Bend don’t break. It’s a phrase used in many walks of life. The defense of a football team that gives up yards but doesn’t allow a touchdown. The student that does just enough to pass the class despite failing a midterm. The expression can also refer to tensile properties of plastics. Sort of. ASTM D882-18 Standard Test Method for Tensile Properties of Thin Plastic Sheeting is a standard that looks to specifically dive into the delineation of characteristics in plastics relating to tension.
These characteristics are found through a process called tensile testing. Generally, the subject is exposed to a certain amount of tension until it can no longer exist in its original form. Using a mechanical device with a stationary part and a moveable part, both with grips to hold the specimen, the plastic is pulled. In this case, unlike that football team and student, it bends (or more accurately stretches) until it breaks. Don’t worry though. That’s the point.
From this process numerous traits of the material being tested can be found. According to ASTM D882-18, these properties include tensile stress, elongation, and modulus. Amongst other things, these kinds of characteristics “can be utilized to provide data for research and development and engineering design as well as quality control and specification.”
It’s important to note that ASTM D882-18 refers directly to certain thickness of plastics. ASTM D888-18 refers to plastics “in the form of thin sheeting and films (less than 1.0 mm (0.04 in.) in thickness).” Unearthing the same properties in plastics that are thicker than 1.0 mm or 0.04 inches can be found using the test procedures found in ASTM D638-14: Standard Test Method for Tensile Properties of Plastics.
ASTM D882-18 revises ASTM D882-12. Some of its changes of note are:
- “An added Section 4 Summary of Test Method.” As well as a renumbering of the sections that follow Section 4.
- Explains “that 10% uniformity of thickness is based on average thickness.”
- Clarifies that the user should take three measurements for the cross-sectional area instead of the vaguer several.
- “Subsection 12.2: Revised to use average width of specimen as opposed to minimum to stay consistent with how stress and modulus are calculated.”
ASTM D882-18 Standard Test Method for Tensile Properties of Thin Plastic Sheeting is available at the ANSI Webstore.