TJ-144
Heavy Duty Hydraulic Grips
Heavy duty hydraulic wedge grips hold a constant clamping force on a thick welded coupon as it necks, which a mechanical wedge does not always manage at these loads.
SpecificationsTesting standard
ISO 9018
Destructive tests on welds in metallic materials — Tensile test on cruciform and lapped joints
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ISO 9018 specifies test pieces and the procedure for tensile tests on welded cruciform and lapped joints with transverse stressed fillet welds, determining the tensile strength and the location of the fracture. It states that evaluation of the results is not included in the standard.
At a glance
- Test type
- Tensile — the specimen is pulled apart
- Published by
- ISO
- Edition
- ISO 9018:2015
- Material
- Metals, alloys & welds
- Runs on
- Series 7200 and Series 9000
What the test does
Cruciform or lapped test pieces are welded using the procedure being qualified, the fillet weld throats achieved are measured, and specimens of the required width are cut. The specimen is gripped so the load path crosses the transverse fillet welds and pulled at the specified rate to failure. Two things are reported: the tensile strength, calculated on the area appropriate to the joint geometry, and the location of the fracture — through the weld throat, along the fusion boundary, or through the plate.
What it measures, and why it matters
Whether transversely loaded fillet welds carry the load, and where they give way. The interpretive difficulty, and the reason this method deserves its own standard, is that a fillet weld's load-carrying section cannot be seen once the joint is made. A full-penetration butt weld transfers load through the full plate section, which is measurable at any time. A fillet weld transfers it across a throat — the altitude of the weld triangle rather than a leg length — and a weld that looks generous can have a modest throat if it is concave. The strength depends on what was achieved, not on what was drawn.
Fillet welds under transverse load
A butt weld carries load through its full section. A fillet weld carries it through a throat that nobody can see once the joint is made.
- Joint types
- Cruciform and lapped
- Welds
- Transverse stressed fillet weldsThe load crosses the weld rather than running along it.
- Applies to
- Plates, sheets, extruded bars and other solid sectionsThe standard uses plate as a general term for all of these.
- Reported
- Tensile strength and fracture location
- Evaluation of results
- Explicitly not included in the standardNo acceptance criteria. Those come from the application standard or the contract.
- Measure the actual throat, not the specified one
- DakFillet weld throats vary with fit-up and technique, and the strength depends on what was achieved rather than what was drawn.
Fracture location matters as much as in a butt joint. Failure through the throat is a weld result; failure through the plate means the welds were stronger than the material they joined.
Test speed
- Rate
- Per the standard's requirements
- Reported
- Tensile strength and fracture location
- Acceptance
- From the application standard, not from here
- Section a failed joint to see the root
- DakLack of root penetration in a fillet weld is invisible from outside and is a common cause of low throat failures.
Calculations
Tensile strength of the joint—
Maximum force divided by the relevant cross-sectional area
- area
- as defined for the joint geometry being tested
Which area applies depends on the joint type, so the basis has to be stated with the value.
Why the throat governs—
A fillet weld transfers load across its throat, not across the plate thickness
The throat is a triangle's altitude, not a leg length, so a weld that looks generous can have a modest throat if it is concave.
Acceptance—
Not defined in ISO 9018
Stated in the standard's own scope. A report that implies a pass or fail without naming its source is overreaching.
How the test runs
- 01Prepare cruciform or lapped test pieces to the specified geometry.
- 02Weld them using the procedure being qualified, recording all parameters.
- 03Measure the actual fillet weld throats achieved.
- 04Cut specimens to the required width.
- 05Fit wedge grips sized for the plate thickness.
- 06Align the specimen so the load path is as intended for the joint type.
- 07Load at the specified rate to failure.
- 08Record the maximum force.
- 09Identify the fracture location — through the throat, the fusion boundary, or the plate.
- 10Section a failed joint where root penetration is in question.
- 11Compare against the acceptance criteria in the application standard, naming it.
Grips and fixtures for this method
Self-tighteningTJ-15
Universal Parallel Wedge Grips
Universal parallel wedge grips with flat inserts, where the plate thickness and failure load sit within their range.
