BS EN ISO 1421:2016 pdf download – Rubber- or plastics-coated fabrics — Determination of tensile strength and elongation at break Principle A test piece is extended at a constant rate of extension until it breaks. For method 1 (clause 7), the maximum force and the elongation at maximum force and, if required, the force at break and the elongation at break are determined. For method 2 (clause 8), the maximum force only is determined. 5 Apparatus 5.1 Constant rate of extension (CRE) tensile testing machine, having the following general characteristics: The machine shall be provided with means for reading and recording both the force applied to the test piece in stretching it to the breaking point and the corresponding extension of the test piece. It shall be provided with a strength indicator having several scales in order to ensure that the rupture of each test piece is obtained with a strength of 15 % to 85 % of the maximum of the scale used. Under conditions of use, the accuracy of the apparatus shall be class 1 as defined in ISO 7500-1. The error of the indicated or recorded maximum force at any point in the range in which the machine is used shall not exceed ± 1 %, and the error of the indicated or recorded jaw separation shall not exceed 1 mm. After the first 2 s of the test, the rate of increase in the distance between the clamps shall be uniform to within 5 %. If the force and elongation are recorded by means of data acquisition boards and software, the frequency of data collection shall be at least 8 s –1 . 5.2 Clamping device, with the central point of the two jaws of the machine in the line of pull, the front edges at right angles to the line of pull and their clamping faces in the same plane. The jaws shall be capable of holding the test piece without allowing it to slip. They shall be designed so that they do not damage the test piece or reduce its strength. Smooth, flat or engraved corrugated jaws can be used for clamping. Using suitable packing materials in the jaws, e.g. paper, leather, plastics or rubber, avoids difficulties in clamping in many cases. When tests are carried out and the test pieces either break at the jaws or tend to slip, the results may often...
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