ISO 37:2017 download.Rubber vulcanized or thermoplastic-Determination of tensile stress-strain properties.
WARNING 1 — Persons using ISO 37 should be familiar with normal laboratory practice ISO 37 does not purport to address all of the safety problems, if any. associated with its use. It is the responsibility of the user to establish appropriate safety and health practices and to determine the applicability of any other restrictions.
WARNING 2—Certain procedures specified in ISO 37 might Involve the use or generation of substances, or the generation of waste, that could constitute a local environmental hazard. Reference should be made to appropriate documentation on sale handling and disposal after use.
1 Scope
ISO 37 specifies a method for the determination of the tensile stress-strain properties of vulcanized and thermoplastic rubbers.
The properties which can be determined are tensile strength, elongation at break, stress at a given elongation, elongation at a given stress, stress at yield and elongation at yield. The measurement of stress and strain at yield applies only to some thermoplastic rubbers and certain other compounds.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 5893, Rubber and plastics test equipment — Tensile, flexural and compression types (constant rate of traverse) — Specification
ISO 235292O16, Rubber — General procedures for preparing and conditioning test pieces for physical test methods
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedla: available at http://www.ulectrupedla.org)
— ISO Online browsing platform: available at httpJjwww.ko,orelobp
3.1
tensile stress
stress applied so as to extend the test piece
Note ito entry. It is calculated as the applied force per unit area ol the original cross-section of the test length.
3.2
elongation
E
tensile strain, expressed as a percentage of the test length. produced in the test piece by a tensile
stress (3.1)
3.3
tensile strength
TS
maximum tensile stress (3.]) recorded In extending the test piece to breaking point
Note ito entry: See Figure 1.
3.4
tensile strength at break TSb
tensile stress (31) recorded at the moment of rupture
Note I to entry: See Figurel.
Nose 2 to entry: The values of TS and TSb might be difterent if, after yield at the ek,najaUon (3) continues and is accompanied by a drop in stress, resulting in TSb being lower than TS Isec Fgurc1 c)J.
3.5
elongation at break
Lb
tensile strain In the test length at breaking point
Note I to entry: See Figure L
3.6
elongatton at a given stress
tensile strain in the test length when the test piece is subjected to a given tensile stress (31)
3.7
stress at a given elongation
SQ
tensile stress (3J) in the test length required to produce a given elonput ion (12)
Note 1 to entry In the rubber industry, this definition is widely identified with the term modulus and care should be taken to avoid confusion with the other use of modulus to denote the slope otthe stress-strain curve at a given elongation
3.8
tensile stress at yield
Sy
tensile stress (31) at the first point on the stress-strain curve where some further increase in strain
occurs without any increase In stress
Note 1 to entry This might correspond either to a point of inflection scr FIgure 1 b)J or to a maximum Isee EIgux1 c)J.
3.9
elongation at yield
Ey
tensile strain at the first point on the stress-strain curve where some further increase in strain is not
accompanied by an increase in stressNote Ito entry: See Figure1.
3.10
test length of a dumb-bell
initial distance between reference points within the length of the narrow portion of a dumb-bell test piece used to measure elongation (12)
Note 1 to entry: See Figure 2,
4 Principle
Standard test pieces, either dumb-bells or rings, are stretched in a tensile-testing machine at a constant rate of traverse of the driven grip or pulley. Readings of force and elangation are taken as required during the uninterrupted stretching of the test piece and when it breaks.
5 General
Dumb-bell and ring test pieces do not necessarily give the same values for their respective stress-strain properties. This Is mainly because In stretched rings, the stress is not uniform over the cross-sectlo,t A second factor is in the existence of grain which might cause dumb-bells to give different values depending on whether their length is parallel or at right angles to the grain.
