5.1 This test method covers one procedure for determining fatigue life at various extension-ratios. The strain cycle is characteristic of the type of test apparatus specified. Experience in fatigue testing shows that fatigue life may have a wide, non-normal distribution and, therefore, a large standard deviation that is compound dependent. Natural rubber, for example, has shown a narrower distribution than many synthetic rubbers. A large number of specimens may, therefore, be required to yield the desired precision. Comparison of different rubber compounds should be made with due consideration to the standard deviation for each (see 7.1).

5.2 Fatigue data, as generated in this test method, give primarily an estimate of the crack initation behavior of a rubber vulcanizate and only a very approximate measure of the crack propagation rate. The information obtained may be useful in predicting the flex-life performance of a compound in active service; however, the user should be aware that in actual use, products are subjected to many other fatigue factors not measured in this test method.

1.1 This test method covers the determination of fatigue life of rubber compounds undergoing a tensile-strain cycle. During part of the cycle, the strain is relaxed to a zero value. The specimens are tested without intentionally initiated flaws, cuts, or cracks. Failure is indicated by a complete rupture of the test specimen.

1.2 No exact correlation between these test results and service is given or implied. This is due to the varied nature of service conditions. These test procedures do yield data that can be used for the comparative evaluation of rubber compounds for their ability to resist (dynamic) extension cycling fatigue.

1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.