Self-tighteningTJ-10
Eccentric Roller Grips
The roller rotates as the specimen pulls, so clamping rises with tension and the thinning rubber tab cannot creep out — what D412 asks for and what a manual wedge cannot do.
SpecificationsTesting standard
ASTM D412
Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers—Tension
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ASTM D412 is the tension test for vulcanised rubber and thermoplastic elastomers. A dumbbell die-cut from cured sheet is pulled apart at 500 mm/min until it ruptures, and the method reports tensile strength, ultimate elongation and modulus — which in rubber means the stress reached at a stated elongation, usually 100 % or 300 %, not the slope of the curve.
At a glance
- Test type
- Tensile — the specimen is pulled apart
- Published by
- ASTM
- Edition
- D412-16(2021)
- Material
- Rubber, elastomers & foams
- Runs on
- Series 7200 and Series 9000
What the test does
A dumbbell cut from cured rubber sheet is clamped by its wide end tabs and pulled along its axis until it ruptures. Force is recorded continuously against the separation of two bench marks inked on the unstrained specimen. Method B replaces the dumbbell with a cut ring, which is looped over two spools and drawn apart instead of gripped, so no clamping is involved at all.
What it measures, and why it matters
The method reports tensile strength, ultimate elongation and modulus — in rubber usage, the stress reached at a stated elongation, typically 100 % or 300 %. Modulus at 300 % is the routine proxy for crosslink density, so it is the number a compounder reads to confirm a batch cured as intended, and the number a purchaser writes into a lot-release specification. Ultimate elongation flags overcure and filler dispersion problems. Tensile strength ranks candidate compounds during material selection, and drops in it drive most ageing and failure investigations.
Dies, dimensions and marks
Two methods, and they take entirely different specimens. Method A uses a die-cut dumbbell; Method B uses a cut ring looped over two spools, so nothing is gripped at all.
- Die C — the default
- 6 mm narrow width, 25 mm between bench marksThe die most rubber laboratories mean when they say D412 without qualifying it.
- Dies available
- Six, A through FDies C and D share the 25 mm gauge. The die used must be reported — the numbers are not interchangeable between dies.
- Sheet thickness
- Typically 2.0 to 3.0 mm, uniformMeasured at three points in the narrow section; the median is used in the area.
- Method B specimen
- Cut ring, no bench marksElongation comes from spool separation rather than from marks on the specimen.
- Specimens per sample
- 3 minimum, 5 preferredThe median is reported where five are run, which is why five is worth the extra material.
- Test temperature
- 23 ± 2 °C
- Discard and replace
- Any rupture in the fillet radiusA shoulder break measures the radius, not the compound, and must not be averaged in.
- Check the die edge
- Before every batchDakA blunt die leaves a ragged edge that seeds a tear. It is the single most common cause of a compound that appears to have lost tensile strength overnight.
Cutting matters far more here than in rigid plastics. Rubber is notch-sensitive, so a nick invisible to the eye can halve the tensile strength — and the result looks like a compounding problem rather than a cutting one.
Test speed
- Methods A and B
- 500 ± 50 mm/minGrip separation rate. Fast, so the frame has to hold it steadily rather than average it over the run.
- Thermoplastic elastomers
- Commonly 50 mm/minPracticeSlower, so the yield and cold-drawing region resolves. The trigger for the reduced rate belongs to the standard's own text.
- End of test
- RuptureUnlike the plastics methods there is no strain cut-off — the specimen is taken to failure.
- Confirm the rate under load
- Not just the settingDak500 mm/min with 700 % elongation on a 25 mm gauge means the crosshead travels a long way. A frame that cannot sustain the rate through the run biases every result the same way.
Calculations
Everything is referred to the original cross-section and the original bench-mark distance. Rubber thins enormously under load, and none of that thinning enters these equations.
Tensile strengthTS
TS = F / (w × t)
- TS
- tensile strength at rupture, MPa
- F
- force at rupture, N
- w
- original width of the narrow section, mm
- t
- original median thickness, mm
Ultimate elongationE
E = ((L − L₀) / L₀) × 100
- E
- elongation at rupture, %
- L
- bench-mark separation at rupture, mm
- L₀
- original bench-mark separation, mm — 25 mm for Die C
From the bench marks, not from the crosshead. Crosshead travel includes grip creep and machine compliance, and the error is always in the same direction.
