Gardner Impact ASTM D4226
Falling Dart Impact (Gardner Impact) ASTM D4226, ASTM D5420
Falling dart impact, also referred to as Gardner impact, is a widely accepted method for determining the impact strength or toughness of plastic materials. This test is commonly employed to determine the most suitable materials for impact-related applications, as well as to analyze the impact properties of plastic materials after being subjected to secondary finishing processes or environmental factors.
Test Procedure
To conduct a falling dart impact test, a test sample is placed on a base plate over an opening of predetermined diameter. A weight, which is guided by a tube, is lifted to a predetermined height, and then released to fall onto the top of an "impactor" with a nose of specified radius that is in contact with the center of the test sample. The drop height, drop weight, and test result (pass/fail) are recorded. The most common analysis method is the "Bruceton Staircase" method, which involves using several samples to bracket the pass/fail energy level, followed by a series of 20 impacts. If the sample passes, the drop height is increased by one unit, and if it fails, the drop height is decreased by one unit. The results from the 20 impacts are then used to calculate the Mean Failure Height, which is the height at which 50% of the test samples will fail under the impact.
Specimen size
For the "Bruceton Staircase" method, a minimum of 30 test samples are required. Any flat specimens can be used, but the most preferred specimen is a 100mm (4") disk or plaque.
Data
The falling dart impact test provides two types of data: Mean Failure Height in centimeters (or inches) and Mean Failure Energy in kg-cm (or in-lb). The Mean Failure Height is the most common analysis result, and it indicates the height at which 50% of the test samples fail. The Mean Failure Energy is calculated by multiplying the Mean Failure Height by the weight of the falling dart. This value indicates the amount of energy required to fracture the material.