Tensile test

The tensile test is a central procedure in mechanical material testing. In this process, a standardized specimen is subjected to uniaxial tensile loading to characterize material behavior under tensile stress – from the initial elastic elongation to the point of fracture. Many characteristic values found in data sheets for metals, plastics, and elastomers are derived from the tensile test.

Test Setup and Procedure

For the tensile test, a specimen (e.g., a shoulder-type or standardized dumbbell-shaped specimen) with a defined cross-section and gauge length is clamped into a testing machine.

• The machine pulls the specimen apart at a controlled speed.
• During the test, tensile force and change in length are continuously measured.
• Tensile stress is calculated from the force and initial cross-section, while strain (elongation) is calculated from the change in length and initial length.

The result is a stress-strain curve, which shows the complete progression from the initial linear, elastic deformation through plastic yielding to the final fracture (in elastomers, this is primarily a highly non-linear elastic progression up to the elongation at break).

Typical Characteristic Values from the Tensile Test

Depending on the material and the applicable standard, the following values are typically determined:

• Modulus of Elasticity (E-modulus) – the slope of the linear, elastic region of the curve.
• Yield point or 0.2% offset yield strength (for metals and thermoplastics).
• Tensile strength (maximum tensile stress before fracture).
• Elongation at break – the strain at the moment the specimen fractures.
• For elastomers, additionally: Stress at 100% / 300% elongation (often referred to as Modulus 100 / 300).

As described in classical materials science, the elongation at break consists of uniform elongation and necking elongation, and depends on the material as well as the specimen shape and gauge length.

Significance for Elastomers and Seals

In elastomer technology, the tensile test provides vital data for:

• Seals and O-rings (elongation at break, tensile strength, safety against tearing).
• Profiles and molded parts (load capacity during assembly, elongation paths, notch sensitivity).
• Vibration and bearing elements (relationship between stiffness and geometry).

These characteristic values directly influence the design of sealing points, the selection of the appropriate elastomer material (e.g., NBR, EPDM, FKM), and the dimensioning of cross-sections – especially wherever elongation, recovery behavior, and tear resistance are decisive factors.

Synonyms / related terms: Tensile testing, tensile test according to DIN / ISO, uniaxial tensile test, mechanical material testing in tension.