ISO 1924-2
Tensile Properties of Paper and Board (20 mm/min)

Universal Grip ISO 1924-2 paper tensile vise grip

Downloads: ISO 1924-2 Paper Tensile Vise Grip – Universal Grip Data Sheet (PDF)

Written by Chris Thomas, Universal Grip Company · Reviewed by Frank Bertini · Updated October 24, 2026

ISO 1924-2 is the international standard for the tensile properties of paper and board at a constant rate of elongation of 20 mm/min. A 15 mm wide strip is clamped at a 180 mm test span and extended until it breaks, and the force-elongation curve gives tensile strength in kN/m, strain at break in percent and tensile energy absorption in J/m², from which tensile index, TEA index and modulus of elasticity follow. It is the everyday strength test of paper mills, converters and packaging labs in Europe and much of Asia, the lineage of the old DIN 53112, and the ISO sibling of ASTM D828 and TAPPI T 494. The current edition is ISO 1924-2:2008; a revision is in draft.

This guide covers the edition history and the Part 2 / Part 3 split; the specimen, span and speed rules with their tolerances; the clamp requirements the standard actually writes down (clamping lines parallel within 1°, line contact advised, breaks within 10 mm of a clamp rejected); conditioning per ISO 187; a step-by-step procedure; every formula with a checked worked example and unit conversions; common errors with their size; a four-method comparison with ISO 1924-3, TAPPI T 494 and ASTM D828; and the grips, cutters, extensometers and machines Universal Grip supplies, including our ISO 1924-2 vise grip.

In this guide: What ISO 1924-2 Measures and Where It Applies · Editions: Part 1, Part 2 and Part 3 · Specimens, Span and Speed · Clamps: What the Standard Requires · Conditioning per ISO 187 · Step-by-Step Procedure · Formulas and a Worked Example · Common Errors and Their Size · ISO 1924-2 vs ISO 1924-3 vs TAPPI T 494 and ASTM D828 · Equipment for ISO 1924-2: Grips, Cutters, Extensometers, Machines · FAQ

What ISO 1924-2 Measures and Where It Applies

ISO 1924-2 measures tensile strength as a matter of course, and strain at break and tensile energy absorption by agreement, on strips extended at 20 mm/min. The 2008 edition defines:

Tensile strength: the maximum tensile force per unit width of the strip, in kN/m. A 15 mm strip breaking at 60 N has a tensile strength of 4.0 kN/m.
Tensile index: tensile strength divided by grammage, in Nm/g. It removes basis weight so that a 60 g/m² and a 120 g/m² sheet can be compared fibre for fibre.
Strain at break: the elongation at rupture divided by the initial test length, in percent. The 2008 edition uses 'strain', not the TAPPI term 'stretch'.
Tensile energy absorption (TEA): the work done to the maximum force divided by the test area (test length × width), in J/m². It is the property that predicts whether a sack or a web survives a shock.
TEA index: TEA divided by grammage, in J/g; and modulus of elasticity: the maximum slope of the force-elongation curve times the test length divided by width and thickness, in MPa, with thickness per ISO 534.

Scope: all papers and boards, including high-strain papers within the machine's capacity, and the components of corrugated board (liner and fluting) but not combined corrugated board itself, which goes to edge-crush and box-compression methods. Tissue is tested under ISO 12625-4, laboratory handsheets under ISO 5270, and wet tensile strength under ISO 3781. Tensile stiffness is not a Part 2 property; it belongs to ISO 1924-3 and TAPPI T 494.

Editions: Part 1, Part 2 and Part 3

ISO 1924-1 was the constant-rate-of-loading method and was withdrawn in 2004; nothing current uses it.
ISO 1924-2:2008 (third edition, December 2008) replaced the 1994 edition, renamed the properties to match Part 3 ('strain at break', 'tensile energy absorption') and realigned the clause structure. It was confirmed in 2012, 2018 and 2023 and marked 'to be revised' in 2024; an ISO/DIS 1924-2 is in draft and nothing has been published. Identical texts: EN ISO 1924-2:2008, BS EN ISO 1924-2:2008, DIN EN ISO 1924-2.
ISO 1924-3:2005 is the fast method: 100 mm test span at 100 mm/min (100 %/min against Part 2's 11 %/min), with tensile stiffness added and a tighter elongation requirement. It descends from the Nordic SCAN-P methods, Part 2 from the German DIN 53112 lineage.

