ISO 37:2011 pdf free download – Rubber, vulcanized or thermoplastic一 Determination of tensile stress-strain properties.
11 Marking of dumb-bell test pieces
If using a non-contact extensometer, mark the dumb-bell test pieces with two reference marks to define the test length as specified in Table 1, using a suitable marker. The test piece shall be unstrained when it is marked.
The lines shall be marked on the narrow part of the test piece, as shown in Figure 2, i.e. equidistant from the centre of the test piece and at right angles to its longitudinal axis.
12 Measurement of test pieces
12.1 Dumb-bells
Measure the thickness at the centre and at each end of the test length with the thickness gauge. Use the median value of the three measurements to calculate the area of the cross-section. In any one dumb-bell, none of the three thickness measurements of the narrow portion shall differ by more than 2 % from the median thickness. The width of the test piece shall be taken as the distance between the cutting edges of the die in the narrow part, and this distance shall be measured in accordance with ISO 23529 to the nearest 0,05 mm. Test pieces cut from products might have a non-rectangular cross-section, in which case the width shall be measured directly on the test piece.
12.2 Rings
Measure the radial width and axial thickness at six approximately equally spaced positions around the ring. The median value of each set of measurements shall be used in calculating the area of the cross-section. The internal diameter shall be measured to the nearest 0,1 mm. Calculate the internal circumference and the mean circumference as follows:
Internal circumference = it x internal diameter
Mean circumference = it x (internal diameter + radial width)
12.3 Comparison of groups of test pieces
If two groups of test pieces (either dumb-bells or rings) are being compared, the median thickness for each
group shall be within 7,5 % of the grand median thickness for the two groups.
13 Procedure
13.1 Dumb-bell test pieces
Insert the test piece into the tensile-testing machine, ensuring that the end tabs are gripped symmetrically so that the tension is distributed uniformly over the cross-section. It is strongly recommended that the load cell be reset to zero before each test. If necessary, apply a prestress of 0,1 MPa so that the test piece is not bent when the initial test length (see Figure 2) is measured. If necessary, set up the extensometry device. Start the machine and monitor continuously the change in test length and force throughout the test to an accuracy of ± 2 % or as required for the purposes of Clause 15.
The nominal rate of traverse of the moving grip shall be 500 mm/mm for type 1, type 1A and type 2 test pieces and 200 mm/mm for type 3 and type 4 test pieces.
Any test piece that breaks outside the narrow portion or yields outside the test length shall be discarded and a repeat test conducted on an additional test piece.
NOTE In making visual measurements, care should be taken to avoid inaccuracies due to parallax.
B.1 General
The repeatability and reproducibility of the method were calculated on the basis of ISO/TR 9272:2005. Original data were treated for outliers at the 5 % and 2 % significance levels on the basis of the procedures described in ISO/TR 9272.
B.2 Details of test programmes
B.2.1 Two inter-laboratory test programmes (lTPs) were organized.
The first ITP in 2001 was as follows:
Three different compounds of NR, SBR and EPDM were used for tensile tests. A test result for this test method was the average or mean of five separate measurements of each of the properties as indicated below. A total of 23 laboratories in eight countries participated in the programme.
The second ITP in 2002 was as follows:
One NR compound was used for tensile testing. The compound formulation was the same as the NR compound used in the first ITP.
A total of 17 laboratories in six countries participated in the programme.
The fully prepared rubber test pieces were sent to each laboratory for evaluation in both ITPs, thus giving a type 1 precision.
B.2.2 The test properties to be measured were tensile strength at break (TSb), elongation at break (Eb), stress at 100 % elongation (S100) and stress at 200 % elongation (S200).
B.2.3 Three types of dumb-bell, type 1, type 2 and type 1A, were tested.
The type I was tested with two test lengths of 20 mm and 25 mm marked on them in the first ITP, but for the second ITP only test pieces with a test length of 25 mm were tested.