Ball burst is a bursting test widely specified for knitted garments, particularly under ASTM methods. A ring clamp holds a circular area of fabric, and a polished steel ball is driven through it until it ruptures. The result is a force, not a pressure.
It looks simple. But the same fabric can produce different ball burst figures in two laboratories that both believe they ran "the ball burst test" — because there are several of them.
One ball, several standards
| Standard | Material | Machine principle |
|---|---|---|
| ASTM D3787 | Woven and knitted textiles | Constant rate of traverse (CRT) |
| ASTM D6797 | Woven and knitted textiles | Constant rate of extension (CRE) |
| ISO 9073-5 | Nonwovens | Mechanical penetration by a ball |
| ISO 3303-1 | Rubber- or plastics-coated fabrics | Steel ball method |
The first two rows are the source of most confusion. ASTM D6797 itself notes that CRT and CRE machines have been shown to give different results. A buyer who specifies D3787 and a lab that runs D6797 on a modern universal tester are not doing the same test, even with the same ball and the same ring.
Report the method number, not "ball burst".
The geometry is fixed — keep it that way
ASTM D3787 uses a polished steel ball 25.4 mm (1 in) in diameter and a ring clamp with a 44.45 mm (1.75 in) opening. These dimensions define how much fabric is loaded and how sharply it is curved around the ball. Any change alters the result.
Common problems at the bench:
- Damaged ball. A ball that has been dropped, scratched or corroded no longer slides cleanly over the fabric. Friction rises and the result changes. Inspect the ball under good light and replace it if the surface is marked.
- Wrong ring. Attachments for other standards may sit in the same drawer. A ring of a different diameter fits mechanically but changes the test.
- Ball off-centre. The ball must travel through the centre of the ring. An offset ball loads one side of the specimen first and bursts it early.
Clamping decides more than the ball
The fabric must be held so it cannot draw into the ring as the ball advances. If it slips, part of the ball's travel is spent pulling fabric in rather than stretching it, and the measured force no longer represents the fabric.
- Cut specimens large enough to extend well beyond the clamp on all sides.
- Use the clamping force the instrument is designed for; on screw clamps, train operators to tighten consistently.
- Inspect each burst specimen. A rupture that starts at the edge of the ring, or a ring of slipped fabric, marks an invalid test.
Knits with high stretch are the most prone to slippage — which is unfortunate, because they are exactly the fabrics ball burst is most often used for.
Speed and machine type
D3787 specifies a constant rate of traverse of the ball (305 mm/min, 12 in/min). On a CRT machine the ball moves at constant speed regardless of the fabric's resistance. On a CRE tensile tester fitted with a ball burst attachment, the extension rate is held constant instead, and the load–time history differs.
If your lab runs ball burst on a universal testing machine, you are almost certainly running a CRE test. That is fine — report it as such. What is not fine is labelling a CRE result as ASTM D3787.
Ball burst or diaphragm burst?
Diaphragm bursting (ISO 13938-1/-2, ASTM D3786) applies fluid pressure over the whole test area. Ball burst applies a concentrated mechanical load at the centre. They answer slightly different questions, and there is no conversion between a ball burst force and a diaphragm pressure.
Ball burst tends to be preferred for very extensible knits and elastic nonwovens. ISO 9073-5 states that it is designed primarily for nonwovens with some degree of elasticity, for which a regular burst test does not apply. A diaphragm can reach the limit of its own stretch before a highly extensible fabric fails; a ball keeps pushing.
Conditioning and wet tests
Ball burst force is sensitive to moisture, particularly for cellulosic and polyamide knits. Condition specimens to ISO 139 and test promptly after removal from the conditioning atmosphere. If a wet result is required, follow the wetting procedure of the method and label the result as wet.
A short set-up routine
- Confirm the method: ASTM D3787, ASTM D6797, ISO 9073-5 or ISO 3303-1.
- Check ball diameter, ring opening and ball surface.
- Confirm the ball travels centrally through the ring.
- Set the speed from the standard and record it.
- Zero the force reading with the ball clear of the specimen.
- Inspect every burst for clamp-edge failure or slippage before accepting the result.
A lab that follows these six steps can defend its ball burst figures against any buyer audit. A lab that skips step 1 will eventually find itself comparing CRT and CRE numbers without realising it.
Our ball bursting tester is supplied with a 25.4 mm polished steel ball, a 44.45 mm test head and USB data output. It is manufactured in our own workshop in Istanbul.