The two parts give different numbers on the same paper. The interlaboratory work behind Part 3 found results 5 to 15 % higher at the faster strain rate, and there is no general conversion between them; a specification must name the part. If a customer quotes a tensile index with no method, ask which.

Specimens, Span and Speed

Strip width 15 mm ± 0.1 mm, edges parallel within ± 0.1 mm, cleanly cut with a precision strip cutter and free of damage. There is no 25 mm alternative in ISO 1924-2; 25 mm belongs to TAPPI T 494 and ASTM D828.
Test span 180 mm ± 1 mm between the clamping lines. Strips are cut long enough to clamp at both ends, in practice about 250 mm.
Rate of elongation (20 ± 5) mm/min, which on 180 mm is a strain rate of about 11 % per minute.
Shorter span by agreement for high-stretch papers or small samples, with the rate reset to (10 ± 2.5) % of the unstressed test length per minute, so a 100 mm span runs at 10 mm/min and remains a Part 2 test.
Number of test pieces: at least 10 in the machine direction and at least 10 in the cross direction, and 10 valid results per direction after rejections.
Grammage per ISO 536 on the same sample for the indices; thickness per ISO 534 at 100 ± 10 kPa if the modulus is wanted.

Cut MD and CD strips from the sheet with the grain marked; MD tensile strength is typically 1.5 to 3 times the CD value on machine-made paper, and mixing directions is the fastest way to a meaningless mean. Handle strips by the ends only; moisture and oil from fingers in the 180 mm test zone lower the result.

Clamps: What the Standard Requires

Most of the grip-relevant content in the standard is in its apparatus clause, and it is the part nobody quotes:

Clamping lines parallel to each other within 1° and perpendicular to the direction of force within 1°; the clamp separation must be adjustable to ± 1 mm.
Clamps must hold the strip firmly without slippage or damage. The standard advises cylinder-to-flat or cylinder-to-cylinder clamps, that is a line-contact clamping line, because a defined line fixes the test span exactly and a smooth clamp does not start the break at the jaw.
Force measured to ± 1 % of the true force, elongation to ± 0.1 % of the test length; an extensometer of ISO 9513 class 1 or 0.5 is recommended where the machine's crosshead reading cannot meet that.
A work integrator accurate to ± 1 % if TEA is reported, and a force-elongation plot if the modulus is.
Reject any break within 10 mm of a clamping line. If more than 20 % of the strips in a sample break there, the standard says to check the machine against its apparatus clause and the span and rate clause, because the clamps are damaging the paper.

Serrated faces are the usual cause of the 20 % trigger: the teeth cut the fibres at the clamp line and the strip fails there at a force below its true strength. Flat smooth faces, rubber-faced jaws or a cylindrical upper face against a flat lower face hold a 15 mm paper strip at 60 to 200 N without slip and without cutting it. Serrations are justified only on heavy board and liners where slip in smooth jaws dominates, and then the 10 mm rule still applies.

Conditioning per ISO 187

Standard atmosphere: 23 °C and 50 % RH per ISO 187; the tropical alternative of 27 °C / 65 % is permitted by agreement and must be reported.
Precondition from the dry side. Paper shows moisture hysteresis: a sheet conditioned to 50 % RH from a damp state holds about 0.5 % more moisture than one conditioned from a dry state and tests weaker. ISO 187 therefore requires preconditioning at low humidity before conditioning, and testing in the same atmosphere.
Sampling per ISO 186, which sets how many sheets or reels to draw and how to cut representative test pieces.

Tensile strength of a cellulose paper changes by roughly 1 to 2 % per 1 % RH around the standard atmosphere, so a lab drifting between 45 and 55 % RH already has a 10 % spread hidden in its results. A humidity-controlled room or an environmental chamber around the grips is part of the method, not an accessory.

