Elastomer pure shear

If an elastomer sample in the form of a unit cube is deformed by pure shear, then the three principal extension ratios are A, = X, = 1, X = MX. [Compare with the case of simple extension where X = X = 1 NX.] Following the arguments of Section B, derive an expression relating aE and A, where [Pg.208]

Only a very few studies have been carried out to characterize the reinforcement of in situ precipitated silica in elastomers in shear [3,69,72,73]. There are two types of shear simple shear and pure shear. Simple shear is a type of strain obtained by sliding a plane which is parallel to a given plane, through a distance which is proportional to the distance from the given plane [3,69]. The lateral faces of a... 

In shear measurements, bimodal PDMS networks showed large upturns in the pure-shear modulus at high strains, similar to those reported for elongation and biaxial extension. Tear tests were carried out on bimodal PDMS elastomers, using the standard trouser-leg method. Tear... 

Fig. 5.58 Pure shear test piece used in the study of the tearing of elastomers, (a) Specimen before crack propagation (b) after crack propagation. (After Andrews, Chapter 9, in Polymer Science, ed. Jenkins, North-Holland, 1972.)...

Unlike shear viscosity, extensional viscosity has no meaning unless the type of deformation is specified. The three types of extensional viscosity identified aind measured are uniaxial or simple, biaxial, and pure shear. Uniaxial viscosity is the only one used to characterize fluids. It has been employed mainly in the study of polymer melts, but also for other fluids. For a Newtonian fluid, the uniaxial extensional viscosity is three times the shear viscosity ( fe)uni = 3/ . This is confirmed at very low shear rates in Figure 13, which provides a typical example of the extensional viscosity behavior of a polymer (129). The two other extensional viscosities are used to study elastomers in the form of films or sheets. Uniaxial and biaxial extensions are important in industry (118,125-128,130,132), the former for the spinning of textile fibers and roller spattering of paints, and the latter for blow molding, vacuum forming, film blowing, and foam processes. 

From the value of the SAN Mff), it is possible to calculate the Mej of the different blends by Equation 15. At an elastomer phase content of 40%, Mej was equal to 10,000. As we have stated above, extrudate expansion of the pure elastomer phase was negligible. At higher graft contents, the relation between shear modulus and elastomer phase content probably could change. It is there-... 

Much of the knowledge in this area is either derived from practical experience or anecdotal. Theoretical predictions of the viscosity of elastomer blends [46f, g] are of limited use since (1) the inhomogeneous phase morphology of an elastomer blend changes easily in response to applied stress, and (2) the nonuniform distribution of fillers and plasticizers in the phases responds to flow. These structural changes in elastomer blends under shear lead to anomalous rheological properties quite different from the expected average of pure components. 

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