ASTM-D624:2020 pdf free download – Standard Test Method for Tear Strength of Conventional Vulcanized Rubber and Thermoplastic Elastomers.
7.7.1 Tear testing is inherently a highly variable measurement since it has many characteristics similar to fatigue testing and is known to give widely dispersed test results, frequently with a non-normal distribution. For referee tear testing, a minimum of five test pieces is recommended.
7.8 Measure the thickness of each test piece.
7.8.1 For Type A, B, and C test pieces, measure the thickness at three places across the width, near the center, using a micrometer conforming to Practice D3767. One of the measurements should be at the slit or apex. Record the median value for calculation of test results.
7.8.2 For Type T test pieces, measure the thickness at three places across the length and record the median value.
7.8.3 For Type CP test pieces. the thickness of the tear path may he measured one of two ways: (I) the total thickness of the test piece along the groove is measured at three places, averaged, and 3.60 mm is subtracted to account for the mold insert sections that form the groove; or (2) the torn surface is examined with a small binocular magnifier with a graduated reticle and the thickness measured and averaged. The second method is more accurate, hut the two methods have been found to agree to within about 5 %. For routine work the first method has been found to he satisfactory. Based Ofl the mold dimensions, the thickness is approximately between 1.70 and 1.80 mm.
8. Test Piece Conditioning
8.1 Cut surfaces of vulcanized rubber undergo a change over a period of time that may affect the initiation of tearing. Therefore, it is important that the conditioning intervals after using cutting dies, nicking devices, razor blades or knives be followed. Deviation from these intervals may affect the test results.
8.2 Test pieces shall be protected from exposure to light during the interval from vulcanization to testing.
8.3 The minimum time between vulcanization and testing shall he 16 h.
8.4 Test pieces shall be conditioned at a standard laboratory temperature of 23 ± 2°C as defined in Practice D 1349 for a minimum of 3 h before nicking or cutting. If the material is affected by moisture, the relative humidity shall he maintained at 50 ± 5 % and the specimen shall be conditioned for 24 h prior to testing.
8.5 Test pieces may be nicked or cut and tested immediately after conditioning but the maximum time between nicking or cutting and testing shall be 24 h.
8.6 If test piece preparation involves buffing, the interval between bulling and testing shall not exceed 72 h. Nicking or cutting shall be performed after any aging treatment.
8.7 If the test is to be carried out at a temperature other than a standard laboratory (room) temperature. the test pieces shall be conditioned a the test temperature for a minimum time sufficient to reach temperature equilibrium prior to testing. This period should be kept as short as possible to avoid aging the test pieces.