Step-by-Step Procedure

Sample per ISO 186, precondition from the dry side, condition at 23 °C / 50 % RH, and determine grammage per ISO 536 (and thickness per ISO 534 if modulus is needed).
Cut at least 10 MD and 10 CD strips 15 ± 0.1 mm wide and about 250 mm long with a strip cutter; discard any with nicks or ragged edges.
Set the clamp separation to 180 ± 1 mm, check the clamping lines are parallel, and set 20 mm/min. Choose a load cell so breaks fall in the calibrated range (a 100 or 200 N cell for printing papers, 500 N to 1 kN for board).
Zero force and elongation. Clamp the strip squarely across its full width in the upper clamp, let it hang straight, remove slack without significant stress, and close the lower clamp.
Start the test and record force and elongation continuously; the integrator records the work to maximum force.
Note the maximum force, the elongation at rupture and the work. If the break is within 10 mm of either clamping line, reject the result and record it.
Repeat until 10 valid results per direction are in hand. If more than 20 % of strips broke at the clamps, stop and check clamp faces, alignment and span before continuing.
Calculate tensile strength, tensile index, strain at break, TEA, TEA index and modulus as required; report MD and CD separately with means, the number of rejected breaks, the atmosphere and the edition.

Formulas and a Worked Example

Tensile strength σT (kN/m) = F / w, with F the mean maximum force in N and w the strip width in mm (N/mm equals kN/m).
Tensile index (Nm/g) = σT × 1000 / g, with g the grammage in g/m².
Strain at break (%) = Δl / l0 × 100, with Δl the elongation at rupture and l0 the 180 mm test length.
TEA (J/m²) = W / (l0 × w), with W the work to maximum force in J and the test area in m²; for a 15 mm strip on 180 mm the area is 0.0027 m², so TEA = W(J) × 370.4, or W(mJ) × 0.3704.
TEA index (J/g) = TEA / g.
Modulus of elasticity E (MPa) = (ΔF/Δl)max × l0 / (w × t), with the maximum slope in N/mm, l0 and w in mm and thickness t in mm.
Breaking length (km), used by TAPPI and ASTM rather than ISO: ≈ tensile index / 9.81, or 102 × σT / g.

Worked example: 80 g/m² copy paper, 15.0 mm strips, 180 mm span, 20 mm/min, machine direction. Mean maximum force 60.0 N, elongation at rupture 3.6 mm, work to maximum force 0.080 J, thickness 0.100 mm, maximum slope 25.0 N/mm. Tensile strength = 60.0 / 15.0 = 4.0 kN/m. Tensile index = 4.0 × 1000 / 80 = 50 Nm/g. Strain at break = 3.6 / 180 × 100 = 2.0 %. TEA = 0.080 / (0.180 × 0.015) = 0.080 / 0.0027 = 29.6 J/m². TEA index = 29.6 / 80 = 0.37 J/g. Modulus = 25.0 × 180 / (15.0 × 0.100) = 4,500 / 1.5 = 3,000 MPa. Breaking length = 50 / 9.81 = 5.1 km. The break came at 3.6 mm of travel, 11 s after the start at 20 mm/min; 10 MD and 10 CD strips are about 4 minutes of testing plus loading.

Unit conversions: 1 lbf/in = 0.175 kN/m; 1 kgf/15 mm = 0.654 kN/m; 1 kgf·m/m² = 9.807 J/m²; tensile index in Nm/g × 0.102 = breaking length in km.

Common Errors and Their Size

Serrated jaws on printing paper. Jaw breaks read 5 to 15 % low and inflate the CV; once more than 20 % of strips break at the clamp the standard says the machine is at fault, not the paper.
Dividing by thickness instead of span. Strain is elongation over the 180 mm test length and TEA is work over test length × width; a published application note divides both by thickness, which multiplies the answers by 1,800.
Forgetting the ×1000 in the index. 4.0 kN/m ÷ 80 g/m² is 50 Nm/g, not 0.05; several lab pages print the formula without the factor.
Mixing Part 2 and Part 3 results. 100 mm/min on 100 mm gives 5 to 15 % higher strength than 20 mm/min on 180 mm; there is no conversion.
Running 25 mm strips. That is T 494 / D828 geometry; the force per width is comparable but the result is not an ISO 1924-2 value and the clamp loads differ.
Conditioning from the wet side. About 0.5 % extra moisture and a few percent lower tensile strength; precondition dry first.
Slack at the start. Elongation measured from a slack strip overstates strain by the slack; remove it without significant stress before zeroing.
Ragged edges. A nick from a dull cutter starts a tear and lowers strength and especially TEA; re-sharpen or replace the blade and reject damaged strips.
Crosshead elongation on a compliant frame. The ± 0.1 % elongation requirement is 0.18 mm on 180 mm; grip and frame compliance at 200 N can exceed that, which is why the standard recommends an extensometer for strain and modulus.

