ISO 37:2017 pdf free
ISO 37:2017 pdf free.Rubber, vulcanized or thermoplastic一Determination of tensile stress-strain properties
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 elongation are taken as required during the uninterrupted stretching of the test piece and when it breaks.
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-section. 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, sormetimes 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 grain if this is present to a significant degree.
Dumb-bells shall be used if it is required to study grain effects, as rings are not suitable for this purpose.
c) Elongation at a given stress and stress at a given elongation
The larger dumb-bells (types 1, 2 and 1A) 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 if 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.ISO 37 pdf download.
