Gardner Impact ASTM D4226, D5420

Scope:
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.

Test Procedure:
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.

Specimen size:
For optimum results using the staircase method, a minimum of 30 test samples are necessary. Any flat specimens can be tested - the preferred test sample is a 100mm (4") disk or plaque.

Data:
Mean Failure Height in cm (inches)
Mean Failure Energy in kg-cm (in-lb) 

**Please note that this test description is intentionally generic in nature and aimed at providing a descriptive summary to enhance test understanding. Standards can be obtained from appropriate standards authorities.