The main points to be noted in choosing between rings and dumb-bells are as follows.
a) Tensile strength
Dumb-bells are preferable for determination of tensile strength. Rings give lower, sometimes much lower, values than dumb-belLs.
b) Elongation at break
Rings give approximately the same values as dumb-bells, provided that
1) the elongation of rings is calculated as a percentage of the initial internal circumference, and
2) dumb-belLs are cut at right angles to the gram if this is present to a significant degree.
Dumb-bells shall be used if it is required to study grain elfects, as rings are not suitable (or this purpose.
c) Elongation at a given stress and stress at a given elongation
The larger dumb-bells (types 1,2 and IA) are generally preferred.
Rings and dumb-bells give approximately the same values provided that
1) the elongation of rings is calculated as a percentage of the Initial mean circumference, and
2) the average value Is taken for dumb-bells cut parallel and at right angles to the grain II this is present to a significant degree.
Rings might be preferred In automated testing, due to the ease of handling of the test pieces, and in the determination of stress at a given strain.
6 Test pieces
6.1 General
Miniature test pieces might give somewhat dilterent, usually higher, values for tensile strength and elongation at break than the larger test pieces.
Seven types of test piece are provided, I.e. dumb-bell-shaped types 1. 2. 3, 4 and 1A and ring-shaped types A (normal) and B (miniature). The results obtained for a given material are likely to vary according to the type of test piece used. Therefore, the results obtained for different materials should not be regarded as comparable unless the same type of test piece has been used.
When preparation of test pieces requires buffing or thickness adjustment, results might be affected.
6.2 Dumb-bells
Dumb-bell test pieces shall have the outline shown in Figure 2.
I test length (see tthl±1)
FIgure 2— Shape of dumb-bell test pieces
The standard thickness o(the narrow portion shall be 2,0mm * 0.2 mm for types 1,2.3 and IA and 1,0mm ±0.1 mm for type 4.
The test length shall be In accordance with Table 1.
The other dimensions olthe dumb-bells shall be as produced by the appropriate die (see Table 2)..
For non-standard test pieces, e.g. those taken from finished products, the maximum thickness of the narrow portion shall be 3.0mm for types I and IA, 2,5 mm for types 2 and 3, and 2.0mm for type 4.
Table I — Test length of dumb-bells
Tipe1A
1,pe2
Type3
20±O,Sd
20±0.5
1020,5
type of test piece Type I Type 4
Ted length (mm) 25 ± 0,5 1020.5
The text length xhull not exceed the length ol the narrow porINm olthr te3t piece (ihmenxion C In IahIc2J-
Type 3 and 4 dumb-bell test pieces shall only be used where insufficient material is available for the larger test pieces. These test pieces are particularly suitable for testing products and are used In certain product standards. e.g. type 3 dumb-bells have been used for testing pipe sealing rings and cable coverings
6.3 RIngs
The standard type A ring test piece shall have an internal diameter of 44,6 mm * 0.2 mm. The median axial thickness and median radial width shall be 4 mm ± 0,2 mm. The radial width of any ring shall nowhere deviate from the median by more than 0.2 mm and the axial thickness of the ring shall nowhere deviate from the median by more than 2 %.
The standard type B ring test piece shall have an Internal diameter of 8mm ±0,1 mm. The median axial thickness and median radial width shall be 1 mm ± 0,1 mm. The radial width of any ring shall nowhere deviate from the median by mare than 0,1 mm This test piece shall be used only where insufficient material is available for the larger type A test piece.
7 Apparatus
7.1 Dies and cutters
All dies and cutters used shall be in accordance with ISO 23529. Dies for preparation of dumb-bells shall have the dimensions given in Table 2 and Flgurc 3 except for the cutting edge for which Figure 3 only indicates a suitable geometry. The departure from parallelism at any point along the width of the narrow portion of the die shall nowhere exceed 0,05 mm.
For a method of cutting type H ring test pieces, see AnnexA.
Table 2— Dimensions oldies for dumb-bell test pieces
Dimension
A greater overall length might be necessary to ensure that only the wide end tabs cease into contact with the machine grips. thus avodlisg stwulder breaks.
