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ASTM D412 | Plastics and Elastomers | Tension Testing

ASTM D412 covers the testing of tensile properties of thermoset rubbers and thermoplastic elastomers. The specification describes two test methods: A and B. Method A is common and can be performed on a universal testing machine. The testing systems recommended for this test include the eXpert 2600 Dual Column Testing Machine and the eXpert 7600 Single Column Testing Machine. If you are going to perform this test, you should read the entire specification from ASTM. This is a quick summary to decide if ASTM D412 is right for you and to point out what equipment you need to perform the test.

MTESTQuattro Controller & Software

MTESTQuattro® is an advanced materials testing system for servo-hydraulic and electromechanical testing machines. Its unique design consists of a PC-based application program and an easy-to-install external interface box which makes MTESTQuattro well suited for new and retrofit installations. It features a state-of-the-art digital controller for performing accurate and repeatable tests according to ASTM and ISO standards. MTESTQuattro is capable of performing all types of tests including tension, compression, creep, fatigue, friction, flexure, relaxation, peel, shear and tear tests. Additionally, the software includes a “go home” feature, allowing the testing machine to easily return to its original positioning after a break. Being a comprehensive program, users can easily create and recall ASTM compatible and user-definable test procedures and generate test reports that include a stress vs. strain curve and a summary of calculated mechanical properties. MTESTQuattro’s base configuration consists of load, crosshead position, axial strain, transverse strain and auxiliary input channels with options for three additional auxiliary input channels and servo control. The input channels are compatible with all force measuring; contacting and non-contacting strain measuring devices which make it possible to measure key mechanical properties such as elastic modulus, yield strength, ultimate strength and elongation.

Pneumatic Grips

Pneumatic grips recommended to run ASTM D412 testing are available as either wedge or vise types. They allow for rapid sample changes and constant clamping force. Plastics, metals, fabrics, films, ceramics, and many other types of samples can be held in a pneumatic grip. Once the pressure is set, the air pressure will remain constant throughout the test. This prevents slippage while allowing testing of thinner materials that might break in the grip faces if the inserts were clamped too tight. Test specimens can be inserted in the grips positioned symmetrically and in axial alignment with the direction of testing. This removes the bending strains that can skew data and is particularly useful when tests are performed in high or low temperatures using an environmental chamber where internal temperature changes need to be avoided while setting up specimens in the grips. In addition, compared to hydraulic grips, the use of pneumatics is cleaner as pneumatics transmits power using air pressure instead of using a liquid. Consequently, setting up tests using pneumatic grips is much quicker.

Other recommended ASTM D412 testing grips include self-tightening eccentric roller grips and wedge grips.

Long Travel Extensometer

ADMET offers long travel extensometers up to 1,100mm (43.3in) travel range that allow for easy travel directly on the specimen. Axial extensometers provide strain data by clamping onto the specimen with their knife edges and measuring the displacement in length as load is applied and the specimen is pulled. Stress vs. strain graphs are among the most common analyses on a tensile test report as they can be used to study multiple mechanical properties based on the specimen’s deformation profile and its reaction under applied load. EX-700CT and EX-110CT extensometer clamps move freely with the specimen and are counterbalanced in order to ensure that the weight of the clamps has no effect on the displacement of the specimen. ADMET long travel extensometers are recommended for use with ASTM D412 specimens and have the ability to extend to gauge lengths adjustable between 20 to 80mm (0.79in to 3.15in).

Environmental Chamber

Specimens tested under the D412 requirements often require specific environmental conditions. Changing the temperature in the testing space is made feasible by adding an environmental chamber to a universal testing machine. ADMET offers standard and custom environmental chambers, which come with their own controller and can also be set up to communicate with MTESTQuattro.

Chambers come with slide rack rails that allow the chamber to be pulled out of the machine when not in use. Grips and fixtures are manufactured with special materials that can withstand custom temperatures. The specimen is secured in place to minimize contact with the sides of the chamber, and the chamber contains vents to remove fumes from the system. Extensometers, deflectometers, and other accessories can also be added at the customers disposal. Various designs of extensometers exist for high or low temperature testing applications. Special extensometers measuring strain through the walls of the chamber can withstand temperatures up to 1200°. The 4-glass-layered door window is heated to reduce icing and condensation during low temperature testing. This feature also acts as a viewing door, and grips may be oriented so that the specimen can be observed in the proper manner.

Prior to conducting ASTM D412, it is important to read the entire specification in the relevant ASTM publication.

ASTM D412 | Plastics and Elastomers | Tension Testing

  1. Cut your material into a “dogbone” shaped sample.
  2. Load the sample into a pair of tensile grips suitable for elastomers and attach your  extensometer (if you have one).
  3. Begin the test by separating the tensile grips at a rate specified in the standard and run until sample break (rupture).
Calculations:
  • Stress at User-Specified Extension or Elongation
  • Tensile Yield Stress
  • Tensile Yield Strain
  • Tensile Strength at Rupture
  • Elongation at Rupture

ASTM D412 | Plastics and Elastomers | Tension Testing

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