Falling dart impact is a traditional method for evaluating the impact strength or toughness of a plastic film. This test uses a single dart configuration and a single drop height, while varying the weight of the dart. Test results can be used either as a quality control evaluation or for end use comparisons.
Depending upon the expected impact strength of the test sample, either Method A or Method B is chosen. The method defines the dart size and the drop height for the dart. A number of test samples are then impacted to determine an appropriate starting point for the weight of the dart.
The test specimen is clamped securely in a pneumatic ring at the base of the drop tower. The mounting bracket is adjusted to the appropriate drop height, and the dart is inserted into the bracket. The dart is released to drop onto the center of the test specimen. The drop weight and the test result (pass / fail) are recorded.
The method to analyze this test data is called the "Bruceton Staircase" method. A series of 20 to 25 impacts are conducted. If a test specimen passes, the drop weight is increased by one unit. If a test specimen fails, the drop weight is decreased by one unit. The results from these impacts are used to calculate the Impact Failure Weight - the point at which 50% of the test specimens will fail under the impact.
Test method A specifies a dart with a 38 mm (1.5") diameter dropped from 0.66 m (26")
Test method B specifies a dart with a 51 mm (2") diameter dropped from 1.5 m (60")
Film samples that can be cut to 230 mm x 230 mm (9" x 9") specimens
A minimum of 30 specimens are required for the test
Impact failure weight (grams)
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Free-falling dart impact tester