Stress-strain behavior elastomers

The influence of ambient aging at 70°F and accelerated aging at 160°F on the stress-strain behavior of carboxy-terminated polybutadiene, polybutadiene-acrylic acid, polybutadiene-acrylic acid-acrylonitrile, and hydroxy-terminated polybutadiene composite propints is shown in Figures 10 and 11. The elastomers and curative agents for these formulations are listed below... 

Figures 4 and 5 show the stress-strain behavior of reinforced elastomers and toughened plastics, respectively. In each case, the corresponding homopolymers are included for comparison. In...

FIGURE 14.6 Typical stress-strain behavior for fibers, plastics, and elastomers. 

It was shown, on the one hand, that gum-filler interactions are associated with the immobilization of a certain amount of rubber on the surface or inside the carbon black aggregates, and, on the other hand, that the corresponding bound or occluded rubbers play important roles in the reinforcement process due either to a restriction of elastomer chain mobility in the vicinity of the filler or to an increase of the effective volume of the latter. What are now the effects exerted by a filler on the stress-strain behavior and the modulus of cured rubbers ... 

Quested et al. [16] have conducted an extensive experimental program on the stress-strain behavior of the elastomer solithane while subjected to an ambient at high pressure. Some of their experimental results are reproduced in Fig. 13. (Note that the reported stress is the deviatoric, not the total, stress as observed from the fact that the reported stress is zero for X = 1 for the various imposed ambient pressures). For the classic ideal affine network model (all stress caused by ideal Nc Gaussian chains in a volume v with no nonbonded interactions)... 

Thermosets are polymeric materials which when heated form permanent network structures via the formation of intermolecular crosslinks. Whether the final product has a glass transition temperature, Tg, above or below room temperature, and therefore normally exists as an elastomer or a glass, it is, strictly speaking, a thermo-set. In practice, however, thermosets are identified as highly crosslinked polymers that are glassy and brittle at room temperature. These materials typically exhibit high moduli, near linear elastic stress-strain behavior, and poor resistance to fracture. 

Fig. 11). It is, therefore, highly probable that the bulky filler particles impose geometrical hindrances (entropy constraints) for the chain dynamics at the time scale of the NMR experiment (of the order of 1 ms). This effect may be compared with the effect of transient chain entanglements on chain dynamics in polymer melts. It should be remarked that the entanglements density estimated for PDMS melts by NMR is close to its value fi om mechanical experiments [38]. Therefore, it can be assimied that topological hindrances from the filler particles can also be of importance in the stress-strain behavior of filled elastomers. 

It appears that the following peculiarities of the network structure in the elastomer matrix outside the adsorption layer are of importance for a molecular understanding of stress-strain behavior for these materials ... 

The stress-strain behavior of thermosets (glassy polymers crosslinked beyond the gel point) is not as well-understood as that of elastomers. Much data were analyzed, in preparing the previous edition of this book, for properties such as the density, coefficient of thermal expansion, and elastic moduli of thermosets [20,21,153-162]. However, most trends which may exist in these data were obscured by the manner in which the effects of crosslinking and of compositional variation were superimposed during network formation in different studies, by... 

The equilibrium small-strain elastic behavior of an "incompressible" rubbery network polymer can be specified by a single number—either the shear modulus or the Young s modulus (which for an incompressible elastomer is equal to 3. This modulus being known, the stress-strain behavior in uniaxial tension, biaxial tension, shear, or compression can be calculated in a simple manner. (If compressibility is taken into account, two moduli are required and the bulk modulus. ) The relation between elastic properties and molecular architecture becomes a simple relation between two numbers the shear modulus and the cross-link density (or the... 

The distinction between plastics, fibers, and elastomers is most easily made in terms of the tensile stress-strain behavior of representative samples (Rudin, 1982). The curves shown in Fig. 1.17 are typical of those obtained in tension for a constant rate of loading. The parameters of each curve are normal stress (force applied on the specimen divided by the original cross-sectional area), nominal strain (increase in length divided by original length), and the modulus (slope of stress-strain curve). The slope of the curve near zero strain gives the initial modulus. 

Although the dynamic mechanical properties and the stress-strain behavior iV of block copolymers have been studied extensively, very little creep data are available on these materials (1-17). A number of block copolymers are now commercially available as thermoplastic elastomers to replace crosslinked rubber formulations and other plastics (16). For applications in which the finished object must bear loads for extended periods of time, it is important to know how these new materials compare with conventional crosslinked rubbers and more rigid plastics in dimensional stability or creep behavior. The creep of five commercial block polymers was measured as a function of temperature and molding conditions. Four of the polymers had crystalline hard blocks, and one had a glassy polystyrene hard block. The soft blocks were various kinds of elastomeric materials. The creep of the block polymers was also compared with that of a normal, crosslinked natural rubber and crystalline poly(tetra-methylene terephthalate) (PTMT). 

Wisch, C., and Meinecke, E., The static and DM properties of tilled elastomers with respect to C black loading and the stress-strain behavior of the unfilled matrix. ACS Rubber Div., Cleveland, OH, 10,95. Paper 109. 

Having examined the thermodynamic approach, we can now outline briefly the stress-strain behavior of an elastomer in terms of the chain conformations. 

In tensile tests of elastomers, the stress-strain behavior between successive load application cycles deviates from the first cycle (post prestressing). 

Fig. 5.(a). Stress-strain behavior of polyether polyurethaneurea elastomers (strain rate = 1.2%/sec.)-... 

Continum mechanics is also used to account for the observed stress-strain behavior exhibited by elastomers The most general form of the strain energy function (which vanishes at zero strain) is the power series... 

The stress-strain behavior of uncured EP copolymers with highly stereo- and regioregular propylene placements resembles that of natural rubber. Both elastomers possess all the requisites discussed in Section 12.10. In particular, they have negligible crystallinity at rest and are able to develop crystallinity under stretching. 

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