Elastomers Industry Guide for Material Testing
The Elastomers category also includes rubber and fluoro-polymers. Rubber products are manufactured similar to plastic, however elastomers differ from plastics in a few key areas.
Rubber is a highly elastic material and is able to return to its original shape after being stretched or compressed. Most rubber and elastomeric materials generally do not exhibit a high ultimate tensile strength.
Modulus of Elasticity (MOE) - is a measurement of a material's resistance to elastic deformation. MOE is also commonly referred to as the elastic modulus or Young's modulus. The modulus of elasticity is given by the slope (aka derivative) of the stress/strain curve in the elastic zone of a tensile test. The elastic deformation zone is defined as the region where a material can be deformed and still return afterwards to its original size and shape.
The Modulus of Rupture (MOR) - is the maximum amount of stress that a material can withstand before it yields and breaks. MOR is also referred to as the bend strength, flexural strength, or fracture strength. The modulus of rupture is the peak value seen just before the bend testing specimen breaks.
Introduction to ASTM Testing for Rubber
ASTM D412 - Rubber Tensile Testing is the most common procedure for testing elastomers. A small, reduced section specimen is pulled apart at a constant rate of speed. For more information on the ASTM D412 specimen sizes, visit our page on cutting dies. An extra tall tensile testing machine is typically used since these types of samples tend to have high elongation. Some quality professionals will use a shorter sample size in order to avoid having to purchase a larger machine. For those who do need an extra tall system, Universal Grip recommends using a dual column testing machine for any tests with travel over 1 meter or 36". The extra tall dual column design is much more robust and reliable compared to a single column machine. Self-tightening roller grips or pneumatic grips are used for testing elastomers. These grips create striction on the sample which prevents it from slipping as it thins out during the test.
ASTM D624 - Elastomer Tear Testing uses a "V" shaped sample. The sample is pulled from both sides by either roller grips or pneumatic grips. Vise grips can also be used if there is not much deformation of the sample before it tears. Tear testing is usually a low force test, so it may be necessary to downsize on the load cell to get better readings. Universal Grip offers cutting dies for D624 specimens.
ASTM D395 - Compression Set under Constant Deflection has two methods, A and B. Method A uses a spring loaded device to create the constant deflection. This method is not used as often because the spring can weaken over time which slightly alters the results. Method B is much more commonly seen and does not use a testing machine. The fixture is designed with several cavities for the disc shaped samples. The samples are loaded into the cavities and the nuts are tightened to induce the compression. The samples are then left for 8 to 24 hours. For more info please see our full write up.
Universal grip offers the Graphwork 6 software for Galdabini's full line of universal testing systems. The software is flexible and easy to use and can come pre-loaded with all of your required ASTM tests. UGC and Galdabini's engineers will ensure that your machine conforms to ASTM standards and that you are testing properly. The software also has some powerful backend database tools for exporting results to Laboratory Information Management Systems (LIMS). Software training and well-documented manuals are included with every machine.
Mechanical Device for Elongation Testing
The device pictured on the right is an economical solution for gathering elongation measurements from ASTM D412 type rubber specimens. The system is turned by a wrench and the measurement is taken manually using a ruler or caliper. This design can test up to 3 samples simultaneously.