In application where rubber seals are used, we encounter relaxation of stress in the material. That can cause inadequate sealing propereties in such systems. In this study, we want to determine long term changes of stress in silicone rubber.
With the use of a rotational rheometer, we exposed prepared samples of silicone rubber to a constant shear strain and measured the decrease of shear stress in time. The tests were performed at different temperatures in a short time period. The experimental results were used to calculate the values of relaxation moduli, which were transformed into data used for displaying the changes of stress relaxation in a longer time period by using time-temperature superposition. Analysis of shear relaxation shows, that the value of the relaxation modulus changed by 30 % in a 10-year period. The results therefore suggest that time dependent mechanical propereties have to be considered when using silicon rubber for sealing applications.