Testing standard
Resistance welding — Destructive testing of welds — Specimen dimensions and procedure for tensile shear testing resistance spot and embossed projection welds
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ISO 14273 pulls a lap joint containing a single resistance spot weld along the plane of the sheets and reports the maximum force the joint carried. It is a force, not a stress, and it is always reported with the failure mode: a button pull-out means the nugget beat the sheet, an interfacial break means it did not. The current edition is ISO 14273:2016.
From the test method to your testing system
Explore the DAK machines already listed for ISO 14273, then review the grips, measurement and setup requirements below.
Universal Testing MachineSeries 7200Explore the machine →
Universal Testing MachineSeries 9000Explore the machine →01Understand the method
Two overlapping sheets joined by a single resistance spot weld are pulled apart along the plane of the sheets. Each sheet is gripped at its free end, packing shims are fitted so the line of pull passes as nearly as possible through the weld, and the grips separate until the joint fails. The maximum force recorded is the tensile shear force. It is the commonest destructive weld test in a press shop because it is the simplest that produces a number.
The result is a force, not a stress. There is no meaningful area to divide by: the nugget is a rough disc whose diameter is unknown until the specimen is sectioned, and the load path through a lap joint is not pure shear anyway.
That force is used two ways. Against an acceptance value in a welding procedure specification it says whether the joint passes. Plotted against welding current, with weld time and electrode force fixed, it maps the usable current range — the window between too little heat for a sound nugget and enough for expulsion. Drawing that window is the goal of most spot-welding development. Failure mode carries as much information: a button pull-out means a nugget stronger than the sheet, while an interfacial failure points at an undersized or defective nugget even when the force looks acceptable.
02Prepare the specimen and test settings
The tabulated dimensions exist to force failure at the weld. A specimen that is too narrow yields in the parent sheet and measures the steel instead of the joint.
Dissimilar-thickness and dissimilar-material joints are common in a modern body shop and are outside the tabulated geometry. Agree the specimen with the customer before cutting, and record what was agreed, because two laboratories will otherwise choose differently and their numbers will not compare.
03Build the test setup on a DAK machine
A single spot weld in thin automotive sheet fails between a few kilonewtons and roughly 30 kN; thicker sheet takes more. A 50 to 100 kN frame with clean resolution at the bottom of its range covers most of this work, with force to ISO 7500-1 Class 1.
The method sets no rate of traverse. What it controls is the specimen, the load path and the measurement: the tabulated geometry above, shim plates as thick as the sheet wherever it is under 3 mm or the two thicknesses differ by more than 1,4 to 1, force to ISO 7500-1, and room temperature. The rate is the laboratory's to fix and record — published work to this method runs between 1 mm/min and 10 mm/min — and a current series only compares if the rate held within it.
Grips must hold a flat, coated strip without slipping or bending it: serrated hydraulic wedge or vice-action faces, wide enough for the full specimen. The critical detail is the packing — without shims the specimen rotates and the test measures a peel, not a shear. No extensometer is needed, but the data rate has to catch a peak that arrives abruptly, because a spot weld does not neck.
Flat, serrated faces wide enough to take the full specimen width, closing on a coated strip without slipping. Hydraulic closure keeps the clamping force the same from specimen to specimen, which matters across a weld-current series where the only variable is meant to be the current.
Specifications
Where the specimen is wide and the force is modest, a 100 mm vice-action grip takes the whole width in one clamped face. Packing shims still have to be fitted; the grip does not remove the offset.
SpecificationsA load cell sized for the joint rather than the frame. Thin-sheet spot welds fail in single-digit kilonewtons, and a cell chosen for a 600 kN frame throws away the resolution the peak needs.
SpecificationsDak 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 few kN to roughly 30 kN on thin automotive sheet; higher towards the 10 mm end of the thickness range | 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 7500-1 Class 1 | ISO 7500-1 Class 0.5 — a class tighter than the method asks |
| Gripping | Flat serrated grips with packing shims of the sheet thickness in both jaws | Our self-tightening serrated wedge grips, with V-jaws for round specimens or vice-action grips, built to the specimen |
| Environment | Ambient laboratory conditions; no conditioning atmosphere is specified for the joint | 3009 series chambers, −150 °C to +400 °C — temperature only |
04Run the test
The shims are not optional and they are not a convenience. Without them the two sheets are offset by their own thickness, the specimen rotates as load builds, and the joint is peeled open rather than sheared. The number that comes out is low, repeatable, and wrong.
05Calculate, report and interpret
The maximum force recorded before the joint fails
Reported as a force. No division by area is performed.
