Testing standard
Leather — Physical and mechanical tests — Measurement of stitch tear resistance
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ISO 23910 measures the stitch tear resistance of leather: a mandrel is passed through a slit cut in the test piece, and the leather is torn off it while the maximum force in newtons is recorded. It applies to all leathers and is particularly suited to leather over 1,2 mm thick. The current edition is ISO 23910:2019, published as IULTCS/IUP 44.
A slit is cut in a rectangular piece of leather, a metal mandrel is passed through the slit, and the leather is torn off the mandrel. The mandrel sits between the arms of a metal test piece holder gripped in the upper jaw; the free end of the leather is clamped in the lower jaw. The machine runs until the test piece tears apart, and the maximum force in newtons is recorded. The slit is not cut separately — the press knife that cuts the outline cuts it in the same operation, and a subsequent cut with a knife or similar tool is not permitted, because a slit finished by hand has a different tip and tears at a different force.
How much force a stitch hole in leather will take before the leather between the hole and the edge gives way. That is the failure mode behind a seam pulling open on a shoe upper, a car seat or an upholstered arm — the thread holds, the stitching holds, and the leather tears from hole to hole until the seam unzips. Tensile strength does not predict it and neither does tear load, because both are measured on uncut material away from a concentrated bearing point. The standard applies to all leathers but is particularly suited to leather over 1,2 mm thick, where the property drives seam design directly.
The slit is cut by the same knife that cuts the outline, in one operation. That is a requirement, not a convenience.
Thickness is not a formality here. The result is a force, not a stress, so it cannot be interpreted without knowing how thick the leather was — and the report is required to carry it.
The maximum force recorded while the test piece tears apart, in newtons
Recorded in newtons for each test piece; the directional means go into the report to the nearest 0,1 N. Nothing is divided by a thickness or an area — the thickness is reported alongside instead.
Arithmetic mean of the three pieces cut with the longer edge parallel to the backbone
Arithmetic mean of the three pieces cut with the longer edge perpendicular to the backbone
The two directions are reported separately. Leather fibre structure runs with the backbone, so the two means are not the same number.
The arithmetic mean of the two directional means
Reported only if the customer or the specification requires it. It is an optional figure, not the result.
The standard specifies jaws at least 25 mm long in the direction of load, applying constant clamping by mechanical or pneumatic means, with faces that do not let the specimen slip at maximum load. Pneumatic vice action gives that constant pressure on a material whose thickness varies across a single piece. The mandrel and the two-armed test piece holder are a purpose-made rig, drawn to dimension in the standard.
SpecificationsStitch tear means are reported to the nearest 0,1 N, so the cell has to resolve at that level. A cell chosen for the frame rather than for the leather cannot.
SpecificationsNot much force, but steady clamping and a slow, controlled crosshead. The jaws separate at 100 mm/min ± 20 mm/min, and the force-measuring system must meet class 2 of ISO 7500-1:2018. The jaws themselves are specified: a minimum length of 25 mm in the direction of the applied load, constant clamping applied by mechanical or pneumatic means, with face texture and design such that the specimen does not slip at the maximum load reached in the test. The rest of the apparatus is a purpose-made rig — the mandrel and the two-armed test piece holder are drawn to dimension in the standard.
Tidying the slit with a scalpel after the press knife, which the standard prohibits and which changes the result. Letting a thick, greasy specimen slip in the jaw and reading the slip as a tear. Reporting a single mean: the report has to carry the mean parallel to the backbone and the mean perpendicular to it separately, and the overall average only if the customer or specification asks for it. Omitting the thickness, without which the figure cannot be interpreted, since a thicker leather tears at a higher force for reasons that have nothing to do with its quality. And converting the result into a stress, which the method does not do — it is a force in newtons, with the reported means quoted to the nearest 0,1 N.
| Stitch tear (ISO 23910) | Tear load (ISO 3377-1 / -2) | Tensile strength (ISO 3376) | |
|---|---|---|---|
| Loaded through | A mandrel in a slit, as a stitch would load it | A cut edge or a double-edge tongue | The whole cross-section, in tension |
| Predicts | Whether a seam unzips | How a cut or nick propagates | How much load the leather carries |
| Result | Force in newtons | Force in newtons | Strength and elongation |
| Speed | 100 mm/min ± 20 mm/min | As specified in that method | As specified in that method |
These are three different failure modes and a good result in one does not imply a good result in another. A seam pulling open is a stitch tear failure, and tensile strength does not predict it.
ISO 23910 specifies a method for determining the stitch tear resistance of leather. A slit is cut in a test piece, a metal mandrel is passed through it, and the leather is torn off the mandrel while the maximum force is recorded in newtons. The current edition is ISO 23910:2019, the third, which also carries the designation IULTCS/IUP 44.
Whether a seam will unzip. When a stitched seam is loaded, each stitch bears on the leather between its hole and the edge. If that leather gives way the thread is still intact and the stitching is still sound, but the seam opens as the tear runs from hole to hole. Tensile strength does not predict this and neither does tear load, because both are measured on material away from a concentrated bearing point.
Because the tip of the slit is where the tear starts, and its geometry sets the force. The press knife cuts the outline and the slit in one operation with all its cutting edges in the same plane, giving an identical slit every time. The standard states that a subsequent cut with a knife or similar tool is not permitted. A hand-finished slit has a different tip radius and a different local damage state, and it tears at a different force.
Because leather is not isotropic. Its fibre structure runs with the backbone, so a piece cut parallel to the backbone and one cut perpendicular to it do not tear at the same load. The method takes three pieces in each direction and requires the mean for each direction in the report. The average of the two is reported only if the customer or the specification asks for it.
It can be used on all leathers, and is particularly suitable for leathers over 1,2 mm in thickness. That is where the property drives design decisions — upholstery, footwear uppers and heavy goods, all of which are stitched through material thick enough for the stitch to bear on a real depth of leather.
Because the loaded area is not a defined cross-section. The mandrel bears on the slit over a contact that changes as the tear runs, so a stress computed from thickness times some assumed width would be a number without a defined geometry behind it. The method records the maximum force in newtons, reports the directional means to the nearest 0,1 N, and requires the thickness to be reported alongside, so the reader can interpret one against the other.
A tensile frame with a force range appropriate to the specimen, force measurement to class 2 of ISO 7500-1:2018, and a uniform jaw separation speed of 100 mm/min ± 20 mm/min. The jaws must be at least 25 mm long in the direction of the applied load and apply constant clamping by mechanical or pneumatic means, with faces textured so that the specimen does not slip at the maximum load reached in the test.
Very little, and only in one place. The third edition cancels and replaces ISO 23910:2017, which the ISO catalogue now records as withdrawn, and the stated change is that the wording of the sampling and conditioning clauses was modified to remove a possible misunderstanding about how samples are conditioned. The apparatus, the test piece and the procedure are unchanged.
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 | Low — the result is a force in newtons, with the directional means reported to the nearest 0,1 N | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | Class 2 of ISO 7500-1:2018 | ISO 7500-1 Class 0.5 — a class tighter than the method asks |
| Gripping | A purpose-made rig: a metal mandrel and a two-armed metal test piece holder, both drawn to dimension in the standard | Wedge, vice-action, pneumatic and hydraulic grips, built to the specimen |
| Environment | The standard atmosphere of ISO 2419, for conditioning and for testing | 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.
