Standard 25 mm
Pneumatic Vice Action Grip
Pneumatic vice action grips hold the full specimen width at an even pressure, which matters here because a seam loaded unevenly begins failing at one end and the peak force is lost.
SpecificationsTesting standard
ISO 13935-1 / -2
Textiles — Seam tensile properties of fabrics and made-up textile articles
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ISO 13935 measures the seam tensile properties of fabrics and made-up articles. A specimen containing a seam is pulled perpendicular to it until the seam fails, and the maximum force is reported together with how it failed. Part 1 uses a full-width strip and Part 2 a grab geometry. In most garments the seam is weaker than the fabric, which is why this test exists.
At a glance
- Test type
- Tensile — the specimen is pulled apart
- Published by
- ISO
- Edition
- ISO 13935-1:2014
- Runs on
- Series 7200 and Series 9000
What the test does
A specimen containing a seam is prepared so that the seam runs perpendicular to the direction of pull and sits midway between the grips. Under Part 1 the full specimen width is clamped in flat-faced grips; under Part 2 narrower grab jaws hold the centre of a wider specimen. A small pretension removes slack, and the crosshead separates at the specified rate — commonly 50 or 100 mm/min — over a gauge length of about 200 mm. Force is recorded until the seam fails, and the maximum force is reported. The way it failed is recorded alongside: thread rupture, seam slippage, stitch pull-out, or rupture of the fabric itself.
What it measures, and why it matters
The result is the maximum seam force and the mechanism of failure. It matters because a made-up textile article almost never fails in the middle of a panel — it fails at a seam. Sewing perforates the fabric, concentrates load into discrete stitch holes and introduces a discontinuity into an otherwise continuous material, so the seam is usually the weakest element in the product. Expressed against the fabric's own strength as a seam efficiency, the figure tells a manufacturer how much of the material they paid for is actually available in the finished article, and where to spend effort to recover the rest.
Specimen and seam
The seam is the specimen. Everything about how it was sewn — thread, stitch type, stitch density, seam allowance — is a variable, and none of it can be reconstructed afterwards.
- Seam orientation
- Perpendicular to the direction of pull
- Seam position
- Midway between the gripsA seam close to one jaw is influenced by the clamping, and the result drifts.
- Part 1
- Strip method, full specimen width clamped
- Part 2
- Grab method, narrower jaws on a wider specimen
- Seam construction
- Recorded in fullThread type and size, stitch type, stitches per centimetre and seam allowance. Two seams in the same fabric can differ by a factor of two.
- Conditioning
- 20 ± 2 °C and 65 ± 4 % RH
- Take specimens from the actual garment seam
- Where the question is about a productDakA laboratory-sewn seam tests the specification; a production seam tests what was actually made, and the two frequently disagree.
The failure mode is the finding. Seam slippage, thread rupture, stitch pull-out and fabric rupture each point at a different cause and a different fix, and a maximum force reported without the mode leaves the most useful part of the test unreported.
Test speed
- Rate
- Commonly 50 or 100 mm/min, per the relevant part
- Gauge length
- 200 mm typical
- Reported value
- Maximum seam force
- Stop at seam failure, not fabric failure
- Where they differDakIf the fabric goes first, the seam was stronger than the fabric — a valid and useful outcome, but it is not a seam strength.
Calculations
Maximum seam forceF
The maximum force recorded before seam failure, in N
Reported as a force for the stated specimen geometry, not normalised to a width.
Seam efficiency—
Seam efficiency = maximum seam force / fabric breaking force × 100
A useful derived figure where the fabric's own breaking force is known from ISO 13934 on the same material. It says how much of the fabric's strength the seam preserved.
How the test runs
- 01Prepare specimens containing the seam, perpendicular to the pull direction.
- 02Record the full seam construction — thread, stitch type, density, allowance.
- 03Condition at 20 ± 2 °C and 65 ± 4 % RH.
- 04Select the part — strip or grab geometry.
- 05Fit grips appropriate to the part and set the gauge length.
- 06Mount the specimen with the seam midway between the grips and square to the pull.
- 07Apply a small pretension to remove slack.
- 08Pull at the specified rate, recording force.
- 09Record the maximum force at seam failure.
- 10Classify the failure — slippage, thread rupture, stitch pull-out or fabric rupture.
- 11Repeat for the required number of specimens.
Grips and fixtures for this method
Rubber facedTJ-34
25mm Square Vice Action Grip
A 25 mm square vice grip provides the grab geometry Part 2 specifies.
