Testing standard
ASTM D6797
Standard Test Method for Bursting Strength of Fabrics Constant-Rate-of-Extension (CRE) Ball Burst Test
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ASTM D6797 measures the bursting strength of textiles with a constant-rate-of-extension machine. A 25.4 mm polished steel ball rides on the crosshead and advances into a disc of fabric held by a ring clamp until it opens. The height of the force trace at that instant is the whole result — nothing else is reported.
At a glance
- Test type
- Puncture & burst
- Published by
- ASTM
- Edition
- D6797-24
- Runs on
- Series 7200 and Series 9000
What the test does
The moving member does the work here. A 25.4 mm polished steel ball rides on the crosshead and advances, at a rate held constant throughout, into a disc of fabric under 45 mm across that the ring clamp holds still and grips right round its rim. Forced to follow the crown of a sphere, the cloth thins and tightens until it opens. The height of the force trace at that instant is the whole result; nothing else is reported.
What it measures, and why it matters
The reported quantity is bursting force: the peak the frame reaches before the ball goes through.
Read plainly, that is a fabric's tolerance for a concentrated out-of-plane load — the elbow inside a knitted sleeve, the blunt corner met by a nonwoven liner, the minimum burst written into a protective-textile specification. The figure is biaxial by construction, and that is both its use and its limit: because no yarn direction can be loaded on its own, a burst result cannot be decomposed. It says the structure as a whole gave way at that force in that geometry, not which system went first. It is an acceptance and ranking number, not a design allowable, and does not convert to a pressure rating.
Specimen and clamp
- Exposed disc
- Under 45 mm across
- Clamp
- Ring, gripping right round the rimThe cloth is held still; the ball comes to it.
- Ball
- 25.4 mm polished steel, on the crosshead
- Moving member
- The BALL advancesThis is the distinction from ASTM D3787, where the clamp traverses.
- Reported
- Peak force alone
- Check for rim slippage
- On every specimenDakFabric drawing in at the clamp inflates the peak, and the trace looks entirely normal.
Test speed
- Machine type
- Constant rate of extensionCRE — the distinction the method name carries.
- Rate
- Held constant throughout
Calculations
F = peak force, in newtons
A force. As with the CRT method, this does not convert to the pressure a hydraulic diaphragm test reports.
How the test runs
- 01Condition the fabric in the textile standard atmosphere.
- 02Cut specimens large enough for the ring to grip fully.
- 03Clamp so the exposed disc is taut but unstretched.
- 04Fit the polished ball to the crosshead.
- 05Advance at the constant rate into the centre of the disc.
- 06Continue until the fabric opens.
- 07Record peak force.
- 08Inspect the rim for slippage and discard the specimen if it drew in.
What the report has to contain
- Reference to ASTM D6797
- Fabric identification, construction and finish
- Ring and ball dimensions
- Conditioning atmosphere
- Rate of extension
- Bursting strength in newtons
- Number of specimens, mean and standard deviation
- Any specimen discarded for clamp slippage
What the machine must be capable of
A constant-rate-of-extension frame is required, with the ball on the moving member and the ring clamp fixed. The distinction is not pedantry: results are stated not to be interchangeable with those from the constant-rate-of-traverse machine of the neighbouring method. Crosshead speed is 305 ± 13 mm/min (12 ± 0.5 in./min); textiles respond to rate, so that is a controlled variable, not an operator preference.
Nowhere does the method name a capacity, so sizing rests on the precision work: the averages published with the superseded edition sit near 766 N and 584 N on two woven fabrics. A low-single-digit-kN frame has ample headroom above that. Choosing the cell is the harder decision, since the reading that matters arrives at the very top of the trace, where resolution is set by the range picked before the run.
An accuracy class cannot be stated with confidence. The 2015 edition invoked no machine specification and no accuracy class at all, unlike its constant-rate-of-traverse counterpart, which cites one directly; whether the 2024 revision added one could not be confirmed, so read the current text rather than assume the counterpart's requirement carries across.
The fixture is fully specified where the frame is not: ring bore 44.450 ± 0.025 mm, ball 25.400 ± 0.005 mm, polished. Those tolerances are what make one laboratory's burst comparable with another's; alter either and the cloth follows a different curvature through a different opening. The method uses no extensometer, and the conditioned atmosphere is itself a requirement.