ISO 1924-2 vs ISO 1924-3 vs TAPPI T 494 and ASTM D828

Four methods share the same properties and the same tester and are routinely called equivalent. The differences in rate and span change the numbers, and only the specification can say which applies. The figures below for ASTM D828 and T 494 are the commonly used values; confirm them against the current editions.

ISO 1924-2: 15 mm width, 180 mm span, 20 mm/min (11 %/min), at least 10 per direction, ISO 187 23 °C / 50 %; tensile strength, strain at break, TEA, indices, modulus.
ISO 1924-3: 15 mm width, 100 mm span, 100 mm/min (100 %/min), tensile stiffness added, tighter elongation accuracy; results 5 to 15 % higher than Part 2.
TAPPI T 494: 25 mm width (15 mm when specified), 180 mm span, 25 mm/min (14 %/min), 10 per direction, T 402 23 °C / 50 %; tensile strength, stretch, TEA, tensile stiffness, breaking length, tensile index.
ASTM D828: the same geometry and rate as T 494 on a CRE tester, vertical or horizontal; same property set; excludes combined corrugated board.
ISO 12625-4 (tissue): wider strips and a short span at a faster rate, with 'stretch at maximum force' instead of strain at break; not interchangeable with any of the above.

The practical consequence for a lab serving both markets is a cutter with 15 and 25 mm blades, a span that is set to 180 mm for three of the four methods, and a speed table of 20, 25 and 100 mm/min. One grip set with jaws wider than 25 mm covers everything.

Equipment for ISO 1924-2: Grips, Cutters, Extensometers, Machines

Universal Grip ISO 1924-2 vise grip

Our ISO 1924-2 vise grip (part UGC-ISO1924-2-VG) is a compact screw-action grip for paper and board strips. A T-handle screw closes a moving jaw against a fixed jaw, with interchangeable faces that clamp the strip squarely across its full width without slippage or edge damage. From the data sheet: 1 kN standard capacity with higher on request; stainless steel body and jaw faces; serrated or flat faces, rubber-faced on request; jaw width that covers the standard 15 mm strip with margin; open U-frame so strips load from the front; pin or threaded adapter to suit your frame. Specify strip width, paper grade or grammage, jaw faces and machine connection when ordering. For ISO 1924-2 we recommend the flat or rubber faces: the standard advises smooth line-contact clamping, and serrated faces are the usual cause of breaks within 10 mm of the clamp. Keep serrated faces for heavy board and liner where slip governs. Other vise grips in the range cover 25 mm strips for T 494 and D828.

Pneumatic grips and strip cutters

Pneumatic grips: same clamping force on every strip and a foot-switch cycle time of a second or two, which matters at 20 or more breaks per sample; fit flat or rubber faces.
Strip cutters and the die press: a twin-blade cutter that holds 15 ± 0.1 mm with parallel, clean edges is as important to the result as the grip; a dull blade costs TEA before the strip reaches the machine.

Elongation measurement and machines

Extensometers: the ± 0.1 % elongation requirement (0.18 mm on 180 mm) and the modulus slope are best met with a video extensometer that tracks marks on the strip without touching it; a light clip-on extensometer works on board but adds mass to a paper strip.
Load cells: 100 or 200 N for printing and writing papers (breaks of 30 to 150 N on 15 mm), 500 N for kraft and liner, 1 kN for board; keep breaks between 10 and 90 % of range to hold the ± 1 % force requirement.
Machines: a 2.5 kN benchtop universal testing machine with 20, 25 and 100 mm/min speeds, a work integrator in the software and interchangeable low-force cells covers Parts 2 and 3, T 494 and D828; Mark-10 tensile testers suit a converter's QC bench at 20 mm/min with a 15 mm grip set.
Conditioning: a 23 °C / 50 % RH room per ISO 187, or an environmental chamber with humidity control at the grips.

ISO 1924-2 FAQ

What is ISO 1924-2?

