Elastomers failure properties

Eqs. (8) and (11) are important because they predict a direct relationship between a failure property and network structure. If the Equations hold, then the following experimental results would be expected (1) l o for a series of networks of the same chemical composition will reflect only differences in crosslinking, and (2) 2 /n for chemically different networks of the same will reflect the differences in their backbone composition. Experiments such as these have been performed on a variety of elastomers e.g., polyurethanes,... 

Tensile properties of composite propellants depend on the tensile properties of the matrix, concentration of the components, particle size, particle-size distribution, particle shape, quality of the interface between fillers and polymeric binder, and, obviously, experimental conditions (strain rate, temperature, and environmental pressure). Many authors (2, 3) have explained the effect of fillers on the mechanical properties of composites, the importance of the filler-matrix interface on physical properties, and the mechanism of reinforcement of the material. Other efforts have examined the effect of experimental conditions on the failure properties of filled elastomers. Landel and... 

It is well known that elastomers, like virtually all solid materials, have preexisting, naturally occurring flaws (Roland and Smith, 1985). By intensifying local stresses, such flaws exert an influence on the failure properties of elastomers. More recently, interest in these flaws has increased, due to concerns about their potential for reducing the barrier performance of rubber films. This performance is crucial in the use of latex rubber products, such as surgical... 

Although elastomers are usually amorphous, strain-induced crystallization occurs in rubbers such as cA-l,4-polybutadiene, butyl rubber, and NR. Crystallization under stress, discovered 200 years ago [239], increases the modulus and most failure properties of rubber and is essential to performance in many... 

In some cases, double networks have shown increases in orientability and strain-induced crystallization, as well as improved fatigue resis-tance. ° In fact, some results show that there maybe less of a compromise between failure properties in general and the modulus, which may be due in part to the decreased hysteresis observed for some of these elastomers. There have even been reports of improved thermal stabil-ity, although it is hard to visualize how this would occur. Finally, electrical resistivity is more sensitive to strain in carbon-black reinforced double networks. Better molecular understanding of these observations is being sought with, for example, extensive studies of residual strains and birefringence. ... 

Dry RubbGr. Because of its enhanced crystallizability, guayule rubber can exhibit superior failure properties in unfilled rubber compositions. As a double network, an elastomer cured a second time while in a deformed state guayule rubber exhibits substantially better fatigue resistance than deproteinized Hevea rubber (118). When compounded with carbon black, guayule rubber and Hevea rubber behave similarly (119). In tread and wire skim stocks, the compoimding and performance behavior of guayule rubber was comparable to that of Hevea rubber (Tables 7, 8) (120). 

Work carried out to identify how the performance of power transmission belts may be improved is described. An examination is made of which mechanical properties of the elastomer compound are of significance in determining belt performance, and to identify how the significant elastomer compound properties may be changed to improve belt performance. This work encompasses the examination of belt failure and modelling of belt operation to ensure that the current limits of belt performance are fully understood. It is concluded... 

Since most polymers, including elastomers, are immiscible with each other, their blends undergo phase separation with poor adhesion between the matrix and dispersed phase. The properties of such blends are often poorer than the individual components. At the same time, it is often desired to combine the process and performance characteristics of two or more polymers, to develop industrially useful products. This is accomplished by compatibilizing the blend, either by adding a third component, called compatibilizer, or by chemically or mechanically enhancing the interaction of the two-component polymers. The ultimate objective is to develop a morphology that will allow smooth stress transfer from one phase to the other and allow the product to resist failure under multiple stresses. In case of elastomer blends, compatibilization is especially useful to aid uniform distribution of fillers, curatives, and plasticizers to obtain a morphologically and mechanically sound product. Compatibilization of elastomeric blends is accomplished in two ways, mechanically and chemically. 

Smith,T.L., Frederick, . E. Ultimate tensile properties of elastomers. IV. Dependence of the failure envelope, maximum extensibility, and equilibrium stress-strain curve on network characteristics. J. Appl. Phys. 36,2996-3005 (1965). 

Relationships between microvoid heterogeneity and physical properties in crosslinked elastomers, poly-(isobutylene-/7-methylstyrene-p-bromomethylstyrene) (PIB-PMS/BrPMS) terpolymers, were identified by a 3D-NMR imaging study. Three-dimensional reconstruction of the sample images reveals that the voids are spherically shaped. The experimental results indicate that high microvoid density in cured elastomers leads to crack initiation and accelerated crack growth, thereby resulting in premature mechanism failure of the materials. 

---