bond breakage Vb at high stress, via an Eyring-type thermally activated process, so that... [Pg.309]

Eyring [44] considered the general decrease of secondary bonds, Zhurkov [45-47] and Bueche [48—50] that of primary bonds to be the strength controlling factor. [Pg.54]

Following the earlier works of Eyring, Zhurkov, and Bueche, these and other authors have continued to develop different aspects of the kinetic theory of fracture. Particularly in the USSR fracture data have been interpreted in terms of the failure of regular, nonmorphological model lattices (e.g., 54—58). Gubanov et al. [Pg.54]

In the fracture theory of Hsiao-Kausch [60, 61] the state of orientation of a polymeric solid is explicitly recognized. The theory combines the kinetic concept of Zhurkov or Bueche and the theory of deformation of anisotropic solids developed by Hsiao [59]... [Pg.59]


See other pages where Zhurkov, Bueche is mentioned: [Pg.459]    [Pg.40]    [Pg.56]    [Pg.459]    [Pg.459]    [Pg.40]    [Pg.56]    [Pg.459]    [Pg.117]    [Pg.212]    [Pg.339]   


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