ASTM D412 specifies the test conditions for determining the tensile properties of molded and die cut elastomers. Because of the extensibility that rubbers and elastomers exhibit, extensometers are usually required to accurately measure elongation or stretch while loading is applied.
Traditionally, long travel contact-style extensometers have been used to test these materials. Non-contacting extensometers such as the Standard Video Extensometer (SVE) have more recently proven to be as effective, if not more effective in some cases. When materials are very delicate, contact extensometers may induce premature failures. In addition, the weight of a contact extensometer may influence results. Non-contacting extensometers are a suitable solution for materials similar to vulcanized rubber and thermoplastic elastomers, in addition to most materials tested in accordance to ASTM D412.
In addition to extensometer selection, the proper grip type and grip face are required to successfully test elastomeric materials. Typically, pneumatic side-acting grips with serrated or rubber coated faces are the preferred gripping configuration. The constant gripping force prevents specimen slippage when specimens are elongated. Other self-tightening style grips, such as roller grips, have also proven to be adequate for elastomeric materials.
We recommend reading and reviewing ASTM D412 in order to fully understand the test setup, procedures, and results requirements.