A large long-term accelerated test programme for elastomers (rubbery materials) is reported. In the programme the effects, on a range of physical properties, of accelerated ageing in a variety of environments for periods up to five years were studied for 48 thermoset rubbery materials and 27 thermoplastic materials. Example results for thermoset rubbery materials are given here.
The main focus is on thermo-oxidative ageing although the, sometimes very significant, effects of other factors is also considered. Key findings include the following [(a)-(c)].(a)
The wide validity of the (log time to failure against reciprocal absolute temperature) Arrhenius extrapolation method is confirmed.(b)
The results re-emphasise the importance of carefully specifying ageing conditions (e.g. which fluids there will be exposure to). The suitability ranking of two different elastomeric materials is often reversed if the conditions are changed.(c)
Ageing causes some measures of material properties to decrease more rapidly than others – indeed, some increase rather than decrease. Moreover, the slopes of the Arrhenius plots for (values of) different material properties can differ markedly. Selection of failure criteria is therefore crucial for lifespan prediction; thus it needs to be known which physical properties are important and what range of values of those properties is acceptable for a given application.