BS ISO 3384-1:2011 pdf download – Rubber, vulcanized or thermoplastic — Determination of stress relaxation in compression Part 1 : Testing at constant temperature 4 Principle A test piece of vulcanized or thermoplastic rubber is compressed to a constant deformation and maintained at a predetermined test temperature. The decrease in counterforce is then measured. In method A, the compression is applied and all counterforce measurements are made at the test temperature. In method B, the compression is applied and all counterforce measurements are made at a standard laboratory temperature. The test pieces are stored at the test temperature. The test can be conducted in a gaseous or a liquid environment. The two methods, A and B, of carrying out the measurement do not give the same values of stress relaxation, and comparison of values obtained from the two methods should be avoided. The method selected for use depends on the purpose of the test. Thus, for fundamental studies and in applications where sealing at elevated temperatures is a problem, method A might be preferred, and in applications where temperature cycling from normal to an elevated temperature is a problem, method B might be preferred. NOTE Other methods can be used for specific purposes, such as applying the compression at standard laboratory temperature and making all counterforce measurements at a different temperature. 5 Apparatus 5.1 Compression device, consisting of two parallel, flat, highly polished plates made from chromium- plated or stainless steel or another corrosion-resistant material, between the faces of which the test pieces are compressed. Flatness, surface roughness, parallelism and rigidity of the plates are all important. The surfaces of the compression plates shall be ground and polished. Compression plates shall be flat and parallel and shall not undergo any distortion when the test load is applied. NOTE A finish to the surface giving a roughness profile Ra (see ISO 4287) of not worse than 0,4 µm has been found to be suitable. Such a roughness profile Ra can be obtained by grinding or polishing. When the apparatus is assembled without a test piece, the gap between the plates shall not vary by more than 0,01 mm. When the test assembly is subjected to the test load with a test piece between the plates, neither compression plate shall bend by more than 0,01 mm. The plates shall be of sufficient size to ensure that the whole of the compressed test...
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