Standard 25 mm
Pneumatic Vice Action Grip
Pneumatic vice action grips clamp the full specimen width at a constant, even pressure — which is what stops one side slipping or tearing before the other.
SpecificationsTesting standard
IS 3400 (Part 1)
Methods of Test for Vulcanized Rubber — Part 1: Tensile Stress-Strain Properties
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
IS 3400 (Part 1) is the Bureau of Indian Standards method for the tensile stress-strain properties of vulcanized and thermoplastic rubber. It is aligned with ISO 37, and gives tensile strength, elongation at break, stress at a given elongation and elongation at a given stress.
At a glance
- Test type
- Tensile — the specimen is pulled apart
- Published by
- BIS
- Edition
- 2021
- Material
- Rubber, elastomers & foams
- Runs on
- Series 7200 and Series 9000
What the test does
A dumb-bell is cut from vulcanized sheet with a sharp die, conditioned after vulcanization, and its narrow portion measured and gauge-marked. It is gripped in pneumatic jaws and extended at 500 mm/min for most dumb-bell types, with strain followed by a non-contacting extensometer on the gauge marks. The run yields tensile strength, elongation at break, stress at a given elongation, elongation at a given stress, and — for some thermoplastic rubbers and certain compounds — the stress and strain at yield.
What it measures, and why it matters
Several properties, and the one most people quote is often not the one the specification uses. Tensile strength gets the headline, but rubber compounds are usually bought and sold against stress at a stated elongation — M100, M300 and similar — because those describe the material at the strains it actually works at, whereas the breaking strength describes a condition a seal or a mount will never see. Both are calculated on the original cross-section by convention: rubber thins enormously before it breaks, so the true stress at failure is far higher than the number reported, and the convention exists to make laboratories comparable rather than to be physically true.
What it yields
Not one number but several, and the ones a rubber specification actually uses are often the modulus values rather than the strength.
- Tensile strength
- Force at break over the original section
- Elongation at break
- PercentageCommonly several hundred per cent, which is why a contacting extensometer is unsuitable.
- Stress at a given elongation
- Often called the modulusM100, M300 and similar. This is what most rubber specifications are actually written against.
- Elongation at a given stress
- The inverse quantity
- Stress and strain at yield
- Only for some thermoplastic rubbers and certain compounds
- Cut dumb-bells with a sharp die on a clean backing
- DakA nick in the edge of a rubber dumb-bell is a tear origin, and rubber tears from nicks at a fraction of its tensile strength.
Rubber is aligned with ISO 37 in India, and ISO 37 has moved to its seventh edition. Confirm which ISO edition the current IS revision adopts before claiming the two results are interchangeable.
Test speed
- Rate
- 500 mm/min for most dumb-bells
- Reported
- Tensile strength, elongation at break, and stress at stated elongations
- Strain
- Non-contacting extensometerA clip-on gauge loads a soft specimen and slips off at high extension.
- Discard specimens that broke outside the narrow section
- Dak
Calculations
Tensile strengthTS
TS = F / (w × t)
- F
- force at break, N
- w
- width of the narrow portion, mm
- t
- thickness, mm
On the original cross-section, measured on the specimen. Rubber thins enormously before it breaks and none of that is accounted for.
Elongation at breakEb
Eb = (L − L₀) / L₀ × 100
- L
- gauge length at break
- L₀
- original gauge length
Measured on gauge marks, not from the crosshead. Grip take-up and the shoulders of the dumb-bell both extend, and neither belongs in the gauge.
Stress at a given elongationM
M = F at the stated elongation / original cross-section
- F
- force when the gauge marks reach the stated elongation
Conventionally called the modulus, though it is not a modulus in the elastic sense — it is a stress at a strain, and the strain has to be stated.
How the test runs
- 01Prepare sheet to the specified thickness and condition it after vulcanization.
- 02Cut dumb-bells with a sharp die on a clean backing, in the specified direction.
- 03Inspect every edge for nicks and discard any specimen that has one.
- 04Measure the width and thickness of the narrow portion.
- 05Mark the gauge length.
- 06Fit pneumatic grips at a pressure that holds without distorting the specimen.
- 07Fit a non-contacting extensometer to the gauge marks.
- 08Load at 500 mm/min unless the specification says otherwise.
- 09Record force and gauge extension to break.
- 10Calculate tensile strength, elongation at break and the required stress-at-elongation values.
- 11Discard specimens that broke outside the narrow section, and record how many.
The fixture this method needs
What the report has to contain
- Reference to IS 3400 (Part 1) and the edition
- Compound identification and cure conditions
- Sheet thickness and dumb-bell type
- Direction of cutting relative to the sheet
- Conditioning after vulcanization
- Measured width and thickness of the narrow portion
- Gauge length and how strain was measured
- Rate of traverse
- Tensile strength, elongation at break, and stress at each stated elongation
- Number of specimens discarded and why
What the machine must be capable of
Modest force but a great deal of travel. Rubber dumb-bells commonly break between a few tens and a few hundred newtons, while reaching elongations of several hundred per cent, so the frame needs the stroke more than the capacity. Grips must hold a soft specimen without squeezing it out of shape, which is why pneumatic jaws at a controlled pressure are preferred to screw grips tightened by hand. Strain is followed by a non-contacting extensometer, since a clip-on gauge both loads the specimen and cannot survive the extension.
