TJ-144
Heavy Duty Hydraulic Grips
For the shear tension coupons: flat serrated faces wide enough for the full coupon, with consistent clamping force across a long current series where the current is meant to be the only variable.
SpecificationsTesting standard
AWS D8.9
Test Methods for Evaluating the Resistance Spot Welding Behavior of Automotive Sheet Steel Materials
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
AWS D8.9, published as AWS D8.9M, is the automotive industry's collected set of laboratory procedures for evaluating how a sheet steel behaves when it is resistance spot welded. Its answers are curves and windows rather than single numbers: a weldability lobe, an electrode life, a hold-time sensitivity, plus shear tension and cross tension strengths. The current edition is AWS D8.9M:2022.
At a glance
- Test type
- Peel & adhesion — a bonded joint is pulled apart
- Published by
- AWS
- Edition
- 2022
- Runs on
- Series 7200 and Series 9000
What the test does
D8.9 is not a single test. It is the automotive industry's collected set of laboratory procedures for finding out how a given sheet steel behaves when it is spot welded, and it contains several tests that are run together to answer that question: weldability lobe determination across a range of welding current, electrode life or endurance testing, hold-time sensitivity, weld hardness, shear tension strength and cross tension strength.
The mechanical parts of it are what reach a universal testing machine. A shear tension specimen is a lap joint containing one weld, pulled along the plane of the sheets. A cross tension specimen is two strips welded in a cross and pulled apart through the thickness. Both are loaded to failure and both are reported with the failure mode.
What it measures, and why it matters
The point of D8.9 is not a single number but a window. Welding current is stepped up while weld time and electrode force are held constant, welds are made at each current, and the resulting strengths and nugget sizes are plotted. The lower bound of the usable range is the current at which the nugget first reaches minimum acceptable size; the upper bound is the current at which expulsion begins. The gap between them is the weldability lobe, and its width is what tells a body engineer whether a steel can be welded reliably on a production line where nothing is perfectly consistent.
Hold-time sensitivity is the other result that matters commercially. Some advanced high-strength steels lose cross tension strength badly when the electrodes are held on the weld after the current stops, because the nugget quenches into hard martensite through the copper. A steel that passes on shear strength alone can fail this, and it is the sort of finding that changes which grade goes into a part.
Coupons, and how many of them
The mechanical coupons are conventional. What is not conventional is the quantity: a lobe study is a population, not a set of five.
- Shear tension coupon
- A lap joint containing one spot weld
- Cross tension coupon
- Two strips welded at right angles
- Material
- Automotive sheet steel, coated or uncoated
- Coupon dimensions
- Specified in the document, sized so failure occurs at the weld
- Coating
- Left on — it is part of what determines nugget growthPractice
- Population for a lobe study
- Several welds at each current level across the whole usable rangePracticePlus the coupons consumed by nugget sizing. Electrode endurance testing runs to several hundred welds on its own.
- Weld the coupons on the schedule being assessed
- DakThe document evaluates a material and a schedule together. Coupons welded on a convenient setting rather than the one under study answer a question nobody asked.
What is varied, and what is held
- Variable
- Welding current, stepped across the range
- Held constant
- Weld time and electrode forceA lobe drawn at one electrode force cannot be compared with a lobe drawn at another. Both are correct and they describe different processes.
- Hold time
- Varied deliberately in the hold-time sensitivity test
- Mechanical test rate
- As specified in the document; not publicly quotable
- Reported
- Strength and failure mode at each condition, plus nugget size
The window, not the number
Weldability lobe—
Nugget size and strength plotted against welding current
- lower bound
- the current at which the nugget first reaches minimum acceptable size
- upper bound
- the current at which expulsion begins
The width of the gap is the result. It says whether the steel can be welded reliably on a line where nothing is perfectly consistent.
Hold-time sensitivity—
Cross tension strength compared across hold times
Some advanced high-strength steels lose cross tension strength badly at long hold times, because the nugget quenches into hard martensite through the copper electrodes. A grade that passes on shear strength alone can fail this.
Electrode endurance—
Welds made before the nugget falls below minimum size
A count, and a commercially significant one: it sets electrode dressing intervals on the line.
How the mechanical work runs
- 01Fix weld time and electrode force for the series.
- 02Step the welding current across the range from undersized nugget to expulsion.
- 03Weld several coupons at each current level.
- 04Size the nuggets by peel or by section to find the lower bound.
- 05Note the current at which expulsion begins to find the upper bound.
- 06Test shear tension coupons with packing shims in both grips.
- 07Test cross tension coupons in the bolted cross-tension jig.
- 08Record peak force and failure mode for every coupon.
- 09Plot strength and nugget size against current.
- 10Repeat at the hold times required for the sensitivity assessment.
- 11Report the lobe, not a single strength figure.
Quoting one shear tension force as an AWS D8.9 result is the commonest misuse of this document. The document produces a window; a single number taken out of it carries none of the information the study was run to get.
Grips and fixtures for this method
Self-identifying
Load Cells
A cell sized for the joint. Shear tension on automotive sheet fails in the low tens of kilonewtons and cross tension lower still, so a cell chosen for the frame throws away resolution across the whole lobe.
