Compression Stress Relaxation Database

The Compression Stress Relaxation (CSR) Database provides insight into how a material will perform over time. It can be used to estimate the life of a part and its ability to meet a specification at some point in the future. CSR data are of paramount importance in sealing applications.

Why the database is used
Engineering calculations and Finite Element Analysis (FEA) provide the engineer an idea of what the application looks like instantaneously. Predictions of initial performance are not valid over time and stress relaxation effects must be considered. This allows the designer to get an idea how well the design will perform over the life of the application.

When to use the database
This database should be used when performance over time predictions are required in the design. Typically, stress relaxation will relate to pressure or force specifications.

How to use the database
The database is used to extrapolate performance from initial conditions to a desired time. Initial conditions are determined via calculation, FEA or experiment. Using the Initial Force Fo, initial time to=0.5 hrs, and the “A” and “B” values from the data sheets for a given grade, a calculation using the formula on the data sheet can be made to determine the residual force after stress relaxation effects at any desired time.

Testing of materials is performed according to ISO 3384 A or B. The difference between the two tests is that ISO 3384 A records data at the aging temperature while ISO 3384 B cools samples to room temperature for data, regardless of the aging temperature.

Our Design Team of engineers is proud to offer this data from our Santoprene™ TPV product line. Please contact the AnswerPerson for these available documents.

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An example of how this process works is shown below:

A compression seal made out Santoprene TPV 201-64 is designed such that it is compressed 25% at room temperature. Experiments (or calculations or FEA) show the initial sealing force (Fo) is 500 N. Of interest is what the sealing force is after 5 years.

Using the formula on the data sheet: [F(t) / Fo] x 100 = A – B x log (t/to)

The CSR data sheet for 201-64 shows the “A” and “B” values to be 97.5 and 7.7, respectively. The time of interest, t, is 5 years, or 43800 hours. The initial time, to, is 0.5 hours. This becomes:

[F(t) / 500] x 100 = 97.5 – 7.7 log (43800/0.5)
And F(t) is calculated to be 297 N. This means the sealing force of the part is 297 N after 5 years of service life.

A sample CSR data sheet for 201-64 can be requested from the AnswerPerson.