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
ISO 8067
Flexible cellular polymeric materials — Determination of tear strength
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ISO 8067 specifies two methods for the tear strength of flexible cellular polymeric materials: method A using a trouser test piece, and method B using an angle test piece without a nick. The absence of a nick in method B is the substantive difference.
At a glance
- Test type
- Tear — a cut or nick is forced to grow
- Published by
- ISO
- Edition
- ISO 8067:2018
- Material
- Rubber, elastomers & foams
- Runs on
- Series 7200 and Series 9000
What the test does
A conditioned foam specimen is cut with a sharp die into one of two shapes and pulled apart at a constant rate of grip separation. Method A uses a trouser test piece, whose two legs are gripped and separated. Method B uses an angle test piece with no nick, so the tear must start at the apex of the angle rather than from a prepared cut. The force is averaged according to the method's rule and divided by the specimen thickness, which is measured under a defined light load because foam compresses under any gauge.
What it measures, and why it matters
How readily a foam tears — and, depending on the method chosen, whether that is about starting a tear or continuing one. The missing nick in method B is the substantive difference between them, and it is a real distinction rather than a procedural one: initiation and propagation are separate properties in a cellular material, and a foam can resist one while being poor at the other. A cushion that must survive a snag is asking about propagation; one that must resist being torn at all in handling is asking about initiation.
Two methods, one with no nick
A trouser piece has the tear already started. An unnicked angle piece has to start it, which is a different property.
- Method A
- Trouser test pieceThe tear already exists. This measures propagation.
- Method B
- Angle test piece WITHOUT a nickNo starting cut. The specimen has to initiate its own tear at the apex of the angle, which is a tougher and different question.
- Material
- Flexible cellular polymeric materialsFoams — upholstery, mattress, packaging, automotive seating.
- Result
- A force normalised by thickness
- Grip pressure
- Enough to hold, no moreFoam crushes. An over-tightened jaw creates a dense line the tear runs to.
- Cut specimens with a sharp die, and check the die
- DakA blunt die tears foam rather than cutting it, leaving a ragged edge that is already half a tear.
Method B's missing nick is the whole distinction. Initiation and propagation are separate properties in a cellular material, and a foam can resist one while being poor at the other.
Test speed
- Rate
- A constant rate of grip separation as specified
- Reported
- Tear strength, with the method letterA value without A or B cannot be interpreted.
- Density
- Recorded, since foam properties track it closelyDak
- Keep the trace
- Foam tear traces are irregular by natureDakThe tear jumps from cell wall to cell wall, so the record is jagged and the averaging rule matters.
Calculations
Tear strength—
Force divided by the specimen thickness
Normalised by thickness, so the thickness measurement carries directly into the result — and foam thickness is measured under a defined light load because the material compresses.
Why method B is different—
No nick means initiation is included
Method A measures how easily an existing tear runs; method B measures how easily one starts and then runs. The two rank foams differently.
How the test runs
- 01Condition the foam as specified.
- 02Record the density, since foam properties track it closely.
- 03Choose method A or method B from the specification.
- 04Cut test pieces with a sharp die, inspecting the die first.
- 05For method A, form the trouser legs; for method B, cut the angle with no nick.
- 06Measure the thickness under the defined light load.
- 07Fit light grips and set a pressure that holds without crushing the cells.
- 08Separate at the specified constant rate.
- 09Record the trace and apply the method's averaging rule.
- 10Divide by the thickness to give tear strength.
- 11Report the method letter with every value.
The fixture this method needs
What the report has to contain
- Reference to ISO 8067 and the edition
- Which method was used — A or B
- Material, cell structure and density
- Conditioning atmosphere
- Measured thickness and the load it was measured under
- Rate of grip separation
- Force and the calculated tear strength
- Description of the trace
- Number of specimens rejected and why
- Any specimen where the tear left the intended path
What the machine must be capable of
Very small forces, measured traceably — foam tear forces are commonly a few newtons, well below the range a frame's own load cell describes accurately. Grips must hold without crushing, which on a light open-cell foam means very little pressure indeed, less than feels reassuring: an over-tightened jaw creates a dense, stiff band along the clamp line and the tear runs to that band instead of through representative material. Long, steady travel is needed, as with any tear test.
What goes wrong in practice
Reporting a value without the method letter, when A and B measure different properties and rank foams differently. Over-tightened grips crushing the cells. A blunt die. Measuring thickness by squeezing the foam, which shortens the divisor and inflates the tear strength. And reading a single peak off a trace that is jagged by nature — the tear advances cell wall by cell wall, which is exactly why the method specifies an averaging rule rather than leaving the reading to judgement.
ISO 8067 method A or method B
| Method A — trouser | Method B — angle, no nick | |
|---|---|---|
| Tear exists at the start | Yes | No |
| Measures | Propagation | Initiation and propagation together |
| Comparable with each other | No | No |
| Both report | Force per unit thickness | Force per unit thickness |
Choosing between them is choosing which question to ask. A cushion that must not tear once snagged wants method A; one that must resist being torn at all wants method B.
Questions we are asked about this test
What is ISO 8067?
It is the ISO tear strength method for flexible cellular polymeric materials — foams used in upholstery, mattresses, packaging and vehicle seating. It specifies two methods: method A with a trouser test piece, and method B with an angle test piece that has no nick. The current edition is ISO 8067:2018, with a revision in the approval phase.
Why does method B have no nick?
So that the specimen has to start its own tear. A trouser piece arrives with the tear already made, so it measures only how easily an existing one propagates. An unnicked angle piece concentrates stress at the apex and the foam must initiate a tear there before anything can run. Initiation and propagation are separate properties in a cellular material, and a foam can be good at resisting one and poor at the other.
Which method should I use?
Whichever the specification names, and the choice is a real one rather than a formality. A cushion that must survive being snagged is asking about propagation, which is method A. A foam that must resist being torn at all in handling is asking about initiation, which method B includes. The two rank materials differently, so a value reported without its method letter cannot be interpreted.
Why is grip pressure such a problem with foam?
Because foam is compressible in a way solid rubber is not. A jaw tightened as it would be for a solid crushes the cells along the clamp line, creating a dense, stiff band, and the tear then runs to that band rather than through representative material. The pressure has to be just enough to hold — which on a light, open-cell foam is very little indeed.
Why is the result divided by thickness?
To make foams of different thickness comparable, in the same way film tear is normalised. It means the thickness measurement carries directly into the answer, and foam thickness is not a simple measurement: the material compresses under any gauge, so it is measured under a defined light load rather than by closing callipers on it.
Why is the force trace irregular?
Because a tear in foam advances from cell wall to cell wall rather than through a continuous solid. Each wall resists and then ruptures, so the record is jagged by nature rather than by fault. That is why the method specifies how to average it — reading a single peak from such a trace would report whichever cell wall happened to be strongest.
Why record the density?
Because almost every mechanical property of a foam tracks its density closely, tear strength included. Two samples of the same chemistry at different densities are effectively different materials, so a tear result without a density is hard to compare with anything and impossible to use in selecting a grade.
Running ISO 8067 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 | Very low — foam tear forces are commonly a few 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 | Verified at the actual tear force, which is a very small fraction of most frames | ISO 7500-1 Class 0.5, verified to ASTM E4, DIN 51221 and BS 1610 |
| Gripping | Grips holding the two legs of a trouser piece, or the two ends of an angle piece | Wedge, vice-action, pneumatic and hydraulic 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.