Modulus at a stated elongationM300
M300 = F₃₀₀ / (w × t)
- M300
- stress at 300 % elongation, MPa
- F₃₀₀
- force recorded when the bench marks reach four times their original separation, N
IN RUBBER, MODULUS MEANS THIS — a stress at a stated strain, not the slope of the curve. M300 is the routine proxy for crosslink density and the number a compounder reads to confirm a batch cured as intended.
How the test runs
- 01Condition the cured sheet and check it is of uniform thickness across the area to be cut.
- 02Cut dumbbells with a sharp die, in one clean stroke, avoiding the sheet edges.
- 03Ink two bench marks on the narrow section at the die's gauge distance, on the unstrained specimen.
- 04Measure thickness at three points in the narrow section and take the median.
- 05Set the grips — self-tightening roller or pneumatic side-action, with faces that hold a thinning tab.
- 06Mount the specimen so it hangs straight, with no pre-tension and no twist.
- 07Set the extension measurement to follow the bench marks — optical or long-travel, since travel to rupture is far beyond a clip-on gauge.
- 08Run at 500 ± 50 mm/min to rupture.
- 09Record the force at each stated elongation as it passes — 100 %, 300 %, or whatever the specification calls for.
- 10Note where the specimen ruptured; discard anything that failed in the fillet.
- 11Repeat across at least three specimens, five where the median is to be reported.
The tab thins as the specimen stretches. A manual wedge grip that held it at the start will let it creep out later in the run, and the result is overstated elongation with soft modulus — a curve that looks like a different compound rather than a slipping grip.
Watch the test
Grips and fixtures for this method
Standard 25 mm
Pneumatic Vice Action Grip
The alternative the method also permits: constant air pressure across the jaw face, uniform on every specimen, and gentler on a soft compound than a wedge.
SpecificationsWhat the report has to contain
- Full designation and edition, and whether Method A or Method B was used
- The die used, and the gauge length between bench marks
- Complete compound identification and cure conditions
- Median thickness of each specimen and the cross-sectional area used
- Test temperature
- Rate of grip separation
- Tensile strength at rupture
- Ultimate elongation
- Modulus at each stated elongation required by the specification
- Number of specimens, and the median or mean as specified
- Any specimen discarded, with the reason
What the machine must be capable of
A Die C dumbbell about 6 mm wide and 2–3 mm thick carries modest load: a soft compound peaking near 5 MPa breaks around 100 N, a hard 25 MPa compound near 500 N. A 500 N or 1 kN load cell covers almost every rubber, and a 100–200 N cell resolves low-strain modulus points better. Force indication must meet ASTM E4.
Grip separation runs at 500 ± 50 mm/min for Methods A and B — fast, so the frame must hold that rate steadily, not average it. Thermoplastic elastomers are run slower, around 50 mm/min, so the yield and cold-drawing region can be resolved; the exact trigger condition for that reduced rate is not something this page can state.
Strain travel is the hard requirement. Elongation runs from 0 % to rupture, commonly 100–800 % for vulcanizates and beyond 1000 % for some TPEs and silicones, which on a 25 mm gauge is roughly 25–275 mm of extension — long-travel or optical territory, not a clip-on extensometer. The method calls for grips that tighten automatically and press uniformly across the jaw face, so clamping rises with tension and the thinning tab cannot creep out; self-tightening roller grips or pneumatic side-action grips with serrated or rubber-coated faces satisfy this, manual wedges usually do not. Method B needs the two-spool ring fixture. A chamber is required only when a non-ambient temperature from ASTM D1349 is specified.
What goes wrong in practice
Grip slippage is the standard fault: the tab thins under load, creeps out of a manual wedge, and elongation is overstated while modulus reads soft. Shoulder breaks — rupture in the fillet rather than the gauge section — are invalid and must be discarded, not averaged in. Nicks left by a dull cutting die initiate tears early and depress tensile strength. Taking elongation from crosshead travel rather than bench marks folds grip creep and machine compliance into the strain, so the error is systematic and always in the same direction.
