ASTM D412 Tensile Strength Properties of Rubber and Elastomers

  

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ASTM D412 (D 412) is the most widely referenced testing standard for measuring the tensile properties of thermoset rubbers and thermoplastic elastomers. ASTM D412 covers two test methods, A and B. The more popular method is A, which can be performed using a universal testing machine also known as a tensile testing machine or tensile tester. This is a general guide intended to help you understand the basic test procedure and the different system configurations you can use to perform this test. When you are ready to test your products or materials to this standard, we recommend purchasing and referencing the official ASTM D412 document.

1. Cut or injection mold your material into a "dumbbell" shaped specimen.

2. Load the specimen into tensile grips.
3. Attach the optional extensometer to the sample
4. Begin the test by separating the tensile grips at a speed of 20 inches per minute
5. End the test after sample break (rupture)

Analysis:

1. Stress at user-specified extension or elongation
2. Tensile Yield Stress
3. Tensile Yield Strain
4. Tensile Strength at Rupture
5. Elongation at Rupture

Test report showing elengation, generated with MTESTQuattro

Test report showing max stress, generated wtih MTESTQuattro

Equipment:

ADMET provides a wide range of system configurations that meet ASTM D412 requirements. An advanced configuration would include an eXpert 2600 dual column testing machine or an eXpert 7600 XLT (a single column testing machine with extended vertical testing space), an extensometer for more accurate elongation measurement, and MTESTQuattro, an advanced PC based testing machine controller with built-in analysis and reporting capabilities. The video below shows a fully equipped eXpert 7600 XLT single column system performing ASTM D412.

A more affordable solution can be provided  with a standard eXpert 7600 testing machine without an extensomter and equipped the eP2 Digital Controller, a more basic standalone touch-panel controller. The video below shows our most affordable system configuration performing ASTM D412.

The minimum requirements for a system capable of performing ASTM D412 are:

1. Universal testing machine (tensile testing machine) with these minimum specifications:
A. Servo-controlled to keep a constant rate of speed during the test (+/- 2 inches/min)
B. At least 30 inches of crosshead travel or more for high elongation materials
C. Most small and common 1kN (225 pound) load capacity machines will work for the loads of the materials tested to this specification

All of our eXpert 2600 series dual column machines meet these requirements, and it is also common to use our single column eXpert 7601 XLT with 53 inches of crosshead travel.

eXpert 7601 with MTESTQuattro (left) eXpert 2610 with extensomter and MTESTQuattro (right)

2. An extensometer is optional but recommended. We recommend one for two reasons. First, dumbbell specimens do not have uniform widths which cause errors when both the wide and narrow sections of the dumbbell shaped specimen elongate at different rates. Secondly, elongation is usually an important design characteristic of rubbers and elastomers so an extensometer can be used to improve accuracy of the measurement.

eXpert 2610 with extensomter and MTESTQuattro (left) eXpert 7600 XLT with extensomter and MTESTQuattro (right)

3. Software or suitable electronics are required to operate the machine and to take the measurements. A basic system equipped with the eP2 digital controller will provide the raw data, and stress-strain charts. Using these sources of data, you can determine and calculate all of the analysis listed above. However, fully PC based systems have the capability to calculate all of these automatically. For example, our MTESTQuattro testing software has built in support for ASTM D412 and all of these calculations are provided immediately after performing the test.

MTESTQuattro (left) eP2 Digital Controller (right)

4. Tensile grips hold your specimen during the test as it is being pulled apart. Quite often, hard specimens are difficult to hold properly as premature breakage and slippage can be common. However, rubbers and elastomers usually lend themselves to being easily held in a variety of grip designs such as manual vise grips, pneumatic grips, wedge grips, or eccentric roller designs. The most common and easy to use grips are manual vise or pneumatic grips with rubber coated or serrated insert faces.

(From left to right) Pneumatic grip, wedge grip, eccentric roller grip