Dart Impact Testing of Plastic Films: ASTM D 1709 Staircase Method Explained

A film's tensile numbers can look excellent while the film still punctures the first time a sharp corner lands on it. Dart impact — free-falling dart method per ASTM D 1709 — measures resistance to that sudden, localised puncture, and it is the specification test for carrier bags, liners, agricultural films and heavy-duty sacks.

The test runs on a Dart Impact Tester: a hemispherical-headed dart is dropped from a fixed height onto a clamped film, and weight is varied until the failure point is bracketed.

The Staircase (Bruceton) Method

The film is clamped over an annular ring, and a dart is released electromagnetically from 0.66 m (Method A, 38 mm dart) or 1.5 m (Method B, 51 mm dart). If the film fails, the next drop uses a lighter dart; if it survives, a heavier one. After a series of 20+ drops the data converges on the weight at which 50 % of specimens fail — reported as the dart impact strength, F50, in grams.

Method A suits most packaging films; Method B, with its higher drop and larger head, is for tougher films whose F50 would exceed Method A's practical weight range.

Getting Trustworthy Dart Data

• Clamping — pneumatic or toggle clamps must grip uniformly; slippage absorbs energy and inflates results.
• Specimen condition — test at standard 23 °C/50 % RH; cold films are dramatically more brittle.
• Statistics — F50 is a statistical result; a single pass/fail drop tells you almost nothing.
• Thickness — always report film gauge with the result, since dart strength scales with thickness.

Dart Impact in the Film QC Suite

Dart impact complements tensile testing (slow-speed strength), COF (handling behaviour) and peel/seal testing (closure integrity). Together they form the core of any film testing laboratory.

Frequently Asked Questions