What goes wrong in practice
Mixing the two ball-burst methods is the commonest error, and it happens in the reporting rather than in the laboratory. A figure quoted as ball burst with no machine class named is unusable, because the two classes return different numbers on the same fabric and both documents say so.
Clamping is next. Too little, and slick or coated fabrics creep inward as the ball advances, giving a low peak on a long, soft curve; too much, and heavy fabrics are crushed at the ring, so the tear starts at the clamp line and the force belongs to the fixture. A specimen burst around the clamp rather than over the ball's crown should be repeated, not averaged in.
Concentricity is easily lost when the fixture is swapped between jobs. An off-centre ball loads one arc of the ring first, and scatter widens before anyone suspects alignment.
The burst family
| ASTM D6797 CRE | ASTM D3787 CRT | ISO 13938-1 hydraulic | |
|---|---|---|---|
| Moving member | The ball | The clamp | A fluid-driven diaphragm |
| Machine | Constant rate of extension | Constant rate of traverse | Pressure-controlled |
| Result | Force, N | Force, N | Pressure, kPa |
| Interchangeable | No | No | No |
D6797 and D3787 differ only in which member moves, and that is enough to change the result. Most modern testing machines are constant-rate-of-extension, which makes D6797 the more commonly available of the two — but availability is not equivalence, and the specification decides.
Questions we are asked about this test
What is ASTM D6797?
It is the ASTM constant-rate-of-extension ball burst test for textiles. A 25.4 mm polished steel ball on the crosshead advances into a disc of fabric held by a ring clamp until the fabric opens, and the peak force at that instant is the whole result.
What is the difference between D6797 and D3787?
Which member moves and therefore which machine type. In D6797 the ball advances on a constant-rate-of-extension crosshead; in D3787 the ring clamp traverses onto a fixed ball on a constant-rate-of-traverse machine. Since most modern frames are CRE, D6797 is the more widely available — but the two are not interchangeable and the specification decides.
Why is only peak force reported?
Because that is the question the test asks: how much force does it take to push a ball through this fabric. Displacement at rupture can be captured but adds little, since the deformation is a complex biaxial draw rather than a strain against a gauge length. The method is deliberately a single number.
When is a burst test better than a tensile test?
For knitted, nonwoven and other fabrics with no clear warp and weft structure, where a directional tensile result would be arbitrary. The ball stretches the fabric in every in-plane direction at once, which is much closer to how such a fabric is loaded in use — a knee pushing through a knit, or a nonwoven under a point load.
Why did my burst strength come out high?
Almost always slippage at the clamp rim. If the fabric draws in rather than stretching, more material deforms than the method intends and the peak force rises — while the force trace looks entirely normal. Inspecting the rim on every specimen is the only reliable check.
Why choose the CRE ball burst over the hydraulic method?
Practicality, mostly. A constant-rate-of-extension machine is already in most textile laboratories, and D6797 puts the ball on the crosshead of that machine, so no separate hydraulic burst tester is needed. The trade-off is that a ball loads the fabric over a small contact area while a hydraulic diaphragm loads the whole dome, so the two are not interchangeable and the method must be named.
Does fabric thickness affect the result?
Yes, and it is not normalised out. The reported quantity is the peak force to burst the clamped area, with no division by thickness or mass, so a heavier fabric of the same construction will read higher. That makes the figure valid for comparing like with like — the same construction across batches — and misleading for comparing fabrics of different weights unless that difference is exactly what is being examined.
Running ASTM D6797 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 | No force capacity is prescribed. The method's own precision tables average about 172 lbf and 131 lbf on two woven fabrics — roughly 766 N and 584 N — and fixture suppliers size ball-burst work for fabrics failing below about 2.2 kN, so a frame of a few kN with a matched load cell covers most fabrics and garments. | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | unknown | ISO 7500-1 Class 0.5 — the method sets no class of its own |
| Gripping | Ball-burst attachment: ring clamp with a polished steel ball carried on the CRE crosshead | Our compression anvils, built to the specimen |
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.