ASTM D4226, D5420 Gardner Impact Test

Scope:

Falling Dart Impact Test by ASTM D4226 and ASTM D5420 is a standard test method in plastic industries for testing impact resistance of flat, rigid plastic materials employing a striker hit by a falling weight. This test is also known as the Gardner impact test. The ASTM D4226 and ASTM D5420 test is needed for products that are damaged by some extent of impact force. The Falling Dart Impact Test is specifically used to establish quality standards for resistance to impact surface defacement and penetration of the underlying layer of construction materials, such as plastic materials, fibreglass, resins, sheet metals, etc. It also tests the ‘impact resistance’ of several types of organic coatings.  

Test Procedure:

The ASTM D4226 and ASTM D5420 test sample is kept on a base plate over an opening of the measured diameter. A specific weight impact striker sits on top of the test sample with a nose of a specified radius touching the center of the test sample. The drop height, drop weight, and test result (pass/fail) are recorded. “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 can be determined. 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 is calculated from those 20 impact results, at which 50 percent of the test samples failed.

Specimen size:

For optimal results using the Bruceton method, 20-30 test samples are necessary. Specimens tested are flat. The best test sample is a 100 mm (4 inches) disc.

Data:

Mean Failure Height is given in cm (or inches).

Mean Failure Energy is given in kg-cm (or in-lb).

Conclusion:

Hence, ASTM D4226 and ASTM D5420 is a standard test method for evaluating the impact strength or toughness of a plastic material.