ISO 13935-1 / -2 Seam Strength Testing of Fabrics and Textile Articles

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 a constant rate: 100 mm/min over a 200 mm ± 1 mm gauge under Part 1, and 50 mm/min over a 100 mm ± 1 mm gauge under Part 2, each rate held to ±10 %. 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 — Part 1, strip method

100 mm/min, on a 200 mm ± 1 mm gauge

Rate — Part 2, grab method

50 mm/min, on a 100 mm ± 1 mm gauge

Rate tolerance

±10 %

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.

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 100 mm/min to ±10 % over a 200 mm gauge for Part 1, or 50 mm/min over a 100 mm gauge for Part 2. Where force is captured by data acquisition, the sampling frequency must be at least eight readings per second. 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.

Grips and fixtures for this method

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.

Specifications

Rubber facedTJ-34

25mm Square Vice Action Grip

A 25 mm square vice grip provides the grab geometry Part 2 specifies.

Specifications

How the test runs

1. 01Prepare specimens containing the seam, perpendicular to the pull direction.
2. 02Record the full seam construction — thread, stitch type, density, allowance.
3. 03Condition at 20 ± 2 °C and 65 ± 4 % RH.
4. 04Select the part — strip or grab geometry.
5. 05Fit grips appropriate to the part and set the gauge length.
6. 06Mount the specimen with the seam midway between the grips and square to the pull.
7. 07Apply a small pretension to remove slack.
8. 08Pull at 100 mm/min for Part 1, or 50 mm/min for Part 2, recording force.
9. 09Record the maximum force at seam failure.
10. 10Classify the failure — slippage, thread rupture, stitch pull-out or fabric rupture.
11. 11Repeat for the required number of specimens.

Calculations

What 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 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.