Testing standard
Standard Test Methods for Rubber Property—Adhesion to Flexible Substrate
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ASTM D413 measures how firmly vulcanised rubber is bonded to a flexible substrate — usually a textile ply. Two plies are separated at a controlled rate and the peel force per unit width is recorded. It is the property that decides whether a hose, a belt or a coated fabric holds together in service, because those articles fail between plies far more often than they fail in tension.
Two bonded plies — vulcanised rubber against a flexible substrate, most often a textile — are separated at a controlled rate while the force is recorded. A short length is freed by hand to start the peel, then one ply is clamped in each grip and the crosshead separates them at about 50 mm/min. The force is averaged over a steady length, the run-in transient discarded, and divided by the measured bonded width. Where the specification calls for it, the strip arrangement holds one ply against a support instead, which is closer to how a ply lifts inside a hose wall.
The result is ply adhesion in force per unit width, together with the mode of failure. It matters because laminated rubber articles almost never fail in tension. A hydraulic hose, a conveyor belt, a timing belt or a coated fabric is a laminate, and what actually happens in service is that plies separate — from repeated flexing, from heat, or from a defect in the cement layer laid down during manufacture. Once a ply lifts, the interaction that gave the construction its strength is gone, and the tensile figure on the datasheet is no longer available to it. Ply adhesion is the property that predicts that, and nothing else does.
A flexible-to-flexible bond behaves differently from rubber on metal: both sides can stretch, so how the free ends are held changes what the peel front feels.
Report where the failure ran. Rubber tearing within itself means the bond beat the compound; fabric pulling apart means the textile did; a clean interface means the bond was the weak link. Only the last is a bonding problem.
Adhesion = average peel force / bonded width
Reported as force per unit width, in N/mm or kN/m. Never as a stress — there is no meaningful area at a peel front.
Pneumatic vice action grips hold a constant clamping force on two plies of quite different stiffness — a fabric ply and a rubber ply behave differently under a screw grip that keeps bedding in as the rubber relaxes.
SpecificationsLow forces measured accurately: peel forces here commonly run from tens of newtons to a few hundred over a 25 mm width, so resolution at the bottom of the load cell's range matters far more than capacity. The crosshead must hold 50 mm/min steadily and have enough travel to peel a useful length after the run-in is discarded. The grips carry the awkward requirement, because they hold two materials of very different stiffness at once — a fabric ply and a rubber ply — and a screw grip keeps bedding in as the rubber relaxes beneath it. A constant-force pneumatic grip holds both without that drift.
The peel angle drifting is the characteristic problem, and it is specific to flexible-to-flexible bonds: both sides stretch under load, so an unconstrained peel opens up as the test proceeds and the force falls for a geometric reason that has nothing to do with the bond. Reporting only the average is the second: a trace that declines steadily along the specimen is telling you the cement was applied unevenly, which is a process finding an average discards. Omitting the failure mode is the third, since rubber tear, fabric tear and a clean interface point at three completely different causes. And using the cutter setting rather than the measured width puts a quiet systematic error into every figure.
| ASTM D413 | ASTM D429 | |
|---|---|---|
| Substrate | Flexible — fabric, cord, another rubber ply | Rigid — almost always metal |
| What can stretch | Both sides | Only the rubber |
| Typical article | Hose, belting, coated fabric | Mount, bush, roller |
| Result | Force per unit width | Force, or force per unit width by method |
The two are not alternatives. A flexible-to-flexible peel and a rubber-to-metal peel are different mechanics, and a value from one says nothing about the other.
It is the ASTM test method for the adhesion of vulcanised rubber to a flexible substrate, usually a textile ply. Two plies are separated at a controlled rate and the peel force per unit width is recorded, together with where the failure ran.
Because those articles almost never fail in tension. A hose or a conveyor belt is a laminate, and what actually happens in service is that the plies separate — from flexing, from heat, from a manufacturing defect in the cement layer. Once a ply lifts, the construction has lost the interaction that gave it strength, and the tensile figure that appears on the datasheet is no longer available.
The substrate, and therefore the mechanics. D429 bonds rubber to a rigid substrate, where only the rubber can stretch. D413 bonds it to a flexible one, where both sides deform and the peel geometry changes as the test proceeds. A value from one says nothing about the other.
Because both plies are flexible. On rubber-to-metal the substrate holds its shape and the angle stays where it was set; here, both sides stretch under load, so an unconstrained peel opens up as the test proceeds and the force falls for a purely geometric reason. Watching the angle through the run, and using the arrangement the specification names, keeps it comparable.
Usually cement applied unevenly across the ply. A peel force that declines steadily along the specimen is telling you the bond varies down the length, which is a process finding rather than a material one. Averaging it into a single number hides exactly the information the trace is offering.
Rubber tearing within itself. That means the bond is stronger than the compound and there is nothing left to improve at the interface. Fabric pulling apart means the textile is the limit. A clean separation at the interface is the only outcome that points at the bonding process, and it is the only one worth chasing.
For the adhesion question, yes — it is the standard way of asking whether a coating will stay attached to its substrate. The wider set of properties for a coated fabric, including breaking strength and tearing strength, sits in ASTM D751, and the two are usually specified together.
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 — commonly 20 N to 500 N over a 25 mm bonded width | 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 | Verified to ASTM E4, and to ISO 7500-1 Class 0.5 |
| Gripping | Tensile grips holding the two plies; a machine-driven roller where the specification requires the 90° arrangement | Our peel and adhesion fixtures, 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.
