ISO 1974

What the test does

A stack of paper is cut, slit and torn by a falling pendulum, and the energy the pendulum loses is the result. It is among the fastest tests in a paper laboratory and one of the oldest; the apparatus has barely changed in principle since Elmendorf designed it.

Specimens are cut 63 mm × 76 mm and a 20 mm slit is made in the centre of each with a clean blade, which starts the tear rather than leaving the paper to find its own starting point. Four superimposed sheets are torn together as one specimen. Fewer or more may be used where the paper demands it, provided the deviation is stated in the report — the number of plies changes the reading, so it is part of the result rather than a detail of how it was obtained.

The pendulum is released, tears through the remaining width, and swings on. What it measures is out-of-plane tearing resistance: the sheet is torn apart through its thickness, not pulled along its plane. The pendulum capacity is chosen so the reading falls between 20 % and 80 % of the scale, which is where the instrument is linear.

What it measures, and why it matters

Tearing resistance decides whether a web survives a machine. Tensile strength tells you what a sheet withstands pulled evenly; tear tells you what happens once a flaw exists, which on a running machine it eventually always does. A nick at the edge of a web under tension is the start of either nothing or a break, and tear decides which.

The measurement is always made in both machine and cross directions, and the ratio between them is as informative as either figure. Paper is anisotropic because the fibres align with the flow on the wire, so a sheet tears far more readily along the machine direction than across it. A ratio that has drifted from its usual value says the forming section has changed even when both absolute figures still sit inside specification.

Two exclusions matter. The method does not apply to corrugated fibreboard, though it may be used on its components. And it is not suitable for cross-direction tearing resistance of highly directional paper or board, where the tear runs away along the fibres and the number returned is not a property of the material.

Specimen

Cut in both directions, stacked, and slit — the slit is what starts the tear rather than leaving the paper to find its own beginning.

Size

63 mm × 76 mmCut in both machine and cross direction so both can be reported. A single figure without its direction is not a measurement.

Plies

Four superimposed sheetsFewer or more may be used where the paper demands it, provided the deviation is stated in the report. A two-ply and a four-ply result are different numbers for the same paper.

Slit

20 mm, central, clean bladeA ragged or crushed slit end gives the tear a head start nobody has recorded, and biases the result low with nothing on the instrument to show why.

Conditioning

Standard atmosphere for paper testingTear resistance moves with moisture content, so an unconditioned sheet is not comparable with anything.

Test speed

There is no crosshead and no rate to set: the pendulum is released and falls under gravity, and the result is the potential energy it loses tearing the stack. What the operator controls instead is the tear length, the pendulum capacity and where the reading lands on the scale.

Rate

None to set — gravity-driven pendulumUnlike a trouser-tear test on a crosshead, the tearing speed is a consequence of the pendulum rather than a parameter. Two laboratories running the same instrument tear at the same rate because the apparatus is specified, not because a rate was dialled in.

Tear length

43 mmDakThe distance the tear actually runs: 63 mm of specimen in the direction tested, less the 20 mm starting slit. It is fixed by the specimen geometry rather than chosen.

Pendulum capacity

Interchangeable weights, commonly 8 000 mN to 64 000 mNDakThis is the operator's real control over the measurement. Instrument makers supply the range; the standard requires only that the capacity chosen puts the reading in the linear part of the scale.

Target reading

Between 20 % and 80 % of scaleWhere the instrument is linear. A pendulum too heavy gives a small deflection where resolution is worst; too light and it stalls before completing the tear.

How the test runs

1. 01Condition the paper in the standard atmosphere for paper testing.
2. 02Cut specimens 63 mm × 76 mm in both machine and cross direction.
3. 03Stack four sheets and clamp them square and flat without crushing.
4. 04Cut a clean 20 mm slit centrally through the stack.
5. 05Select a pendulum capacity that will put the reading between 20 % and 80 % of scale.
6. 06Release the pendulum and read the tearing resistance.
7. 07Report machine and cross direction separately, with the ply count used.

What travels with an ISO 1974 result

Two of these change the number, so a result without them cannot be compared.

• The direction — machine or cross. Values for one sheet can differ severalfold.
• The number of plies, if it was not four.
• The pendulum capacity used, and that the reading fell inside the 20 % to 80 % band.
• The conditioning atmosphere.
• The MD to CD ratio, which tracks fibre alignment and often moves before either figure leaves specification.

What the machine must be capable of

An Elmendorf pendulum tear tester with interchangeable weights, so a capacity can be chosen that puts the reading in the 20 % to 80 % band. A clamp holding all four plies square and flat without crushing them, a blade producing a clean 20 mm slit, and a calibrated scale or transducer.

The instrument must be level and its pendulum free. Friction in the pivot subtracts from the energy the paper absorbed and adds it to the recorded tear resistance — an error that is systematic, always in the same direction, and invisible without a routine zero check.

What goes wrong in practice

Reading outside the 20 % to 80 % band is the most common. A pendulum too heavy for the paper gives a small deflection at the bottom of a scale where resolution is worst; too light and it stalls.

A blunt or dirty slitting blade is the second, and it always biases low.

Testing the wrong number of plies without saying so is the third. Four is the default and the report has to state any departure, because a two-ply and a four-ply result are different numbers for the same paper.

Finally, quoting a single tear figure without its direction. Machine and cross direction values for the same sheet can differ severalfold, so a figure without a direction beside it is not a measurement.

What ISO 1974 does not cover

Two exclusions, and both are the kind that produce a plausible number rather than an obvious error.

Both exclusions still return a reading. Nothing on the instrument tells you the number is meaningless.

Questions we are asked about this test

Related and equivalent standards

TAPPI T 414 is the closest counterpart and uses the same Elmendorf principle, so results are comparable in trend but not automatically interchangeable in figure. ISO 1974 sits beside the other paper strength methods — tensile to ISO 1924-2 and burst to ISO 2758 — which together describe how a sheet fails in the three ways a converting line can break it.