Local measurement on oedometric compression tests: Time and temperature ageing effects on a fluorosilicone

Abstract

O-ring durability is a key issue for engineering structures that require sealing over a long service life. Rubber-like materials are used for this type of component because of the assumption of incompressibility, i.e. a high bulk modulus $K$. However, this assumption has been called into question in the literature, particularly for elastomers under high hydrostatic pressures. This work examines the compressibility of rubber-like materials, with a particular focus on fluorosilicone elastomers (FVMQ). A method of confined compression using a transparent crucible is presented which allows local measurement of the displacement field. This technique provides a better understanding of the analysis of oedometric compression data and a reliable way to determine the $K$ value. Furthermore, this approach allows following the evolution of $K$ over time with accelerated ageing. Three ageing temperatures – 200, 220 and 250 °C – were tested up to 34, 15 and 1 weeks, respectively. For the three ageing temperatures, the FVMQ results show a decrease in $K$ values with ageing. In particular, at 250 °C, a turning point was observed after 72 h of ageing. These results highlight the influence of ageing on the compressibility of the FVMQ and the presence of two different ageing mechanisms affecting the $K$ evolution.