ASTM D6147: Rubber TPE Compression Force Decay Testing Services

What Is ASTM D6147 Rubber TPE Compression Force Decay?

Squeeze an O-ring into place and leave it there for a few years, and the real question isn’t how much it compressed going in – it’s how much sealing force it still has left. ASTM D6147, Standard Test Method for Vulcanized Rubber and Thermoplastic Elastomer-Determination of Force Decay (Stress Relaxation) in Compression, was written to answer exactly that. Instead of measuring deflection under a set load, the standard tracks how the counterforce a compressed rubber or TPE specimen pushes back changes over time while its deformation stays fixed. That’s an important distinction: a seal can hold its shape perfectly while quietly losing the force it needs to keep a joint tight, and D6147 is built to catch that before it becomes a field failure.

Here’s how it works in practice. A specimen gets compressed to a fixed deformation between parallel plates, then monitored – either continuously through an instrumented load cell or at set intervals – while it sits in air or immersed in a test fluid at a controlled temperature. The resulting force-versus-time curve reveals two things happening at once: a fast, largely physical relaxation that dominates early on, and a slower, chemistry-driven relaxation – oxidation, further crosslinking, degradation – that takes over as exposure continues. Because these two mechanisms behave so differently, the standard specifically warns against extrapolating short-term data into long-term predictions, or treating a quick high-temperature run as a stand-in for real-use conditions.

For engineers designing seals, gaskets, and O-rings that need to stay tight for years in demanding environments, this data is immediately useful. It tells them how much sealing margin is left, and roughly when a compound will need replacing, well before a leak ever shows up in the field.