If the sample is of isotropic material, the standard requires at least five specimens to be tested from each sample. 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. The standard specimen gauge length for testing is 250 mm. 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. Thicker specimens approaching the 1 mm thickness limit must be uniform to within 5%. This test is meant for specimens uniform to within 10% of the thickness over the length of the specimen between the grips. 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. Thin film specimens are usually relaxed and not taut when loaded into grips for testing. 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. The initial strain rate is conditional on the maximum elongation of the specimen at break. 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. Learn More About Electric Vehicle TestingÄuring ASTM D882 testing, specimens are pulled in tension until failure. Additionally, as is the case for many other thin film materials, separator film is anisotropic and so is recommended to be tested in multiple different cutting/testing directions. Testing these materials in accordance to ASTM D882 can be very beneficial for quality control checks as well as in R&D when trying to determine the optimal separator film solution. Safer and stronger separator material more effectively prevents contact between the anode and cathode, while thinner material helps reduce the weight of each battery and improve energy density. The most common material used for separator film is polyolefin, a polymer film that is strong enough to withstand the winding operation during assembly as well as uneven plating of lithium on the anode due to extensive use. Separator films are a critical part of lithium-ion and other liquid electrolyte batteries that separate the anode and cathode. Though ASTM D882 is not an official standard for testing EV battery separator films, this standard is being modified to evaluate the mechanical properties of these materials. Separator Film Testing for Electric Vehicle Batteries
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