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. This shape means that you don’t need to use an extensometer to measure the elongation as the system’s built in crosshead displacement indicator is sufficient. This reduces the cost of the testing system and simplifies the testing process.
The video below shows an ADMET eXpert 7601 Universal Testing System performing the ASTM D882 tensile and elongation test. This system also performs tear, puncture, peel, cling, and coefficient of friction tests.
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 recommend our eXpert 7601 single column test machine with 29″ of crosshead travel for films with less than 300% elongation and our eXpert 7601 XLT model that has 53″ of crosshead travel model for really high elongation films that elongate up to 900%. The grips we recommend are pneumatic or manual vise grips with rubber coated inserts. The rubber coating prevents the film from prematurely breaking at the grip edge and also keeps it from slipping. Pneumatic grips are used as a matter of convenience when testing but are not required. You can open the pneumatic grips with finger toggles or foot pedals. Foot pedals are really easy to use and allow the operator to use both hands to load the sample. 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%.