Testing standard
Rubber, vulcanized or thermoplastic — Determination of tear strength — Part 1: Trouser, angle and crescent test pieces
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ISO 34-1 measures the tear strength of vulcanised and thermoplastic rubber. A die-cut piece with a slit or razor nick is pulled so an existing tear is driven along it, and the force to propagate that tear divided by the piece thickness is the result, in kilonewtons per metre. Three geometries are covered and each gives its own number.
A die-cut strip of vulcanised or thermoplastic rubber is clamped in two tensile grips and pulled apart at constant jaw separation. The tear starts at a slit or a razor nick already cut into the piece, so the machine is not breaking the rubber but driving an existing tear along it. Force is recorded continuously against time, and the trace is jagged rather than smooth.
The result is tear strength: the force to propagate the tear divided by the test piece thickness, reported in kilonewtons per metre. It is the property that decides whether a seal survives demoulding, whether a hose sleeve resists a nick growing into a split, and how much a tyre or conveyor cover tolerates cuts in service. Compounders use it to judge filler loading and cure state, so it works as a batch-release check and as a formulation input rather than as a service-life prediction.
The trace is jagged, not smooth, and that is the signal rather than noise — a tear advances in steps as it crosses filler and crosslink structure. Averaging it aggressively in software throws away what the method is measuring.
Ts = F / d
Reported in kilonewtons per metre. Force per unit THICKNESS, because a tear travels along a path rather than failing across a section — there is no area to divide by.
Flat vice-action faces hold a die-cut piece — or the two legs of a trouser piece — squarely and at low force, which is what a tear test needs rather than the self-tightening action a tensile dumb-bell wants.
SpecificationsThis is a low-force test. With the preferred 2.0 mm sheet, ordinary rubbers tear at roughly 10 N to 250 N and only the toughest reinforced grades approach 500 N, so a frame is chosen for fine resolution at the low end rather than for capacity. The force system must meet ISO 5893 Class 1, and it must be low in inertia: tear peaks arrive fast, and a heavy load train lags them and reads low.
Speed is fixed by geometry — 100 ± 10 mm/min jaw separation for the trouser piece, 500 ± 50 mm/min for the angle and crescent pieces. No strain or elongation measurement is required and no extensometer is needed. The demand is travel instead: the trouser tear must be followed along the whole remaining ligament while soft rubbers add substantial leg extension, and ISO 5893 warns that highly extensible materials can need over a metre of traverse.
Grips must tighten as tension rises and press uniformly across the widened end, with positioning that puts each piece symmetrically on the machine axis; wedge or pneumatic self-closing types are named for flexible materials. No dedicated tear fixture is called for — the geometry lives in the cutting die and the nick cutter. Ambient testing suffices unless another ISO 23529 temperature is chosen, which then needs a chamber.
Knotty tear is the common one: the tear advances in stick-slip jumps and the trace turns saw-toothed, so a median force to ISO 6133 must be read rather than a single peak. Leg extension in soft compounds eats crosshead travel and can end the test before the ligament is consumed. An inconsistent nick depth moves the tear initiation point and scatters results between operators. Grip slippage lets a leg creep, flattening the trace and understating the force.
| ISO 34-1 | ASTM D624 | |
|---|---|---|
| Geometries | Trouser, angle, crescent | Five dies: A, B, C, T and CP |
| Preferred thickness | 2.0 mm | Nominally 2.3 mm for Die C |
| Result units | kN/m | kN/m or N/mm |
| Nick | Guided razor cutter | Controlled depth, fresh blade |
| Comparable to the other | No | No |
The principle is shared and the numbers are not. Pieces and rates differ, and tear strength is a property of the compound and the geometry together — so a figure from one document cannot be checked against a specification written for the other.
It is the international standard for tear strength of vulcanised and thermoplastic rubber. A die-cut piece carrying a slit or razor nick is pulled so an existing tear propagates along it, and the force to drive that tear divided by the piece thickness gives the result in kilonewtons per metre.
Where the tear starts and what force is read. The trouser piece is slit along its length and its legs clamped separately, so the tear is already running and a propagation force is read from a plateau. The angle piece tears from an apex and the crescent from a nick on its concave edge, both giving a peak. Each geometry produces its own number and they do not convert.
Because the specimen does not fail across a cross-section. A tear runs along a path, and the only dimension resisting it is the thickness it has to travel through — so the result is a force per unit thickness rather than a stress. That is also why the thickness is measured on the piece itself, at the tear path.
Because a tear advances in steps rather than smoothly, as it crosses filler particles and variations in crosslink density. That roughness is the measurement rather than noise, so heavy smoothing in software rounds off the peaks and under-reports the result — an error that is systematic and always in the same direction.
They share the principle and differ in the detail. ISO 34-1 defines trouser, angle and crescent pieces at a preferred 2.0 mm thickness; D624 defines five dies including a moulded constrained-path type. Rates differ too. Since tear strength depends on the geometry as much as on the compound, results from one cannot be checked against a specification written for the other.
Because its depth decides where the tear begins and how much of the piece resists it. A nick cut by eye varies from piece to piece, and that variation appears directly in the result as scatter that looks like compound variability. The guided razor cutter is what makes the starting condition repeatable.
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 | A low-force test. With the preferred 2.0 mm sheet, ordinary rubbers tear at roughly 10 N to 250 N and only the toughest reinforced or high-tear grades approach 500 N, so a frame is chosen for fine low-end force resolution, a low-inertia load cell and long crosshead travel rather than for capacity. | 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 5893 Class 1 | ISO 7500-1 Class 0.5, verified to ASTM E4, DIN 51221 and BS 1610 |
| Gripping | Self-tightening tensile grips with symmetric positioning on the machine axis, trouser legs one per grip; die-cut trouser, angle or crescent test pieces plus a guided razor nick cutter | Our vice-action grips or self-tightening serrated wedge grips, with V-jaws for round specimens, built to the specimen |
| Environment | Ambient — sheets conditioned at least 3 h and tested at a standard laboratory temperature of 23 ± 2 °C or 27 ± 2 °C per ISO 23529; a chamber only where another temperature from ISO 23529 is selected | 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.
