What is tensile strength?
The tensile strength is a mechanical characteristic value that indicates the maximum tensile stress that a material, e.g. elastomers such as NBR, EPDM, FKM or natural rubber (NR) before the material tears. Tensile strength describes the resistance to a tensile load and is crucial for assessing the load-bearing capacity and service life of components. It is specified in megapascals (MPa) or newtons per square millimetre (N/mm²).
Measurement and definition of tensile strength
The tensile strength is determined using standardised test methods (e.g. DIN 53504 or ISO 37). In a tensile test, a standardised sample is stretched at a constant low speed (quasi-static) until it breaks. The tensile strength is calculated as the ratio of the maximum tensile force acting at break to the initial cross-section of the unloaded sample:
- Tensile strength = maximum force/cross-sectional area
- High tensile strength values mean that the material can withstand high mechanical forces without failing.
Factors influencing the tensile strength
The tensile strength of an elastomer depends on several factors:
- Polymer base: Natural rubber has very high tensile strength, Silicone or FKM are usually lower
- Degree of cross-linking: A higher degree of cross-linking increases the strength, but can reduce the elongation at break
- FillersReinforcing fillers such as carbon black or silica increase the tensile strength. Too much filler makes the material more brittle
- AgeingHeat, UV and ozone reduce the tensile strength in the long term by breaking down the polymer chains
- Hardness: Harder compounds are usually more tear-resistant but less stretchy
- Media contact: Certain media can weaken the material and reduce its strength