Tensile polymers under

It hag been shown that transition of a backbone carbon from the sp to sp state is promoted by tensile stresses and inhibited by compressive strains (10,44). The acceleration of the process of ozone oxidation of the polymers under load is not associated with the changes in supramolecular structure or segmental mobility of the chain. The probably reason of this effect is a decreasing of the activation energy for hydrogen abstraction (44). The mechanism of initial stages of the reaction of ozone with PP can be represented as ... 

Division of the total tensile strain under conditions of F = const into several components 25,6R,69) produced interesting results (see Fig. 8). It has been found that the behavior of molten low-density polyethylene (Fig. 8a) is qualitatively different from polyisobutylene (Fig. 8 b) the extension of which was performed under temperature conditions where the high-elasticity modulus, relaxation time, and initial Newtonian viscosity practically coincided (in the linear range) in the compared polymers. Flow curves in the investigated range of strain velocities were also very close to one another (Fig. 21). It can be seen from the comparison of dependencies given in Fig. 8a,... 

Inspite of a high band initiation stress Og, the resistance of PS to subsequent crack growth and final fracture is relatively low. The K -values of the crystalline polymers are much higher. A similar connection has also been established recently for various polymers under tensile test conditions... 

The approach taken in this section will be to consider in turn the empirical factors which govern the occurrence of molecular fracture and its consequences. The incidence of main-chain fracture in polymers under tensile stress is dependent on a wide range of variables, including polymer chemical structure, physical structure or morphology, additives, environment, time, temperature, orientation and physical state, as well as the more obvious variables of stress and strain. 

Molecular anchorages are of two main types crystalline regions and diemical cross-links (to which physical entanglements may also contribute in polym networks). Not surprisingly, then, most ESR studies of polymers under tensile stress have been carried out using crystalline fibres (nylon, PET, PE, PP for example) or cross-linked polymers ... 

The most extensive ESR studies of polymers under tensile load have undoubtedly been carried out on drawn crystalline fibres, and this work has been reviewed recently by Kausch and De Vries It is clear that the morpholines of oriented crystalline fibres, with extensive tie-chain populations and hn d rees of molecular uncoiling, strongly favour the incidence of molecular hracture under tensile stress. 

The effect of tensile draw on the "cluster" reflection is shown in Figure 12 and should be compared with Figure 7 for unhydrolyzed polymer. Under moderate strains, 1.75 times, it is seen that the "cluster" reflection is observed mostly in a direction normal to the strain. This is also true in the SAXS scan from fiber where the reflection is principally observed in the equatorial scan. This implies a periodicity which is normal to the fiber axis. Thus, the periodicity associated with this reflection tends to be orthogonal to the periodicity associated with the reflection observed in the meridional SAXS scan of unhydrolyzed fiber. Similar effects of sample orientation have recently been reported for ethylene-methacrylic acid ionomer (23). 

It will be shown in Chapter 11 that the correlations developed in this monograph can be combined with other correlations that are found in the literature (preferably with the equations developed by Seitz in the case of thermoplastics, and with the equations of rubber elasticity theory with finite chain extensibility for elastomers), to predict many of the key mechanical properties of polymers. These properties include the elastic (bulk, shear and tensile) moduli as well as the shear yield stress and the brittle fracture stress. In addition, new correlations in terms of connectivity indices will be developed for the molar Rao function and the molar Hartmann function whose importance in our opinion is more of a historical nature. A large amount of the most reliable literature data on the mechanical properties of polymers will also be listed. The observed trends for the mechanical properties of thermosets will also be discussed. Finally, the important and challenging topic of the durability of polymers under mechanical deformation will be addressed, to review the state-of-the-art in this area where the existing modeling tools are of a correlative (rather than truly predictive) nature at this time. 

Acoustic Emission of Polymers under Tensile Load... 

The simplest type of stress that can be applied to a polymer is a tensile stress, so the behaviour of polymers under such a stress is described before more general forms of stress are considered. This leads directly to a discussion of necking and cold drawing. 

In any case, experience tends to confirm the qualitative prediction of lower strengths for filled polymers under many circumstances [see Piggott and Leidner (1974) and also the discussion of fracture in Section 12.1.2.4]. For example, Wambach et al. (1968) found that the tensile yield strength of... 

When a tensile stress is applied to a polymer sample several mechanisms may contribute to changes in the vibrational spectrum of the polymer under examination. Thus, significant intensity variations can be observed as a consequence of phase transitions, strain-induced crystallization or orientation of the polymer chains. Apart from these effects it has been demonstrated in a series of investigations on the molecular mechanics of stressed polymers, both theoretically and experimentally, that the frequency and shape of absorption bands — predominantly those which contain contributions of skeletal vibrations — are stress sensitive This sensitivity of molecular vibrations to mechanical stress has been interpreted in terms of different mechanisms such as quasielastic deformation (reduction of force constants due to bond weakening under stress), elastic bond stretching or angle bending and conformational varia-... 

Rgurel.18 Different deformation zones in polymers under tension loading, showing tensile bars after loading and the light optical appearance of the deformation area (left), as well as schematic illustrations of the micromechanical structures and macromolecular mechanisms (right)... 

Polymers Under Tensile Load - Adv. Polymer Sci. Engineering, Ed. by K. D. Pae, D. R. Morrow, and Y. Chen, Plenum Press,... 

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