Impact Resistance of Plastic Film
Impact Resistance of Plastic Film: Understanding the Free-Falling Dart Method ASTM D1709, ISO 7765-1
Plastic films are widely used in various industries, including packaging, construction, and agriculture. The ability of plastic films to withstand impact is crucial in ensuring their quality and suitability for various applications. The free-falling dart method is a commonly used test to evaluate the impact strength or toughness of plastic films. This method is standardized by ASTM D1709 and ISO 7765-1 and is widely used by manufacturers and testing laboratories.
Scope of the Test
The free-falling dart method evaluates the impact resistance of plastic films using a single dart configuration and a single drop height, while varying the weight of the dart. The test results can be used to assess the quality of the plastic film or compare different products for their end-use suitability. The test can be used for quality control purposes in manufacturing or to ensure that a plastic film meets specific standards and regulations.
Test Procedure
The free-falling dart test involves clamping the plastic film securely in a pneumatic ring at the base of a drop tower. The mounting bracket is adjusted to the appropriate drop height, depending on the expected impact strength of the test sample. There are two test methods, A and B, that specify different dart sizes and drop heights.
Method A involves using a dart with a 38 mm (1.5") diameter and dropping it from a height of 0.66 m (26")
Method B involves using a dart with a 51 mm (2") diameter and dropping it from a height of 1.5 m (60")
The test is conducted on a minimum of 30 specimens that are cut to 230 mm x 230 mm (9" x 9") specimens. The initial weight of the dart is determined based on the expected impact strength of the plastic film. The test specimen is then impacted, and the drop weight and test result (pass/fail) are recorded using the Bruceton Staircase method.
The Bruceton Staircase method is a statistical method used to analyze the data generated by the free-falling dart impact test. It is a step-by-step procedure that involves increasing or decreasing the drop weight of the dart, depending on whether the test specimen passes or fails.
The Bruceton Staircase method is used to determine the Impact Failure Weight (IFW), which is the weight of the dart at which 50% of the test specimens will fail under the impact. The IFW is a critical parameter used to evaluate the impact strength or toughness of plastic films.
The method involves conducting a series of 20 to 25 impacts on the test specimen. If the test specimen passes, the drop weight of the dart is increased by one unit, and if the test specimen fails, the drop weight is decreased by one unit. This process is repeated until a specific number of passes and fails are obtained. The Bruceton Staircase method involves plotting the data obtained from the impacts on a graph and calculating the IFW using statistical methods.
Conclusion
The free-falling dart method is a standardized test that evaluates the impact resistance of plastic films using a single dart configuration and varying the weight of the dart. The test is widely used in the manufacturing industry and testing laboratories to assess the quality and suitability of plastic films for various applications. The test results can be used for quality control purposes or to compare different products for their end-use suitability. By understanding the data generated by this test method, manufacturers can ensure that their plastic films meet specific standards and regulations and provide high-quality products to their customers.