Rubber fatigue failure

Since fatigue failure of rubber is envisioned as growth of intrinsic flaws, measurement of fatigue lifetimes (e.g., deformation cycles to failure) can provide a measure of the intrinsic flaw size (Gent et al., 1964 Lake andLindley, 1965 Lake, 1983). Table 3.4 includes the flaw sizes determined from the fatigue life of these sample NR compounds (Choi and Roland, 1996). 

Rubber failure upon application of stress is delayed by i) viscoelastic energy dissipation and il) crystallization upon strain of the base polymer. A peculiar rubber failure, namely fatigue failure, is also affected by the same factors. The presence of carbon black or other reinforcing agents does not diminish the contribution of the base polymer on fatigue resistance. 

There have been a number of Japanese papers on fatigue failure of rubber products but translations have not been found in most cases other than a wide ranging review (100) and a study on failure of timing belts (156). 

A discussion is presented of the mechanisms involved in fatigue phenomena of rubber rolls, and of the determination of the causes and sites of fatigue failure. 8 refs. Articles from this journal can be requested for translation by subscribers to the Rapra produced International Polymer Science and Technology. 

CUMULATIVE DAMAGE AND FATIGUE FAILURE CRITERIA OF CORD-RUBBER COMPOSITES... 

Vibration is a major destmctive force in many types of machinery. Vibration can lead to wear and fatigue failure of rigid materials like alloys and plastic components. The helicopter benefits from the unique flexibility and vibration dampening characteristics of elastomeric adhesives. Elastomers are used to transfer torque to the rotor blades while providing flexibility and vibration control. Rubber tires are another example of elastomeric adhesive use. Consumers have enjoyed a steady increase in the useful life expectancy of rubber tires due to improvements in adhesion between the elastomer, tire cords, and the filler. The rubber tire industry has driven a great deal of the fundamental research on elastomeric materials in engineering design. 

Children s toys are especially prone to fatigue failure, not only because children subject them to seemingly endless hours of use but also because the toys are generally not overdesigned. Building a toy too rugged could make it too heavy for the child to manipulate, not to mention more expensive than its imitators. Thus, the seams of rubber balls crack open after so many bounces, the joints of metal tricycles break after so many trips around the block, and the heads of plastic dolls separate after so many nods of agreement. 

Due to their good damping properties, soybean oil polymers may also find applications in places where the reduction of noise and prevention of vibration fatigue failure is required (39). Several conventional polymers, such as polyacrylates, polyurethanes, polyvinyl acetate, as well as natural, silicone and SBR rubbers, which are currently used as damping materials, might be replaced by soybean oil polymers. Unlike the above-mentioned thermoplastics, soybean oil polymers are capable of efficient damping over wider temperature and frequency ranges (23). 

What is certain is that the initiation and propagation of a tear is a real and very important factor in the failure of rubber products, being involved in fatigue and abrasion processes as well as the catastrophic growth of a cut on the application of a stress. There is, therefore, considerable interest in the tearing resistance of rubbers. What is uncertain is how tear resistance should be measured and the results interpreted. 

With very good bonding systems, it is often difficult to discriminate between the systems because of failure in the rubber and yet in service differences in performance may be evident. This situation was recognised by Buist et al8,24 who made comparisons of various methods and observed that, in service, bonds may be subjected to impacts (i.e. high strain rates) or to repeated dynamic cycling (fatigue). Neither of these factors is considered in the standard methods discussed above. 

In Figure 2 we can observe the variations of tensile strain versus number of cycle for failure. As it can be seen, waste tire reinforeement ean decrease the tensile strain in contrast to non- reinforced sample. In certain bitumen percent, the tensile strain in reinforced sample is less than the tensile strain in non- reinforced specimen. It can be seen that the number of cycle for failure in reinforced sample is more than non - reinforeed sample. Therefore, the reduction in fatigue cracks in reinforced specimen is expected. In samples with 5 and 6 percents of bitumen, the number of cycles for failure is increased signifieantly. It should be noted that with 5 percent of bitumen the application of waste rubber ean cause a better cohesion between aggregates and bitumen. While using 4% bitumen the difference between tensile strain in reinforced specimen and non- reinforced sample is poor. This is because of percent reduction in the bitumen quantity. However, for 5 percent bitumen this difference is noticeable. Although the bitumen percent used is not optimum, therefore, the waste rubber reinforcement, lead to the decrease in tensile strain in contrast to non - reinforced sample. The result has shown in Figure 2. 

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