1) Developments in Stress Relaxation and Lifetime estimation test methods and instruments 2) Developments in low temperature testing and instruments
1) Developments in Stress Relaxation and Lifetime estimation test methods and instruments Stress relaxation tests are becoming more and more popular for determination of rubber properties. From the beginning stress relaxation tests were used mainly in scientific projects at universities, but a growing use has been shown in recent years and this may be caused by the introduction of stress relaxation tests in product standards, such as sealing rings for pipes. The automotive industry has also started to specify stress relaxation tests for critical sealing products in the cars. The latest requirements from the automotive industry is temperature cycling tests from subzero to elevated temperatures. This paper will describe the test methods, the instruments, test results and how to use the test data for lifetime estimations. 2) Developments in low temperature testing and instruments The low temperature properties of rubber materials are important in colder climates, such as that encountered in Scandinavia. The requirements for these properties have since long been included in specifications, especially those of the automotive industry. There are a number of test methods in use, the most common methods in Scandinavia is the Temperature Retraction Procedure, also known as the TR-test. This test is now also included in the new material specifications that have been developed by the Swedish Standards Institute. Another low temperature test is the Gehman test which measures the stiffness (modulus) at a range of temperatures. A problem with both these methods is that they are both very time consuming to perform however this is eliminated with automated instruments. This paper will describe what happens in the rubber material at low temperatures and review the most common standardized test methods for low temperature properties. The new automated instruments used for testing and the improved precision that can be achieved will also be discussed.