Elastomer seals are unlike any other materials that design engineers confront. Metal or plastic parts, for instance, are probably failing if visibly distorted. Seals deform into leak paths to function properly. In most applications, o-rings are installed with preset squeeze and stretch as correct design intent.
A dynamic seal application is best described as one where there is motion between a hardware component and the sealing element. Let's walk through everything you need to know about dynamic seals.