What goes wrong in practice
Assuming an IS result automatically satisfies the current ISO 37, when an adopted standard does not move as its parent does. Nicked specimens, which read low and look like material variability. Taking elongation from the crosshead, which includes grip take-up and the extension of the dumb-bell shoulders, neither of which belongs in the gauge. Reporting tensile strength when the specification asks for a stress at elongation. And omitting the cutting direction, which leaves a real variable unrecorded.
IS 3400 (Part 1) or ISO 37
| IS 3400 (Part 1) | ISO 37 | |
|---|---|---|
| Published by | BIS | ISO |
| Relationship | Aligned with ISO 37 | The parent method |
| Current | IS 3400 (Part 1) : 2021 | ISO 37:2024, seventh edition |
| Assume equivalence | Only after checking the adopted edition | — |
An Indian Standard adopted from an ISO method does not move when the ISO method does. Check which ISO edition the IS revision in force actually adopts before treating a result as satisfying both.
Questions we are asked about this test
What is IS 3400 (Part 1)?
It is the Bureau of Indian Standards method for the tensile stress-strain properties of vulcanized and thermoplastic rubber — tensile strength, elongation at break, stress at a given elongation, elongation at a given stress, and for some thermoplastic rubbers the stress and strain at yield. It is aligned with ISO 37, and the current edition is IS 3400 (Part 1) : 2021.
Is an IS 3400 (Part 1) result the same as an ISO 37 result?
Usually, but it should be checked rather than assumed. The Indian Standard is adopted from ISO 37, and the 2012 third revision was identical with ISO 37:2011. ISO 37 has since moved on and is now in its seventh edition, ISO 37:2024. An adopted standard does not update when its parent does, so before treating one result as satisfying both, confirm which ISO edition the IS revision in force actually adopts.
What is meant by the modulus of a rubber?
Conventionally, the stress at a stated elongation — M100 is the stress at 100 % elongation, M300 at 300 %, and so on. It is not a modulus in the elastic sense, since it is a stress at a strain rather than a slope, but the usage is universal in the rubber trade. Most rubber specifications are written against these values rather than against tensile strength, because they describe the compound at the strains it actually works at.
Why can't a clip-on extensometer be used?
Two reasons. It loads the specimen — a soft rubber dumb-bell is stiff enough to be influenced by the weight and spring force of a contacting gauge — and it cannot survive the travel, since rubber elongations at break commonly run to several hundred per cent. A non-contacting extensometer following gauge marks handles both, which is why it is the normal arrangement for this method.
Why does a nick in the specimen matter so much?
Because rubber tears far more easily than it pulls apart. A small nick in the edge of a dumb-bell is a tear origin, and the specimen will fail from it at a fraction of the tensile strength the compound would otherwise show. It is the single most common cause of a low outlier, which is why every edge is inspected before testing and cutting is done with a sharp die on a clean backing.
Why is the strength calculated on the original cross-section?
By convention, and everyone using the figure needs to know it is a convention. Rubber thins enormously before it breaks — a dumb-bell at four hundred per cent elongation has a section a fraction of what it started with — so the true stress at failure is far higher than the reported tensile strength. The original-section basis is what makes results comparable between laboratories, not what makes them physically true.
Does the direction of cutting matter?
Yes, on milled or calendered sheet. Rubber sheet carries a grain from processing, and dumb-bells cut along and across it can differ measurably in both strength and elongation. The direction is recorded for that reason, and a specification that does not name one leaves a variable open that will show up as scatter between laboratories cutting differently.
Running IS 3400 (Part 1) on the Series 7200 and Series 9000
Dak verifies against whichever standard the method names, and where a class applies our frames sit a class tighter than it asks.
| The method asks for | Dak supplies | |
|---|---|---|
| Capacity | Low — rubber dumb-bells commonly break between a few tens and a few hundred newtons | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | Class 1 over the working range | ISO 7500-1 Class 0.5, verified to ASTM E4, DIN 51221 and BS 1610 |
| Strain measurement | An extensometer of the class the method specifies | Certified to ISO 9513 Class 1 and ASTM E83 — non-contact video, clip-on and high-elongation |
| Gripping | Pneumatic grips holding a dumb-bell without pre-stressing it, and a non-contacting extensometer | Our pneumatic grips, built to the specimen |
| Environment | 23 ± 2 °C standard laboratory atmosphere | 3009 series chambers, −150 °C to +400 °C — temperature only |
This page describes the method as practised. The governing text is the current edition from the issuing body. Tell us what you are testing and we will answer with the machine, the fixture and a quotation.