SpecificationsWhat the report has to contain
- Reference to ISO 9018 and the edition
- Parent material and welding procedure identification
- Joint type — cruciform or lapped
- Test piece geometry and specimen width
- Specified and measured fillet weld throats
- Rate of testing
- Maximum force and the calculated strength, with the area basis stated
- Fracture location, classified
- Any evidence of lack of root penetration
- The acceptance criteria applied and the standard they came from
What the machine must be capable of
Substantial force — a cruciform coupon in structural plate commonly needs a hundred kilonewtons or more — with wedge grips sized for the plate thickness and enough daylight for the assembled joint. Alignment good enough that the load is genuinely axial matters here more than on a plain coupon, because the geometry already carries an offset and a bending component added by the fixture will move the failure to whichever weld happens to be on the tension side.
What goes wrong in practice
Reporting a pass or fail as though the standard supplied one, when it explicitly does not — the acceptance criteria come from the application standard or the contract and their source belongs in the report. Reporting a strength without the fracture location, which discards the diagnostic half of the result. Assuming the specified throat is the throat achieved. And failing to section a low-failing joint, which is usually where an unfused root — invisible from outside — turns out to explain everything.
ISO 9018 or ISO 4136
| ISO 9018 | ISO 4136 | |
|---|---|---|
| Joint | Cruciform and lapped, fillet welded | Butt joint, full penetration |
| Load path | Across the fillet throats | Through the full weld section |
| Acceptance criteria | Not given in the standard | Usually the parent minimum |
| Both report | Strength and fracture location | Strength and fracture location |
Two joint families with the same reporting discipline. The fillet case is the harder one to interpret, because the load-carrying section is a throat that cannot be seen after welding and often differs from what was specified.
Questions we are asked about this test
What is ISO 9018?
It is the ISO tensile test for welded cruciform and lapped joints with transverse stressed fillet welds. It specifies the test pieces, the specimens and the procedure, and it determines the tensile strength and the location of the fracture. It applies to plates, sheets, extruded bars and other solid sections. The current edition is ISO 9018:2015.
Why does it give no acceptance criteria?
Because the standard says so in its own scope: information concerning the evaluation of test results is not included. It is a method, not a specification. The pass or fail comes from the application standard, the design code or the contract, and a test report that implies a verdict without naming where the criterion came from is claiming more authority than the method has.
Why are fillet welds harder to interpret than butt welds?
Because the load-carrying section cannot be seen. A full-penetration butt weld transfers load through the full plate section, which is measurable. A fillet weld transfers it across its throat — the altitude of the weld triangle, not a leg length — and once the joint is made that dimension is hidden. A weld that looks generous can have a modest throat if it is concave, and a specified throat is not necessarily the throat achieved.
What does the fracture location tell you?
The same thing it does in a butt joint. Failure through the throat means the welds were the limiting element. Failure through the plate means they were stronger than the material they joined, which is generally the outcome a procedure is qualified to produce. Failure along the fusion boundary points at penetration or technique rather than at weld metal strength.
Why section a failed joint?
To see the root. Lack of penetration at the root of a fillet weld is entirely invisible from outside — the weld looks complete, the profile looks correct — and it reduces the effective throat directly. A joint that failed at a low load through the throat, sectioned, will often show an unfused root that explains the result and points at fit-up or technique rather than at the consumable.
What is a cruciform joint?
Two plates welded to opposite faces of a third, forming a cross, with fillet welds at the four corners. Load is applied to the pair of arms in line with each other, so it must cross the fillet welds twice to get from one arm to the other. It is a common structural detail and it concentrates the whole load path into welds whose section nobody measured after the fact.
Is the throat worth measuring even though it is hidden?
Yes, before the joint is closed up or on a sectioned sample afterwards. The strength depends on the throat achieved rather than the throat specified, and fillet throats vary substantially with fit-up, gap and technique. Reporting the measured throat alongside the strength is what allows a low result to be attributed to the weld size rather than to the weld metal.
Running ISO 9018 on the Series 7200 and Series 9000
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 | High — a cruciform coupon in structural plate commonly needs 100 kN or more | 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 over the working range | ISO 7500-1 Class 0.5 — a class tighter than the method asks |
| Gripping | Wedge grips sized for the plate thickness, holding the two loaded arms of the joint | Our self-tightening serrated wedge grips, with V-jaws for round specimens, built to the specimen |
| Environment | 23 ± 2 °C standard laboratory atmosphere | 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.