Scope:

The Free Falling dart method ASTM D1709 is the conventional method for assessing the stiffness or strength of plastic sheets. A single dart model and a single drop-test height are used while the weight of the dart is varied during the test.

Test Procedure:

For the ASTM D1709 test, there are two methods and the choice of method A or method B depends upon a sample’s impact strength. In method A, dart size and the drop-test height are determined as per the method chosen. A number of samples are then impacted to fix an appropriate starting point for the weight of the dart. The test sample is mounted securely in an aerial ring at the pedestal of the drop tower. The mounting bracket is fine-tuned to a certain drop height before inserting the dart into the bracket. As the dart is released, it impacts the center of the test sample. The drop weight is measured precisely. Finally, the test record (pass/fail) is registered.

Bruceton Staircase is a method that gives the most precise way of analyzing this data. As many as 20 specimens are used to bracket the pass/fail energy grade. Gradually the distance is increased, and as the weight drops, the failure point is determined. Specimens, up to 20, are generally used for known estimated mean-failure height. In case a test sample has passed, drop height will be moved ahead by one unit. In case a sample fails, drop height goes back one unit. Mean failure height that is the point at which 50 percent of the test samples undergoing impact fail, is then calculated using the results obtained from 20 impacts. 

Test method A details a dart with a 38 mm (1.5 inches) diameter. The drop height is from 0.66 m (26 inches). Test method B details a dart with a 51 mm (2.0 inches) diameter. The Drop height is from 1.5 m (60 inches).

Specimen size:

Plastic sheet samples of dimension 230 mm × 230 mm (9 inches × 9 inches) are cut out for use. Thirty samples minimum are required for the test method.

Data:

Impact failure weight (g) 

Conclusion:

ASTM D1709 is a standard test method for measuring impact resistance of plastic film by the free falling dart.