Tensile strength

Tensile strength describes the maximum tensile stress a material can withstand before failing. It indicates how resistant a material is to elongation stress – in other words, how much tensile load it can absorb before it tears or undergoes unacceptable plastic flow.

In data sheets, tensile strength is usually specified in N/mm² (which is equivalent to MPa).

Determination in the Tensile Test

Tensile strength is determined using a tensile test:

• A standardized tensile specimen (e.g., a shoulder-type or dumbbell-shaped specimen) is subjected to uniaxial tensile loading.
• The testing machine increases the tensile force uniformly until the specimen breaks.
• The maximum tensile force reached (Fmax) is divided by the original cross-section (A0) of the specimen.

The tensile strength is calculated as follows:

Tensile strength = Fmax / A0

where:

Tensile strength = Tensile strength (in N/mm² or MPa)

Fmax = Maximum tensile force reached during the test (in N)

A0 = Original cross-section of the specimen (in mm²)

The result is incorporated into the material's stress-strain curve and marks the point of maximum stress before failure or significant yielding.

Material Behavior – Metals, Plastics, Elastomers

• Metals usually show an elastic range followed by plastic deformation. Tensile strength is the maximum stress reached before necking and fracture occur.
• Thermoplastics can often be stretched further after exceeding their tensile strength while the cross-section tapers significantly; here, tensile strength marks the maximum stress level before failure.
• Elastomers (e.g., NBR, EPDM, VMQ) behave in a highly non-linear elastic manner. In this context, one often refers to tear strength or breaking stress, which is the stress at the moment the specimen tears. In many elastomer data sheets, this value is colloquially also referred to as tensile strength.

Context is always key: for the design of seals and molded parts, elongation at break, tear resistance, and compression set are just as critical as tensile strength.

Significance in Sealing Technology

In elastomer and sealing technology, tensile strength provides information regarding:

• Safety against tearing during the installation of O-rings and sealing lips.
• The load capacity of profiles and molded parts, e.g., under tensile and bending loads.
• The behavior of diaphragms and hoses subjected to tension or internal pressure.

A sufficiently high tensile strength – combined effectively with high elongation at break – ensures that seals, profiles, and elastomeric molded parts function reliably and do not fail prematurely, even during installation, stretching, or under vacuum/pressure loads.