Self-tighteningTJ-15
Universal Parallel Wedge Grips
Parallel wedge grips with flat faces hold a lap-shear coupon squarely; the offset built into the specimen means the grips must not add any of their own.
SpecificationsTesting standard
ISO 4587
Adhesives — Determination of tensile lap-shear strength of rigid-to-rigid bonded assemblies
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ISO 4587 pulls a single-lap bonded joint between two rigid adherends until it fails and reports the failure load divided by the bonded area. The standard states that the procedure does not provide design information: the joint is not in pure shear, so the number compares adhesives rather than sizing a bond.
At a glance
- Test type
- Shear
- Published by
- ISO
- Edition
- ISO 4587:2003
- Material
- Adhesives, tapes & bonded joints
- Runs on
- Series 7200 and Series 9000
What the test does
Two rigid adherends, prepared to a specified surface treatment, are bonded over a defined overlap at a controlled bond-line thickness, cured and conditioned. The assembly is then gripped at each end and pulled in line at a constant rate until the joint fails. The failure load is divided by the measured bonded area to give a lap-shear strength in megapascals, and the fracture surfaces are examined so the failure can be classified as cohesive through the adhesive, adhesive at the interface, or a stated mixture of the two.
What it measures, and why it matters
A comparison, and the standard is unusually direct about it: the procedure does not provide design information. The reason is geometric. The two adherends carry load along lines offset by the thickness of the joint, so the assembly bends as it is pulled and the bond experiences peel as well as shear, concentrated at the ends of the overlap while the middle carries comparatively little. The reported strength is a nominal average over an area whose stress is nothing like uniform. What it does well is rank adhesives, surface treatments and process changes against one another under identical conditions.
The overlap
Two rigid adherends bonded over a defined overlap, then pulled in line. The offset between them is what makes the stress non-uniform.
- Configuration
- Single lap, two rigid adherends
- Loading
- In tension, along the adherendsBecause the load paths are offset, the joint bends as well as shears. That is inherent, not a defect.
- Stress distribution
- Concentrated at the ends of the overlapThe middle of a lap joint carries much less than the edges, so strength does not scale with overlap area.
- Reported
- Failure load divided by the bonded areaA nominal average, and everyone using it should know it is nominal.
- Adherend preparation
- As specified, and identical across the set
- Record the failure mode as a percentage
- Cohesive, adhesive or mixedDakA high strength that failed adhesively at the interface is a surface preparation result, not an adhesive result.
The standard says outright that this test does not provide design information. It is a comparison between adhesives, surface treatments and processes under identical conditions.
Test speed
- Rate
- The constant rate the standard specifies
- Reported
- Lap-shear strength, in MPa
- Alignment
- Shimmed or self-aligning so the load line passes through the bondWithout shims the specimen straightens as it loads and adds peel at the overlap ends.
- Photograph the failure surfaces
- Both halvesDak
Calculations
Lap-shear strengthτ
τ = F / (l × b)
- F
- failure load, N
- l
- overlap length, mm
- b
- overlap width, mm
A nominal average over the bonded area. The real stress peaks at the ends of the overlap and is much lower in the middle, which is why doubling the overlap does not double the strength.
Failure mode—
Percentage cohesive, adhesive and mixed failure across the bond area
Reported alongside the strength. Two adhesives with identical strengths and different failure modes are telling you different things.
How the test runs
- 01Prepare adherends to the specified surface treatment, identically across the set.
- 02Bond to the specified overlap length and bond-line thickness.
- 03Cure under the specified conditions and record them.
- 04Condition the assemblies before testing.
- 05Measure the actual overlap length and width on each specimen.
- 06Fit parallel wedge grips and shim the specimen so the load line passes through the bond.
- 07Load at the specified constant rate to failure.
- 08Record the failure load.
- 09Calculate the strength on the measured bonded area.
- 10Assess and record the failure mode as percentages of cohesive, adhesive and mixed.
- 11Photograph both failure surfaces.
Grips and fixtures for this method
Standard 25 mm
Pneumatic Vice Action Grip
For thin or coated adherends where a wedge would mark the surface.