Nugget area is unknown until the weld is destroyed
The nugget is a rough disc whose diameter is only known after sectioning or peeling, and a lap joint is not in pure shear anyway. A quoted MPa figure for a spot weld is an invention.
Tensile shear force plotted against welding current
Weld time and electrode force are held constant while current is stepped. The width of that window is what most spot-welding development is trying to widen.
Omitted or wrong-thickness packing shims are the commonest error, and they lower the recorded force in a way that looks like a welding problem rather than a fixturing one. Misaligned grips do the same more subtly. Specimens cut with a torch or abrasive wheel change the metallurgy beside the nugget. Recording only the force, without the failure mode, throws away half the test. And letting the rate drift between batches, when the method leaves it open, quietly makes a series uncomparable.
06Compare methods and find answers
They load the same nugget in three different directions and answer three different questions. A specification that names one is not satisfied by another.
| Tensile shear (ISO 14273) | Cross tension (ISO 14272) | Mechanised peel (ISO 14270) | |
|---|---|---|---|
| Load direction | Along the plane of the sheets | Through the sheet thickness | Progressive peel from one edge |
| Sheet thickness covered | 0.5 mm to 10 mm | 0.5 mm to 3 mm | 0.5 mm to 3 mm |
| Typical use | Process setup and routine acceptance | Ductility and crash-relevant behaviour | Nugget quality and coating effects |
| Fixture | Flat grips with packing shims | A dedicated cross-tension jig | A dedicated peel jig |
| Result | Maximum force plus failure mode | Maximum force plus failure mode | Peel force plus failure mode |
A joint can pass in tensile shear and fail in cross tension. Shear loads the nugget in its strongest direction; cross tension opens it. Where crash performance matters, the shear figure alone is not evidence.
ISO 14273 is the international method for tensile shear testing of resistance spot and embossed projection welds. A lap joint containing one weld is pulled along the plane of the sheets until it fails, and the maximum force is reported together with the failure mode. The current edition is ISO 14273:2016, which superseded ISO 14273:2000 and narrowed the scope by dropping seam welds from the title.
Because there is no area to divide by. The weld nugget is a rough disc whose diameter is not known until the specimen is sectioned or peeled apart, and the stress state in a lap joint is a mixture of shear, tension and bending rather than pure shear. Every acceptance criterion for spot welds is written as a force for this reason, and a shear strength in MPa quoted for a spot weld has been invented somewhere along the way.
They put the two sheets in line. Without them the sheet clamped in the upper grip and the sheet clamped in the lower grip are offset by their own thickness, so the specimen rotates as load builds and the weld is progressively peeled rather than sheared. The result is low and repeatable, which is what makes it dangerous: it looks like a welding problem and it is a fixturing one. The shims are the same thickness as the sheet and go in both grips.
As much as the force. A plug or button pull-out, where the nugget tears a hole out of one sheet and stays attached to the other, means the weld is stronger than the parent metal around it. An interfacial failure, where the joint parts flat across the weld face, means the nugget was undersized or defective even if the force looked acceptable. Reporting force without failure mode discards half the test.
Direction. Tensile shear loads the nugget along the plane of the sheets, which is its strongest direction, while cross tension pulls the sheets apart through the thickness and opens the weld. A joint can pass in shear and fail in cross tension, which is why crash-relevant work runs both. ISO 14272 also covers a narrower thickness range, 0.5 mm to 3 mm against 0.5 mm to 10 mm here, and needs a dedicated jig rather than flat grips.
A tensile frame of 50 to 100 kN with force accuracy to ISO 7500-1 Class 1 covers most automotive sheet work, and clean resolution at the bottom of the range matters more than headline capacity because thin-sheet welds fail in single-digit kilonewtons. Grips must hold a flat coated strip without slipping, and the data rate has to be high enough to catch an abrupt peak, because a spot weld does not neck before it goes. The method does not set a rate of traverse — it fixes the specimen, the shims, the force accuracy and room temperature — so pick a rate in the 1 to 10 mm/min range the published work uses, and hold it.
No. The coating is part of the joint. Zinc, zinc-iron and aluminium-silicon coatings change the contact resistance at the faying surface and therefore change how the nugget grows, which is exactly what the test is measuring. A specimen stripped back to bare steel no longer represents anything the production line makes.
The scope is any metallic material, so aluminium is covered, and in practice aluminium spot welds are tested this way routinely. Dissimilar-thickness and dissimilar-material stack-ups are a different matter: the tabulated specimen geometry assumes two sheets of the same thickness, so the geometry has to be agreed between the parties and recorded in the report. Without that agreement two laboratories will choose differently and their figures will not compare.
Discuss your specimen, test requirements and reporting needs with DAK engineering.
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.
