ABSTRACT
This chapter focuses on polymers that exhibit elastomeric properties, since these are the most valuable in seals and illustrates the key concepts affecting polymer seal behaviour. Polymeric materials play a crucial role in fluid sealing. Many types of seal are made largely or entirely of such materials, while others have at least some key components of polymeric material. Polymeric material is a term used to cover both elastomeric and plastic materials. Elastomeric materials are especially important in fluid sealing because they have certain uniquely valuable physical properties. Many practical limitations of engineering elastomers as seal materials arise from degradation processes brought about by direct or indirect chemical effects: chemical degradation and thermal degradation. Poisson ratio of real elastomers is typically about 0.4995 for small strain; the actual value depends on details of the compounding and manufacture. The fact that this value is so close to 0.5 can cause problems when finite element software is used to model elastomer seal behavior.
