Gardner Impact Test

Falling dart impact, also known as Gardner impact, is a traditional method for evaluating the impact strength or
toughness of a plastic material. The test is often used to specify appropriate materials for applications involving impact
or to evaluate the effect of secondary finishing operations or other environmental factors on plastic impact properties.

The test sample rests on a base plate over an opening of specified diameter. An “impactor” sits on top of the test
sample with a nose of specified radius in contact with the center of the test sample. A weight is raised inside a guide
tube to a predetermined height, then released to drop onto the top of the impactor, forcing the nose through the test
sample. The drop height, drop weight, and the test result (pass / fail) are recorded.

The most common method to analyze this data is called the “Bruceton Staircase” method. A number of samples are
used to bracket the pass/fail energy level. Then a series of 20 impacts are conducted. If a test sample passes, the
drop height is increased by one unit. If a test sample fails, the drop height is decreased by one unit. The results from
the 20 impacts are used to calculate the Mean Failure Height the point at which 50% of the test samples will fail under
the impact.