Strength of Elastomers

Fracture is a highly selective process only a small number of those molecules making up a test piece or a component actually undergo rupture the great majority are not affected. For example, of the 10 chain molecules per cubic meter in a typical elastomer, only those crossing the fracture plane, about 10 /m, will definitely be broken. Moreover, these will not all break simultaneously but successively as the fracture propagates across the specimen at a finite speed. 

the first questions posed in studying the strength of elastomers (and other materials as well) are where and under what conditions does fracture begin Also, what laws govern the growth of a crack once it has been initiated This chapter seeks to answer such questions, first in a general way and then with particular reference to important modes of failure of elastomers in service. It does not deal with the rather complex problem of the strength of composite structures, such as a pneumatic tire, which involves failure of adhesive bonds at interfaces between the components as well as fracture of the components themselves. 

We consider first the initiation of fracture from crack precursors. These are features of the material s microscopic structure that magnify applied stresses. The rate of development of cracks after initiation is treated next. Naturally, this depends on the local stress levels but also on the way in which these stresses vary with time. For example, rapid crack growth may take place if stresses are applied and removed frequently, whereas the crack may grow quite slowly, if at all, when the same stresses are held constant and never removed. This phenomenon of accelerated growth under dynamic stressing is termed mechanical fatigue or dynamic crack growth. It is treated in Sections 10.4.5 and 10.6. 

The Science and Technology of Rubber. http //dx.dol.Org/10.101S/B978-0-12-394584-6.00010-8 2013 Elsevier Inc. All rights reserved 

Because rubber is viscoelastic, or more generally anelastic, to varying extents and because the mechanical properties depend on rate of deformation and temperature, it is not surprising to find that the strength is also dependent on the rate at which stresses are applied and on the temperature of measurement. These effects are discussed in Sections 10.4.2 and 10.5.1. Other effects of the environment, notably the destructive action of ozone, are discussed in Section 10.8. Finally, a brief survey is given of abrasive wear. 

---

The two systems discussed above demonstrate two mechanisms whereby the tensile strength of elastomers can be reinforced by the presence of rigid fillers. For the polymeric fillers dispersed within a vulcani-zate, the filler operates by raising the viscosity of the matrix, analogous to a decrease in temperature, but without affecting the dynamic, high frequency response (there is ample experimental evidence of the independence of Ty on presence of filler). There is also some indication that the rigidity of the filler affects the extent of reinforcement. 

Part 1 Trouser, angle, and crescent test pieces Part 2 Small (delft) test pieces Standard test method for tear strength of conventional vulcanized rubber and thermoplastic elastomers Testing of rubber and elastomers Determination of the tear strength of elastomers Trouser test piece... 

Volume Swell and Tensile Strength of Elastomers After Exposure to Ethanol, Indolene HO-III,... 

Volume Swell and Tensile Strength of Elastomers After Exposure to Methyl t- Butyl Ether (MTBE), Indolene HO-III, Spiked Indolene HO-III, and lOZ MTBE mixtures with Each of the Indolenes... 

FIGURE 8.2 Tear strength of elastomers. (From Tomanek, A. Silicones and Industry, Wacker-Chemie GmBH, Munich, 1984. With permission.)... 

Table I-V shows the compounding receipt of the samples used in this study.In th etable phr means pers per hundred resin (rubber). The thickness of the samples was about 0.5 mm. EPDM-3, 4, 5, 6 and 7 are the series of the compounding formula of the curing by low sulfur. EPDM-2 contains the relatively higher sulfur with Hypalon (Chlorosulphonated polyethylene) that increases tensile strength of elastomer. EPDM-1, 8 and 10 were crosslinked by peroxide. Triallyl isocyanurate in EPDM-1 is a multi-functional compound that increases the concentration of network.

---