SpecificationsWhat the report has to contain
- Reference to ISO 4587 and the edition
- Adhesive identification and batch
- Adherend material, thickness and surface treatment
- Overlap length and width as measured, and bond-line thickness
- Cure schedule and conditioning
- Rate of traverse
- Failure load and calculated lap-shear strength for each specimen
- Failure mode as percentages
- Alignment or shimming arrangement used
- Photographs of the failure surfaces
What the machine must be capable of
Modest capacity — a structural adhesive on a standard overlap commonly fails between one and twenty kilonewtons — with parallel wedge grips and, more importantly, a way of bringing the line of pull through the bond. Shims or self-aligning grips are not an optional refinement: without them the offset specimen straightens as it loads, adding rotation and peel at the overlap ends on top of the eccentricity the geometry already has, and the joint fails early. Good alignment is the difference between measuring the adhesive and measuring the fixture.
What goes wrong in practice
Reporting a strength without a failure mode, which discards the information that says whether to change the adhesive or the surface treatment. Comparing coupons made with different overlap lengths, where the longer one reads weaker because the added area is in the lightly-stressed middle. Uncontrolled bond-line thickness. Testing without shims. And — the most consequential in engineering terms — treating the megapascal figure as an allowable shear stress for a real joint, which is precisely the use the standard rules out. Where a joint genuinely has to be sized, the route is a stress analysis of the actual geometry with the adhesive's own properties as inputs, using lap-shear results to choose the adhesive rather than to set the allowable.
ISO 4587 or ASTM D1002
| ISO 4587 | ASTM D1002 | |
|---|---|---|
| Family | ISO | ASTM |
| Configuration | Single lap, rigid adherends | Single lap, metal adherends |
| Design information | Explicitly not provided | Explicitly a comparison |
| Failure mode | Recorded | Recorded |
Two routes to the same comparison, with different specimen dimensions, so the strengths are not interchangeable. Cite the designation your specification names and keep one method within a data set.
Questions we are asked about this test
What is ISO 4587?
It is the ISO method for the tensile lap-shear strength of rigid-to-rigid bonded assemblies. Two rigid adherends are bonded over a defined overlap and pulled apart in line, and the failure load is divided by the bonded area to give a strength in megapascals. The current edition, the third, is ISO 4587:2003.
Why does the standard say it does not provide design information?
Because the joint is not in pure shear. The two adherends carry load along offset lines, so the assembly bends as it is pulled and the bond sees peel as well as shear, concentrated at the ends of the overlap. The middle of the bond carries comparatively little. The figure that comes out is a nominal average over an area whose stress is far from uniform — useful for comparing adhesives under identical conditions, and not a stress a designer can size a real joint against.
Why doesn't a longer overlap give proportionally more strength?
Because the extra length is added in the middle, where the stress is lowest. Load transfer in a lap joint concentrates at the two ends of the bond, and lengthening the overlap mostly adds lightly-stressed area. The failure load rises, but far less than in proportion, so the calculated strength falls — which looks like a worse adhesive and is only a longer specimen.
Why does the failure mode matter as much as the strength?
Because it says where the weakness is. A cohesive failure, through the adhesive layer itself, means the adhesive was the limiting element and the surface preparation did its job. An adhesive failure at the interface means the bond to the substrate gave way, which is a surface treatment or contamination problem and will not be fixed by a stronger adhesive. Two specimens can record the same strength and require opposite responses.
Why does the specimen need shimming?
Because the two adherends are offset by the thickness of the joint, so under load the specimen tries to straighten. That rotation adds a peel component at the ends of the overlap, on top of the peel already inherent in the geometry, and the joint fails earlier. Shims or self-aligning grips bring the line of pull through the bond so that only the geometry's own eccentricity is present, which is the condition the method assumes.
Does the bond-line thickness need controlling?
Yes, and it should be reported. A thicker bond line changes both the stiffness of the joint and the volume of adhesive available to deform, so it shifts the measured strength independently of the adhesive itself. Comparing two adhesives at different bond-line thicknesses confounds the comparison the test exists to make, which is why the thickness is a controlled parameter rather than whatever the assembly produced.
Can ISO 4587 results be compared with ASTM D1002?
Not directly. Both run a single-lap coupon and both describe themselves as comparisons rather than design data, but specimen dimensions differ, and lap-shear strength depends on the overlap geometry. Keep one method within a data set and cite the designation the specification names.
Running ISO 4587 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 | Low to moderate — a structural adhesive on a standard overlap commonly fails between 1 and 20 kN | 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 | Parallel wedge grips, with shims or self-aligning grips to bring the two adherends into line | 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.