How to Perform a Tear Strength Test on Vulcanized Rubbers and Thermoplastic Elastomers
Written by Kayla Thackeray
ASTM D624 is a common test method used to determine the tear strength of vulcanized rubber and thermoplastic elastomers. Due to the specimen shapes often used, this test is sometimes called a trouser, angle, or crescent test. This guide is designed to introduce you to the basic elements of an ASTM D624 test and will provide an overview of the testing equipment, software, and specimens needed. However, anyone planning to conduct ASTM D624 testing should not consider this guide an adequate substitute for reading the full standard.
Is ASTM D624 The Right Standard for Me?
ASTM D624 provides similar results to ISO 34, another common test that measure the tear strength of elastomeric materials. Though the ASTM and ISO organizations are currently working toward diminishing the differences between these two standards, the results cannot yet be considered comparable, and care must be taken to ensure the correct test standard is being used for a given application. ASTM D624 is intended to measure tearing strength only: anyone seeking to determine the tensile properties of elastomers should refer to ASTM D412.
Testing to ASTM D624 can be performed on a tabletop (dual column) or single column universal testing system due to its low crosshead travel. Laboratories that test to ASTM D624 are typically also running tensile tests to ASTM D412, and for the sake of convenience will often use the same test system for both. Because the maximum force applied during elastomer tear testing is significantly lower than the maximum force applied during elastomer tensile testing, load cells of differing capacities may be used. However, a 2580 series load cell can accommodate both types of tests for most applications because of their exceptional force range and accuracy. Instron’s 2580 series load cells are designed for 6800 Series testing systems.
Software is a critical element of any testing system and can greatly simplify the testing process. Bluehill Universal comes pre-loaded with all of the most common ASTM and ISO standards, including ASTM D624, ASTM D412, and ISO 34.
The best types of grips to use for ASTM D624 are grips that supply a constant pressure like pneumatic side action or self-tightening roller grips. Both of these grips will prevent slipping during the test and will allow for quick specimen insertion. For some materials, basic screw action grips can be used. An important element of ASTM D624 testing is to align specimens vertically and in the same position for each test. Because tear tests are known to produce wide variation in results, it is important to eliminate as many variables as possible. Pneumatic side action grips have the advantage over other grips in that they help to align the specimen. It is also important to pair the grips with jaw faces to make visual alignment easier: jaw faces should be the same width as the specimen.
In order to properly align your specimen, set the initial position of the crosshead such that the top and bottom edge of the specimen line up with the top edge of the jaw face on the upper grip, and the bottom edge of the jaw face on the lower grip. This will ensure that the center of the specimen is aligned with the center of the grip separation.