ISO 1924-2 is the international standard for the tensile properties of paper and board by the constant-rate-of-elongation method at 20 mm/min. The current edition is ISO 1924-2:2008; a revision is in draft. It gives tensile strength in kN/m, strain at break, tensile energy absorption and the derived tensile index, TEA index and modulus of elasticity.

What specimen size does ISO 1924-2 use?

Strips 15 mm ± 0.1 mm wide with edges parallel within ± 0.1 mm, clamped at a test span of 180 mm ± 1 mm, so about 250 mm long. At least 10 strips are tested in the machine direction and 10 in the cross direction. There is no 25 mm option; that belongs to TAPPI T 494 and ASTM D828.

What test speed does ISO 1924-2 specify?

(20 ± 5) mm/min on the 180 mm span, about 11 % of the test length per minute. A shorter span is allowed by agreement for high-stretch or small samples, with the rate reset to (10 ± 2.5) % of the test length per minute, so 100 mm runs at 10 mm/min.

What is the difference between ISO 1924-2 and ISO 1924-3?

Part 2 uses a 180 mm span at 20 mm/min; Part 3 uses a 100 mm span at 100 mm/min and adds tensile stiffness. The faster strain rate gives results 5 to 15 % higher, and there is no conversion formula between the two, so a specification must name the part.

What clamps does ISO 1924-2 require?

Clamps that hold the strip firmly without slippage or damage, with clamping lines parallel within 1° and perpendicular to the force within 1°, separation adjustable to ± 1 mm. The standard advises cylinder-to-flat or cylinder-to-cylinder line-contact clamps. Flat or rubber faces suit paper; serrated faces cause jaw breaks.

When is a break rejected in ISO 1924-2?

Any break within 10 mm of a clamping line is rejected and the number is reported. If more than 20 % of the strips in a sample break within 10 mm of the clamps, the machine, clamps, span and rate must be checked, because the clamping is damaging the paper.

How is tensile index calculated?

Tensile index in Nm/g = tensile strength in kN/m × 1000 ÷ grammage in g/m². An 80 g/m² paper with a tensile strength of 4.0 kN/m (60 N on a 15 mm strip) has a tensile index of 50 Nm/g, equivalent to a breaking length of about 5.1 km.

How is tensile energy absorption calculated?

TEA in J/m² = work to maximum force in J ÷ (test length × width in m²). On a 15 mm strip at 180 mm span the area is 0.0027 m², so 0.080 J of work gives 29.6 J/m². TEA index = TEA ÷ grammage, 0.37 J/g for an 80 g/m² sheet.

What conditioning does ISO 1924-2 use?

ISO 187: 23 °C and 50 % RH (27 °C / 65 % as a tropical alternative), with preconditioning from the dry side to avoid moisture hysteresis, and testing in the same atmosphere. Tensile strength changes by roughly 1 to 2 % per 1 % RH, so humidity control is part of the method.

Is ISO 1924-2 the same as TAPPI T 494 or ASTM D828?

No. T 494 and D828 use 25 mm strips (15 mm when specified) on a 180 mm span at 25 mm/min and report stretch, tensile stiffness and breaking length; ISO 1924-2 uses 15 mm strips at 20 mm/min. The span is the same and one grip set serves all three, but the results are not interchangeable.

Does ISO 1924-2 apply to corrugated board and tissue?

It applies to the components of corrugated board, liner and fluting, but not to combined corrugated board, which is tested by edge-crush and box-compression methods. Tissue is tested under ISO 12625-4, laboratory handsheets under ISO 5270 and wet tensile strength under ISO 3781.

What load cell and machine do I need for ISO 1924-2?

Breaks on 15 mm strips run from about 30 N for lightweight papers to several hundred newtons for board, so a 100 or 200 N cell for paper and 500 N to 1 kN for board keeps results in the calibrated range. A 2.5 kN benchtop universal testing machine or a Mark-10 tester with 20 mm/min, a work integrator and a 15 mm grip set with flat faces covers the method.

Need paper tensile grips, strip cutters or a complete CRE system for ISO 1924-2? Contact Universal Grip with your paper or board grades, strip width and machine connection and we will quote the right setup.

Literature

Pricing and Availability

ISO 1924-2 Tensile Properties of Paper and Board (20 mm/min)