How it differs from the standards nearest to it
| ASTM D412 | ISO 37 | ASTM D638 | |
|---|---|---|---|
| Subject | Vulcanised rubber and TPEs | Vulcanised rubber and TPEs | Rigid and semi-rigid plastics |
| Specimen | Die C dumbbell or cut ring | Type 1 or Type 2 dumbbell | Type I–V dumbbell |
| Gauge length | 25 mm for Dies C and D | 20 or 25 mm by type | 50 mm for Type I |
| Speed | 500 ± 50 mm/min | 500 or 200 mm/min by type | 5 to 500 mm/min, tabulated |
| Modulus means | Stress at a stated elongation | Stress at a stated elongation | Slope of the initial curve |
| Typical elongation | 100–800 % | 100–800 % | 2–100 % |
ISO 37 is the nearest counterpart and tests the same materials, but its dies and speeds differ — results should not be treated as interchangeable without a correlation study. ASTM D638 is the wrong method for an elastomer entirely: its strain range does not reach where rubber lives, and the word modulus does not mean the same thing in the two documents.
Questions we are asked about this test
What is ASTM D412?
It is the ASTM tension test for vulcanised rubber and thermoplastic elastomers. A dumbbell die-cut from cured sheet is pulled apart until it ruptures, and the method reports tensile strength, ultimate elongation and modulus at stated elongations. A second method uses a cut ring drawn over two spools instead of a gripped dumbbell.
What does modulus mean in ASTM D412?
Something quite different from what it means in a plastics or metals standard. Here it is the stress reached at a stated elongation — M300 is the stress when the bench marks have moved to four times their original separation. It is not the slope of the stress–strain curve. M300 is the routine proxy for crosslink density, which is why a compounder reads it to confirm a batch cured as intended.
What die does ASTM D412 use?
Die C is the default, with a 6 mm wide narrow section and 25 mm between bench marks. Six dies are defined in total, and the numbers from different dies are not interchangeable — so the die used has to be reported with the result. The condition of the cutting edge matters as much as its dimensions.
What speed does ASTM D412 use?
500 ± 50 mm/min of grip separation for both the dumbbell and the ring method. Thermoplastic elastomers are commonly run slower, around 50 mm/min, so the yield and cold-drawing region can be resolved. The rate is fast and the extension is long, so the frame has to hold the speed steadily through the whole run rather than average it.
Why must elongation be measured from the bench marks?
Because crosshead travel is not the same as specimen strain. It also contains the machine's own stretch and any creep of the tab through the grips, and both push the elongation figure up while pushing modulus down. On a 25 mm gauge stretching to 700 %, small errors near the grips become large errors in the result.
What is the difference between ASTM D412 and ISO 37?
They cover the same materials and the same property, but the dumbbell dies and the test speeds differ, so the numbers are close rather than equal. Treating them as interchangeable without a correlation study is how a compound passes one specification and fails the other on the same material.
What extensometer do I need for ASTM D412?
One with a very long travel or a non-contact one. Vulcanisates commonly reach 100 to 800 % elongation and some silicones and TPEs pass 1000 %, which on a 25 mm gauge is anywhere from 25 to 275 mm of extension. A clip-on gauge cannot follow that, so the practical choices are a long-travel device or an optical system tracking the bench marks.
What capacity load cell does ASTM D412 need?
Much smaller than most people expect. A Die C dumbbell 6 mm wide and 2 mm thick from a soft compound peaking near 5 MPa breaks at around 100 N; a hard 25 MPa compound near 500 N. A 500 N or 1 kN cell covers almost every rubber, and a 100 to 200 N cell resolves the low-strain modulus points far better than a larger one reaching further up its range.
Why did my specimen break at the shoulder?
A rupture in the fillet radius rather than the parallel section usually means the die left a nick at the transition, or the specimen was clamped out of square so the shoulder carried bending as well as tension. Either way the result is invalid under the method and must be discarded and replaced, not averaged in with the good ones.
Running ASTM D412 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 | A Die C dumbbell is about 6 mm wide and 2–3 mm thick, so a soft compound near 5 MPa peaks around 100 N while a hard 25 MPa compound peaks near 500 N; a 500 N or 1 kN load cell covers almost every rubber, and a 100–200 N cell is better where low-strain modulus points must be resolved. | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | ASTM E4 | Verified to ASTM E4, and to ISO 7500-1 Class 0.5 |
| Gripping | Self-tightening roller grips or pneumatic side-action grips with serrated/rubber-coated faces for dumbbells and straight specimens; a two-spool ring fixture for Method B cut rings. | Our vice-action grips or self-tightening eccentric roller grips, built to the specimen |
| Environment | Ambient standard laboratory temperature, 23 ± 2 °C; humidity control only for moisture-sensitive compounds; a thermostatic chamber only if a non-ambient temperature from ASTM D1349 is specified. | 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.