Elastomers, strength tensile rupture

In the case of siloxane elastomers, the testing of mechanical properties is of particular importance. Elongation or tensile measurements are used almost to the exclusion of other types of mechanical tests, probably because of their simplicity. In this way, structural information is obtained about the networks, such as their degrees of cross-linking.92 Measurements of the ultimate strength (modulus at rupture), and the maximum... 

TBP corrrpletely ruptures hard block domains of rrrethane urea re rdless of their initial concerrtration of elastomer. Orrly SPU chemical network resists swelling by TBP. The eqrrilibrirrm swelling of SPU in DBP decreases with increase in concerrtration of hard blocks. As a result tensile strength of a material is decreased to a lesser degree. The lowest decrease in terrsile strength is observed in SPU-1 swollen to equilibrium in DBP. SPU-1 has 37% hard blocks (Figirre 10.80). 

Tension testing of a vulcanized elastomer also permits the determination of the tensile strength, which is the maximiun stress applied during stretching a specimen to rupture the corresponding rupture strain is called the maximum extensibility (49-52). Typical values are given in Table 1 (14). Dumbbell and ring specimens can be used. 

This envelope may be used to describe relaxation, creep or constant strain rate measurements. A change in strain rate or temperature only shifts a point along the failure envelope, which is thus dependent only on the structural characteristics of the elastomer. The ultimate properties of rubbers are mainly governed by their viscoelastic properties, and reduced master curves can be obtained for tensile strength and strain as a function of time to break. The failure process is a non-equilibrium one, developing with time and involving the consecutive rupture of the molecular chains. The ultimate properties can then be predicted from creep measurements. ... 

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