SpecificationsWhat the report has to contain
- Reference to ISO 13935 and which part was used
- Fabric identification and construction
- Full seam construction — thread type and size, stitch type, stitches per centimetre, seam allowance
- Whether the seam was laboratory-sewn or taken from production
- Specimen dimensions and gauge length
- Conditioning atmosphere and duration
- Rate of extension
- Maximum seam force for each specimen
- Failure mode for each specimen, classified
- Seam efficiency where the fabric strength is known
- Mean, standard deviation and coefficient of variation
What the machine must be capable of
Force measurement to ISO 7500-1 Class 1 across a range from a hundred newtons or so to several kilonewtons, and a crosshead holding the specified rate over a 200 mm gauge. Grips must clamp the full specimen width evenly for Part 1, which favours pneumatic actuation, and must present the correct jaw geometry for Part 2. Alignment matters in a particular way here: the seam has to sit square to the pull and midway between the jaws, because a seam that is skewed or close to a grip begins failing at one end and the peak force is never developed. The laboratory needs the textile standard atmosphere.
What goes wrong in practice
Reporting a maximum seam force without the failure mode is the commonest and most costly error, because the mode is what says which change will help — thread rupture, slippage, pull-out and fabric rupture each point to a different fix, and the force alone distinguishes none of them. Skewed or off-centre seams give low results that look like poor sewing. Failing to record the seam construction makes a result unrepeatable even in the same laboratory. And comparing Part 1 with Part 2 figures, or with a fabric strip result, mixes geometries that are not convertible.
ISO 13935-1 or ISO 13935-2
| Part 1 — strip | Part 2 — grab | |
|---|---|---|
| Clamping | Full specimen width | Narrower jaws on a wider specimen |
| Load distribution | Even across the seam | Concentrated, with surrounding fabric assisting |
| Typical result | Lower | Higher |
| Best for | Comparing seam constructions | Quick acceptance testing of made-up articles |
As with fabric tensile testing, the strip and grab geometries give different numbers on the same seam and cannot be converted between. A specification naming one part is not satisfied by running the other.
Questions we are asked about this test
What is ISO 13935?
It is the ISO standard for seam tensile properties of fabrics and made-up textile articles. A specimen containing a seam is pulled perpendicular to that seam until it fails, and the maximum seam force is reported along with the failure mode. Part 1 uses a strip geometry with the full width clamped; Part 2 uses a grab geometry.
Why test the seam rather than the fabric?
Because in most made-up articles the seam is the weakest element. Sewing perforates the fabric, concentrates load into the thread and the stitch holes, and introduces a discontinuity in an otherwise continuous material. A garment, a bag or a technical textile assembly nearly always fails at a seam rather than in the middle of a panel, so the fabric's own strength is not what governs the product.
What are the failure modes and what does each mean?
Thread rupture means the sewing thread was the weak link — use a stronger thread. Seam slippage means the fabric yarns pulled away from the stitching rather than anything breaking, which points to a loose weave or too small a seam allowance. Stitch pull-out means the stitches tore through the fabric, often from too high a stitch density perforating the material. Fabric rupture means the seam was stronger than the fabric, which is usually the desired outcome.
What is seam efficiency?
The maximum seam force expressed as a percentage of the fabric's own breaking force, measured on the same material to ISO 13934. It says how much of the fabric's strength the seam preserved. It is a more useful comparative figure than seam force alone, because a seam force of 500 N is excellent on a light fabric and poor on a heavy one.
Should I test laboratory-sewn or production seams?
It depends what you are asking. A laboratory-sewn seam made to the specification tests whether the specification is adequate. A seam cut from actual production tests what was really made — including thread substitutions, machine tension drift and operator variation. The two frequently disagree, and where a product has failed in the field it is the production seam that holds the answer.
Why does stitch density matter in both directions?
Because it works against itself. Too few stitches per centimetre and the load concentrates on each one, causing pull-out or thread rupture. Too many and the needle perforates the fabric so often that it becomes a line of holes, weakening the material along exactly the line that is being loaded. There is an optimum for every fabric and thread combination, and this test is how it is found.
Can I compare Part 1 and Part 2 results?
No. As with fabric tensile testing, the strip and grab geometries distribute load differently — in the grab test the fabric outside the jaws assists — so the same seam gives a higher number under Part 2. There is no conversion factor, and a specification naming one part is not satisfied by running the other.
Running ISO 13935-1 / -2 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 to moderate — commonly 100 N to 3 kN depending on fabric and seam construction | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | ISO 7500-1 Class 1 over the working range | ISO 7500-1 Class 0.5 — a class tighter than the method asks |
| Gripping | Flat-faced grips — full-width strip clamping for Part 1, or 25 mm grab jaws for Part 2 | Wedge, vice-action, pneumatic and hydraulic grips, built to the specimen |
| Environment | 20 ± 2 °C and 65 ± 4 % RH, the textile standard 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.