ASTM D882 is a common standard that is used to determine the tensile properties of plastic film or sheeting. The tensile properties include tensile strength, yield strength, yield strain, strain at break, and modulus of elasticity. Due to the flexible, delicate nature of these plastic specimens, both gripping and strain measurement can be a challenge.
The challenges of testing to the standard are:
- Specimen gripping
- Accurate strain measurement
- Reporting calculations in compliance with the standard
Instron's Solution:
- Specimen gripping – Rubber grip faces that match the width of the gripped or tabbed end of the specimen are commonly used for testing. The most common face size for this type of material is 25 mm x 25 mm (1 in x 1 in). The matching width allows for ease of specimen alignment, which is critical for good breaks and accurate test results. Pneumatic side action grips provide adjustable inlet air pressure to ensure the specimens can be clamped sufficiently throughout the test while preventing premature failure.
- Accurate strain measurement – While extensometry is not required by the standard, using an extensometer can result in the most accurate strain measurement. Non-contacting video extensometry is usually the best solution, as typical clip-on extensometers weigh down the specimen, while knife edges tear at the specimen - both affecting test results. Video extensometers, such as the Advanced Video Extensometer 2 (AVE 2), allow for ease of marking with paint pens and marking templates, which are provided with the instrument.
- Reporting calculations in compliance with the standard – Instron's Bluehill® Universal testing software has advanced pre-built methods available with pre-configured plastic specific calculations helping to ensure compliance. Using features such as an appropriate preload is critical for achieving accurate, repeatable results. A preload eliminates the compressive forces on a specimen that often occur when initially placed into grips.
It is important to review ASTM D882-12 in order to fully understand the test setup, procedure, and results requirements. For more information please visit our Definitive Guide to ASTM D882.