7.2 Thickness gauge
The instrument for measuring the thickness of dumb-bell test pieces and the axial thickness of ring test pieces shall be in accordance with that used in method A of ISO 23529:2016.
The instrument for measuring the radial width of ring test pieces shall be similar to the above, except that the contact and base plate shall be shaped to fit the curvature of the ring.
7.3 Cone gauge
A calibrated cone gauge or other suitable equipment shall be used to measure the internal diameter of ring test pieces. The equipment shall be capable of measuring the diameter with an error of not more than 0,01 mm, The means of supporting the ring test piece to be measured shall be such as to avoid any significant change in the dimension being measured.
7.4 Tensile-testing machine
7.4.1 The tenslie-testing machine shall comply with the requirements of ISO 5893, having an accuracy of force measurement complying with class 1. An extensometer, where used, shall have an accuracy complying with dass I) for type I • IA and 2 dumb-bell test pieces and class E for type 3 and 4 dumb-bell test pieces. The machine shall, as a minimum, be capable of operating at rates of traverse of 100 mm/mm, 200 mm/mm and 500 mm/rn in.
When testing dumb-bells, the method of measuring the extension might require the test machine to apply a small prestress to the test piece to avoid it bending. In this case, the machine shall be capable of applying the necessary prestress.
7.4.2 For tests at temperatures other than a standard laboratory temperature, a suitable thermostatically controlled chamber shall be fitted to the tensile-testing machine. Guidance [or achieving elevated or subnormal temperatures Is given In ISO 23529,
7.5 Test rig for ring test pieces
An example of a test rig using pulleys for testing rings is shown In Figtue4. For rings of types A and B. the pulley dimensions shall be as specified in Table J and Eigwi.5.
One of the pulleys shall be free to turn with very low friction and the other shall be driven to rotate the ring. It shall run at a speed between 10 r/mln and 15 r/min.
8 Number of test pieces
A minimum of three test pieces shall be tested.
The number of test pieces should preferably be decided in advance, bearing in mind that the use of five
test pieces will give a lower uncertainty than a test with three test pieces.
9 Preparation of test pieces
9.1 Dumb-bells
Dumb-bell test pieces shall be prepared by the appropriate methods described in 150 23529. DumbbelLs shall, wherever possible, be cut parallel to the grain of the material unless grain effects are to be studied, in which case a set of dumb-bells shall also be cut perpendicubr to the grain.
9.2 RIngs
Ring test pieces shall be prepared by cutting or punching. using the appropriate methods described in ISO 23529. or by moulding.
10 ConditionIng of sample and test pieces
10.1 Time between vulcanization and testing
For all test purposes, the minimum time between vulcanization arid testing shall be 16 h.
For non-product tests, the maximum time between vulcanization and testing shall be 4 weeks and, for evaluations intended to be comparable, the tests shall, as far as possible, be carried out alter the same time interval.
For product tests. whenever possible, the time between vulcanization and testing shall not exceed 3 months. In other cases, tests shaLl be made within 2 months of the date of receipt of the product by the customer.
10.2 Protection of samples and test pieces
Samples and test pieces shall be protected as completely as possible from all external influences likely to cause damage during the interval between vulcanization and testing, e.g. they shall be protected from light and heat.
10.3 ConditIoning of samples
Condition all samples, otherthan those from latex, in accordance with ISO 23529 eta standard laboratory temperature, without humidity control, for not less than 3 Ii prior to cutting out the test pieces.
Condition all prepared latex samples in accordance with ISO 23529 at a standard laboratory temperature, with humidity control, for not less than 96 h prior to cutting out the test pieces.
10.4 Conditioning of test pieces
Condition all test pieces In accordance with ISO 23529. If the preparation of test pieces Involves bulling. the Interval between bulling and testing shall be not less than 16 hand not greater than 72 h.
