ISO 1924-2

What the test does

Conditioned strips are cut in the machine and cross directions and pulled at a constant rate of elongation of 20 mm/min until they break, with force and elongation recorded throughout. Three quantities come directly from the run: the tensile strength as maximum force per unit width, the strain at break, and the tensile energy absorption, which is the area under the force-elongation curve. The standard also supplies equations for the tensile index, the TEA index and the modulus of elasticity, all of which normalise by grammage.

What it measures, and why it matters

How strong the sheet is, how far it stretches, and how much work it absorbs before failing. The third of these is the one most easily overlooked and often the most useful: TEA combines strength and stretch into a toughness figure, and two papers of identical tensile strength can differ markedly in it. The tougher one survives converting, printing and handling better, which is why sack and bag papers are specified on TEA as much as on strength. Everything is normalised by grammage rather than thickness, because a sheet compresses under the gauge and its thickness depends on how hard it was measured.

The rate is the standard

Part 2 runs at 20 mm/min and Part 3 at 100 mm/min. They are the same test at different speeds, and they do not give the same numbers.

Rate

20 mm/minWritten into the title, which is unusual and deliberate.

Part 3

The same method at 100 mm/minCiting ISO 1924 without the part number is not enough to reproduce a result.

Tensile strength

Maximum force per unit width

Strain at break

Percentage

Tensile energy absorption

The area under the force-elongation curveTEA describes toughness — how much work the sheet absorbs before it fails, which a strength figure alone misses.

Index values

Normalised by grammage, not by thicknessPaper thickness is compressible and depends on how hard it is measured. Grammage does not.

Paper is normalised by grammage. Tensile index is strength divided by grammage, and it is the figure that lets a light sheet and a heavy one be compared at all.

Test speed

Rate

20 mm/min

Reported

Tensile strength, strain at break, TEA, and the index values

Directions

Machine and cross direction, separatelyPaper is strongly oriented by the machine that made it; MD and CD routinely differ by a factor of two or more.

Never cite ISO 1924 without the part

Dak

Calculations

How the test runs

1. 01Condition the paper in the standard atmosphere.
2. 02Determine the grammage, since the index values depend on it.
3. 03Cut strips of the specified width in the machine and cross directions.
4. 04Handle the strips by their ends — a crease is a failure origin.
5. 05Fit wide pneumatic grips and set a pressure that holds without crushing.
6. 06Set the gauge length and a rate of 20 mm/min.
7. 07Load to break, recording force and elongation throughout.
8. 08Determine the maximum force, the strain at break and the area under the curve.
9. 09Calculate tensile strength per unit width, tensile index and TEA index.
10. 10Reject specimens that broke at the jaws or on a crease.
11. 11Report the part number, because Part 3 runs at a different rate.

The fixture this method needs

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.

Specifications

What the report has to contain

• Reference to ISO 1924-2 and the edition
• Paper or board identification and grammage
• Direction tested and specimen width
• Conditioning atmosphere
• Gauge length and rate of elongation
• Tensile strength per unit width
• Tensile index
• Strain at break
• Tensile energy absorption and TEA index
• Number of specimens rejected and why

What the machine must be capable of

Low force, a well-controlled slow rate, and grips that hold a sheet without crushing it. Most papers break between a few newtons and a few hundred, so the load cell is sized for the paper rather than for the frame. The rate matters as much as the force here — 20 mm/min is not a default but a defining parameter, and a machine that cannot hold it accurately is producing Part 3 results under a Part 2 heading. Elongation is normally taken from grip separation, which the method accommodates.

What goes wrong in practice

Citing ISO 1924 without the part number, which leaves a reader unable to tell whether the result came from 20 or 100 mm/min on a rate-sensitive material. Averaging machine and cross direction. Computing a stress from a measured thickness instead of using the grammage-normalised index. Creased or crushed specimens, which read low and look like material variability. And reporting strength alone where the application is actually governed by toughness, which is what TEA exists to describe. The last one is quiet but common: determining the index values from a nominal grammage taken off the specification rather than from the grammage of the sheet actually tested, which puts an error straight into every normalised figure.

ISO 1924-2 or ISO 1924-3

Paper is rate-sensitive, so the same sheet gives different numbers at 20 and 100 mm/min. The rate is in each part's title precisely so that citing the part is enough to reproduce the result.

Questions we are asked about this test