One of the most common specifications that our customers follow is ASTM D882 which is the Standard Test Method for Tensile Properties of Thin Plastic Sheeting. This test is very similar to the common ASTM D638 test whereby plastic material is pulled until in breaks in order to measure elongation, tensile modulus, tensile yield strength, and tensile strength at break. However, it is designed specifically for thin sheeting and film less than 1 mm (0.04″) thick.
The nice part about ASTM D882 is that the specimens are rectangular strips of film and are not “dumbbell” or “dog bone” shaped. The flat geometry of the specimens and the typical characteristic of films having high elongation allow most users to avoid using an extensometer which allows them to reduce the cost of the testing system and simplifies their testing regimen.
The two main things to keep in mind in regards to equipment are the height of the testing machine and having grips designed to hold the thin film correctly. We always recommend our eXpert 7601 single column test machine with 29″ of crosshead travel for films with less than 300% elongation and our 53″ model for really high elongation films that elongate up to 900%. The grips we recommend are pneumatic vise grips with rubber coated inserts. The rubber coated inserts help to keep the film from prematurely breaking at the grip edge, and in combination with the constant pneumatic pressure the film is prevented from slipping out of the grips during the test. We use foot pedals to allow the operator to open and close the grips with their feet because thin films usually require both hands to line everything up properly. If you have a 30″ crosshead travel machine, the grips and load cell will take up about 12″ of that travel. If you use a 4″ gage length it will take up another 4″ of the travel. This leaves 14″ of testing travel which will be fine for materials with less than 350% elongation (14″ crosshead travel / 4″ original gage length = 3.5 * 100% = 350%) A 54″ crosshead travel machine is better suited for materials that have elongation up to 950%.
We are always available to answer your questions. Should you have any questions, please feel free to call us @ 800-667-3220 or visit our website for more information.