Viscoelastic Behavior of Rubbery Materials

Abstract

Contents* Early molecular theories of rubber hyperelasticity were called kinetic theories, in correspondence to the behavior of ideal gases (the molecules of which have neither size nor mutual interactions). The elastic forces of an ideal rubber are caused by thermal motion of the network chains attempting to restore the higher entropy, isotropic state; thus, analogous to ideal gases, ideal rubber elasticity is a statistical effect. In real materials there is also an energy contribution (negative or positive) due to the difference in energy between trans and gauche conformations of the repeat units.of alternative networks -interpenetrating, double, bimodal, heterogeneous, and deswollenare discussed at the conclusion of the chapter.

Thermodynamic scaling of vibrational dynamics and relaxation

“…16 [73], so that we cannot extend Eq.17 to τ ee . The coincidence of the scaling exponent for the segment relaxation and the chain reorientation has been noted in poly(propylene glycol), 1,4-polyisoprene as well as in poly(oxybutylene) [114,115]. Nonetheless, Fragiadakis et al, investigating very carefully the Table II. density scaling in 1,4-Polyisoprene (PI) of different molecular weight by dielectric relaxation, noted that there is a small difference in the exponent γ ts for the segmental and the chain modes of the lowest molecular weight PI with degree of polymerization 18 [116].…”

Elastomer-metal laminate armor

“…The agreement is qualitatively satisfactory, although it is not quantitative. The deviations arise due to a number of factors, including non-constant strain rate during the Hopkinson bar measurements, the known limitations of the Ogden model, and the approximation entailed in assuming decoupling of strain and rate effects [51]. Nevertheless, the modeling confirms that the SHPB measurements capture the key aspects of wave transmission through the polymer coating and the laminate, with the caveat that extension of these results to ballistic performance is limited due to the difference in strain rates.…”

Strength Enhancement From Heterogeneous Networks of Ethylene–propylene/Ethylene–propylene–diene

“…21,22 At very low degrees of cross-linking, a network lacks mechanical integrity, while high levels of cross-links cause embrittlement. This maximum is observed just past the gel point, so that for commercial elastomers, as well as the materials reported on herein, increasing cross-link density leads to lower strength.…”