Tensile Strength (TS)

Ultimate tensile strength (UTS), commonly referred to as tensile strength (TS) or maximum strength, is the maximum load that a material can withstand in a tensile or pulling action before failure or fracture. The maximum load that vulcanized rubber or thermoplastic elastomer can withstand before failure is its ultimate tensile strength.

Importance:

Tensile testing is used for product quality control and to determine the effects of chemical or thermal exposure on elastomers. The most crucial factor is the elastomer's ability to maintain its physical properties, rather than the exact values of tensile strength, elongation, or modulus.

Measuring Tensile Strength:

Tensile strength is defined as the load measured as a force per unit area. Generally, the test involves taking a small sample with a constant cross-sectional area and then stretching the material using a tensile tester (tensiometer) under a constant stress change (change in length of the sample divided by the original length of the sample) until the sample breaks.

There are three typical types of tensile strength:

  • Yield Strength: The load that can be applied to a material before permanent deformation occurs. This is not a sharply defined point. Yield strength is the load that will cause a permanent deformation of 0.2% of the original dimension.

  • Maximum Strength: The maximum load that a material can withstand.

  • Fracture Strength: The coordinate of the load on the load-stress graph at the point of fracture.

The tensile strength (ASTM D412-98a) of a material is determined by one of two measurement methods, which do not always yield identical results, as follows:

Test Method A:

  • Samples in the shape of a bell with a straight cross-section – The test samples are either injection molded or cut from flat sheets with a thickness of no less than 1.3 mm (0.05 inches) and no more than 3.3 mm (0.13 inches).

Test Method B:

  • Samples in the form of cut rings – The samples for testing are created by cutting rings from sheets or tubes. In both cases, dimensions, etc., are defined according to ASTM specifications.

Calculating Tensile Strength:

The calculation of the tensile strength (TS) of a material is performed using the formula:

[ TS = \frac{F(BE)}{A} ]

Where:

  • ( TS ) = Tensile strength, the load at break, MPa (lbf/in²)

  • ( F(BE) ) = Force at break, MN (lbf)

  • ( A ) = Cross-sectional area of the sample at zero stress, m² (in²)