For tests at a standard laboratory temperature, test pieces that do not require further preparation may be tested immediately, if cut from conditioned test samples. Where additional preparation is involved, a minimum conditioning period of 3 hat standard laboratory temperature shall he allowed.
For tests at temperatures other than a standard laboratory temperature, condition the test pieces at the temperature at which the test is to be conducted for a period sufficient to enable the test pieces to attain substantial equilibrium in accordance with ISO 23529 (see also Z42),
11 Marking of dumb-bell test pieces
fusing a non-contact extensometer. mark the dumbiwli test pieces with two reference marks to define the test length as specified in TablLl 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 Lest 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 olthe 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 he 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 circtLmfereflce as tollows.
Internal circumference = ii z Internal diameter
Mean circumference 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 shalt be within 7,5 % of the grand median thickness (or 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.
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/rn in 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.
In making visual measurements, care should be taken to avoid inaccuracies due to parallax.
13.2 Ring test pieces
Set the correct initial distance between the pulleys as follows:
— 30 mm between the centres of the standard pulleys for type A rings;
— 35 mm between the centres of the alternative pulleys for type A rings;
— 5,5mm between the centres of the standard pulleys for type H rings. Set the load to zero before mounting the test piece on the pulleys.
Place the test piece on the pulleys and start the machine, monitoring continuously the distance between the pulleys and the increase in stress throughout the test.
The nominal rate of traverse of the moving pulley shall be 500 mm/mb for type A test pieces and 100 mm/mm for type B test pieces, The drIven pulley shall rotate at the correct speed from the start to the end of the test.
14 Temperature of test
The test shall normally be carried out at one of the standard laboratory temperatures specified in ISO 23S29. When other temperatures are required, these shall be selected from the list of preferred temperatures given in ISO 23529.
The same temperature shall be used throughout any one test or series of tests intended to be comparable.
15 CalculatIon of results
15.1 Dumb-bells
NOTE the rubber Industry uses the term equation for the relationships heretn termed formula. The term formub Is used to describe the table of Ingredients in a rubber compound.
Calculate the tensile strength, TS. expressed In megapascals, using Formula (1):
In FormuLae (1) to (NJ, the symbols used have the following meanings:
Fh is the force recorded at break, in N;
Fm Is the maximum force recorded. In N;
F Is the force recorded at yield, In N;
L0 is the initial test length, in mm;
Lb Is the test Length at break, In mm:
L5 Is the test length at a given stress, in mm;
L Is the test length at yIeld. In mm;
t is the thickness of the test piece over the test length, in mm;
W is the width determined as specified in 1Z1. in mm.
15.2 Ring test pieces
NOTE the rubber Industry uses the term equation for the relationships herein termed formula, The term formula Is used to describe the table or ingredients in a rubber cosnpcnrnd.
Calculate the tensile strength. TS, expressed In megapascals. using Formula (9):
16 Expression of results
When more than one tensile stress•strain property is being determined on the same test pieces, the test data shall be treated as if they had been obtained independently for each property and the result calculated as described for each property separately.
In all cases, the median (or each property shall be reported.
17 Precision
See Annex .
NOTE Annex C analyses, on the basis of the precision data, the performance of the dific-rent types of dumb. bell test piece.
18 Test report
The test report shall include the following particulars:
a) details of sample and test pieces:
1) a full description of the sample and its origin,
2) compound details and cure condition, If known.
3) the method of preparation of the test pieces (e.g. buffing),
4) the type of test piece used.
5) the median thickness of the test piece,
6) the direction relative to any grain in which dumbbell test pieces were cut; b) a full reference to the test method. i.e. ISO 37:
c) test details:
1) the temperature of test and the relative humidity, If necessary.
2) the number of test pieces tested.
3) any deviations from the procedure specified:
d) test results:
1) the individual test results,
2) the median values of the properties determined, calculated in accordance with Clauaei.5:
e) the date of testing.