How to Perform a Tensile Strength Test on Elastomers According to ASTM D412
ASTM D412-2015 describes a method for determining the tensile stress-strain properties of vulcanized and thermoplastic rubbers. The standard has two methods, A and B, depending on the specimen geometry being tested. Method A refers to the use of dumbbell shaped specimens, while method B refers to ring shaped specimens. The properties which can be determined are tensile strength, elongation at break, stress at a given elongation, and yield point. The measurement of stress and strain at yield applies only to some thermoplastic rubbers and certain other compounds.The challenges of testing to this standard are:
- Accurate strain measurement at high elongations
- Secure gripping of varying specimens
- Reporting calculations in compliance with the standard
- Accurate Strain Measurement – Advanced strain solutions for contacting and non-contacting strain measurement. While extensometers are not required by the standard, a strain measurement is recommended for the most accurate and repeatable results. A non-contacting solution like the Standard Video Extensometer (SVE 2) is ideal for all specimen types while contacting solutions such as the XL long travel extensometer is more specifically suited for robust specimens.
- Secure Gripping of Varying Specimens – Varying gripping options, including pneumatic side action grips and mechanical self-tightening grips, ensure no slippage occurs despite specimen thinning. The O-ring fixture is designed specifically to comply with method B of the standard.
- Reporting Calculations in Compliance with the Standard – Instron Bluehill® testing software has advanced pre-built methods available with pre-configured elastomer specific calculations.
It is important to review ASTM D412-15 in order to fully understand the test setup, procedure, and results requirements.For more information on ASTM D412 please view our Definitive Guide to ASTM D412 Tensile Testing of Elastomers.