Ultimate Guide to ASTM D1709 & ISO 7765-1

What Is the Falling Dart Impact Test?

The free-falling dart impact test (ASTM D1709 / ISO 7765-1 / GB/T 9639.1) measures the energy required to cause a plastic film or sheet (typically less than 1 mm thick) to fail under a controlled impact of a falling dart. It is widely used as a benchmark for film toughness in food packaging, medical packaging, and industrial applications.

In practice, a hemispherical dart of known geometry is dropped from a fixed height onto a clamped film sample. By varying the mass of the dart and recording whether the sample passes or fails, the test quantifies the impact resistance in a way that correlates with real-world handling and logistics events.

Method A vs. Method B: Which Do You Need?

ASTM D1709 and ISO 7765-1 define two main methods, A and B, which differ in drop height and dart size.

1. Method A:

- Drop Height: 0.66 m (26 inches).

- Dart Head: 38.10 mm (≈38 mm) hemispherical dart, usually phenolic or aluminum.

- Typical Applications: Thin to medium-thickness films for consumer packaging, such as snack bags, laminates for pouches, and general flexible packaging.

2. Method B:

- Drop Height: 1.50 m (≈60 inches).

- Dart Head: 50.80 mm (≈50 mm) hemispherical dart, often stainless steel.

- Typical Applications: Films with higher impact strength within the standard thickness range, including heavy-duty bags, pallet wraps, and more robust industrial films.

The choice between Method A and B generally depends on the expected impact resistance of the film: Method A for lower to medium toughness, Method B for higher toughness or thicker structures that still fall within the <1 mm scope of ISO 7765-1 and GB/T 9639.1.

Understanding the Staircase Method

The staircase (up-and-down) method is the standard statistical technique in ASTM D1709 and ISO 7765-1 for determining the impact failure mass, often referred to as M50—the dart mass at which 50% of specimens fail.

The basic logic:

- Start with an estimated dart mass based on preliminary trials.

- If the sample fails, reduce the dart mass by a fixed increment for the next specimen.

- If the sample does not fail, increase the dart mass by the same increment.

- Continue this up-and-down sequence until sufficient data points (usually at least 20) are collected.

The MLB-01 automates this procedure:

- The touchscreen interface guides the operator through each drop and records pass/fail results.

- The integrated microcomputer performs the staircase calculation and outputs the M50 value along with supporting statistics.

- This automation reduces calculation errors and ensures that every operator applies the same algorithm consistently.

Why Pneumatic Clamping and Clean Release Matter

Test accuracy in dart impact is strongly influenced by how the sample is held and how the dart is released.

- Pneumatic Clamping: Manual clamps are prone to variation. If the clamp is too loose, the film slips and absorbs less energy; if too tight, the film may be pre-stressed or damaged. The MLB-01 uses a pneumatic ring clamp with a defined pressure range and standard-compliant rubber gasket, minimizing operator influence and slippage.

- 3-Jaw Pneumatic Release: Electromagnetic releases can introduce residual magnetism and inconsistent starting conditions—especially for very light darts. KHT’s 3-jaw pneumatic gripper holds and releases the dart mechanically, ensuring a vertical, interference-free drop for each test.

For labs seeking reliable, audit-ready data, these hardware details are just as important as following the correct standard method on paper.