ASTM D6147 is a test method for determining the force decay (stress relaxation) in vulcanized rubber and thermoplastic elastomers in compression. The ASTM D6147 standard (Standard Test Method for Vulcanized Rubber and Thermoplastic Elastomer-Determination of Force Decay (Stress Relaxation) in Compression) was developed from testing in air and liquids, and this concept is important for rubber products such as seals and gaskets. This test defines two procedures (A and B) for determining the decrease in counterforce of a test specimen of vulcanized rubber or thermoplastic elastomer.
ASTM D6147 Determination of Force Decay in Vulcanized Rubber and Thermoplastic Elastomer in Compression
What is ASTM D6147?
ASTM D6147 Sample Preparation Guide
A cylindrical disc of diameter 13.0 ± 0.5 mm and a thickness of 6.3± 0.3 mm is used as a test specimen for the ASTM D6147 test procedure.
What are the Test Procedure and Requirements of ASTM D6147?
According to ASTM D6147, there are two test procedures:
- Method A
The test specimen is compressed at the test temperature and kept there for the duration of the test, with all force measurements taking place at that temperature.
- Method B
At 23± 2°C, the test specimen is compressed, and the initial counterforce measurement is taken. The test specimen is then stored in a chamber that is kept at the test temperature, but it is removed from the chamber for each of the subsequent force measurements, which are also taken at 23± 2°C.
The two ways of measuring force decay, A and B, do not produce the same results; hence, comparing the results from the two approaches should be avoided. The method chosen between A and B is dependent on the test’s purpose. Method A may be favored for foundational investigations and applications where sealing at elevated temperatures is a concern, whereas method B may be preferred for applications where temperature cycling from normal to elevated temperatures is an issue.
Analysis Result and Interpretation
ASTM D6147 is a test method for determining the force decay (stress relaxation) in vulcanized rubber and thermoplastic elastomers in compression.
As per ASTM D6147, the compression force decay (stress relaxation), R(t), after a specified duration of the test, t, expressed as a percentage of the initial counterforce, is calculated by:
where:
Fo = initial counterforce measured 30 min. after compression of the test specimen
Ft = counterforce measured after the specified duration of the test
Updated on August 8, 2026
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