During ASTM D882 testing, specimens are pulled in tension until failure. The crosshead speed is dependent on the length of the specimen and can be calculated by multiplying the initial grip separation (length of the specimen) by the initial strain rate in mm/mm x min. The initial strain rate is conditional on the maximum elongation of the specimen at break. Because plastic films and sheeting tend to be highly elastic, higher crosshead speeds are commonly required. One critical factor in testing to ASTM D882 is using an appropriate preload. Thin film specimens are usually relaxed and not taut when loaded into grips for testing. A preload, which can be easily configured in Bluehill Universal testing software, helps to remove any slack in the specimen prior to recording data during testing, ensuring that results are accurate and repeatable.
This test is meant for specimens uniform to within 10% of the thickness over the length of the specimen between the grips. Thicker specimens approaching the 1 mm thickness limit must be uniform to within 5%. Specimens need to be between 5.0 and 25.4 mm wide, and at least 50 mm longer than the grip separation used during testing. The standard specimen gauge length for testing is 250 mm. However, if this is not possible, then a minimum specimen length of 100 mm (50 mm gauge length) is acceptable as long as it is established that this does not affect the results. If the sample is of isotropic material, the standard requires at least five specimens to be tested from each sample. If the sample is suspected of being anisotropic, however, then at least ten specimens must be tested, five along their long axis, and five along the supposed anisotropic axis. Furthermore, specimens used to determine modulus cannot be used to determine tensile strength or any other tensile properties, which means that anyone testing to ASTM D882 would be wise to produce a large number of specimens in order to appropriately measure all of the relevant properties.