SpecificationsWhat the report has to contain
- Reference to AWS D8.9M and the edition
- Steel grade, coating type and mass, and sheet thickness
- Electrode material, geometry and dressing regime
- Weld time, electrode force and hold time
- Welding current at every level tested
- Nugget size at each level, and how it was measured
- Shear tension and cross tension force at each level
- Failure mode for every coupon
- The plotted lobe with its lower and upper bounds
- Which parts of the document were performed, and which were not
What the machine must be capable of
Shear tension of a spot weld in automotive sheet fails in the low tens of kilonewtons at most; cross tension fails lower still. A 50 to 100 kN frame with force accuracy to ISO 7500-1 Class 1 or ASTM E4 covers the mechanical work, and clean resolution at the bottom of the range matters more than capacity.
Shear tension needs flat grips with serrated faces and packing shims of the sheet thickness in both jaws, so the two sheets are pulled in line rather than being progressively peeled. Cross tension needs a dedicated jig that bolts to the four arms of the cross specimen and applies the load normal to the weld. Data rate has to be high enough to capture a peak that arrives without warning.
The rest of D8.9 — the welder, the current monitor, the electrode force gauge, the metallographic work behind nugget sizing — is welding-shop equipment rather than testing-machine equipment, and a laboratory quoting D8.9 capability should be clear about which parts of the document it actually performs.
What goes wrong in practice
Reporting a single strength figure as though it were a D8.9 result is the commonest error, because the document's answers are curves and windows rather than numbers. Missing packing shims on the shear tension specimen, uneven bolt torque on the cross tension jig, and a logger too slow for the peak are the mechanical faults, and they are the same ones the ISO methods suffer. Comparing a lobe drawn at one electrode force with a lobe drawn at another is a subtler error and a common one.
AWS D8.9 and the ISO spot-weld methods
They overlap in the mechanical tests and differ in what the document is for.
| AWS D8.9 | ISO 14273 / 14272 / 14270 | |
|---|---|---|
| What it is | An evaluation suite for a steel and a schedule | Three single test methods |
| Output | A weldability lobe, an electrode life, a sensitivity | A force and a failure mode |
| Mechanical tests included | Shear tension and cross tension | Shear, cross tension and peel, one per document |
| Beyond the testing machine | Welding, current monitoring, hardness, metallography | None — the weld arrives already made |
| Where it is specified | North American automotive practice | International and European automotive practice |
Coupon geometry and reporting are not identical between the two families. A shear tension force obtained to D8.9 and one obtained to ISO 14273 are close relatives and are not interchangeable numbers.
Questions we are asked about this test
What is AWS D8.9?
AWS D8.9, published as AWS D8.9M, is the American Welding Society's set of test methods for evaluating the resistance spot welding behaviour of automotive sheet steel. It bundles weldability lobe determination, electrode endurance, hold-time sensitivity, weld hardness, shear tension strength and cross tension strength into one document. The current edition is AWS D8.9M:2022, superseding D8.9M:2012, with the series running back through AWS/SAE D8.9M:2002 to a first edition in 1997.
Why is the designation sometimes written D8.9M?
The M denotes that the document is issued in metric units only. Older AWS practice published dual-unit and inch-pound editions alongside metric ones, and the suffix survives to say which this is. D8.9 and D8.9M refer to the same document in ordinary use.
What is a weldability lobe?
It is the range of welding current over which acceptable welds can be made, with weld time and electrode force held constant. The lower bound is the current at which the nugget first reaches minimum acceptable size; the upper bound is the current at which expulsion begins. The width of that window is the practical result, because a production line varies and a narrow lobe means welds will drift out of it. Widening the lobe is what most spot-welding development work is trying to achieve.
What does hold-time sensitivity find?
Steels whose welds embrittle when the electrodes stay clamped after the current stops. The nugget quenches rapidly through the copper, and in some advanced high-strength grades that produces a hard martensitic nugget with poor cross tension strength. The shear strength can look entirely healthy while this is happening, which is why the sensitivity test is run in cross tension and why it sometimes changes which grade goes into a part.
How much of D8.9 does a testing laboratory actually perform?
Usually the mechanical part: shear tension and cross tension to failure, with peak force and failure mode recorded. The welding itself, the current monitoring, the electrode force measurement, the hardness traverses and the metallographic nugget sizing are welding-shop and laboratory work of a different kind. A supplier quoting D8.9 capability should say which clauses it performs, because the document is much wider than the testing machine.
Can an ISO 14273 result be reported as a D8.9 result?
No. The two shear tension procedures are close relatives, but the coupon geometry and the reporting requirements are not identical, and D8.9 expects the strength to sit inside a lobe study rather than to stand alone. Where a customer specification names one document, run that one and say so; substituting the other is a reporting error even when the numbers come out similar.
What machine does the mechanical work need?
A 50 to 100 kN frame with force accuracy to ASTM E4 or ISO 7500-1 Class 1 covers automotive sheet, with resolution at the bottom of the range mattering more than capacity. Shear tension needs flat serrated grips and packing shims of the sheet thickness in both jaws; cross tension needs a bolted jig that loads the weld normal to the sheet. In both cases the data rate must be high enough to catch a peak that arrives without warning.
Running AWS D8.9 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 | Shear tension in the low tens of kN on automotive sheet; cross tension lower still | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | ASTM E4 or ISO 7500-1 Class 1 | Verified to ASTM E4, and to ISO 7500-1 Class 0.5 |
| Gripping | Flat serrated grips with packing shims for shear tension; a bolted cross-tension jig for cross tension | Our self-tightening serrated wedge grips, with V-jaws for round specimens or a fixture built for this method, built to the specimen |
| Environment | Ambient laboratory conditions for the mechanical tests | 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.