What is the tensile elongation of elastomers?

The elongation is the elongation that an elastomer specimen has reached during the tensile test at the moment of breaking, expressed in percent of the initial measurement length. Technical elastomers achieve elongation of approximately 100 to 800 %%. The English term is „elongation at break“.

How is the tensile elongation calculated?

The tensile elongation is calculated from the change in length at the moment of the tensile force and the initial measurement length of the test specimen.

In it he says L_R the measuring length when tearing in mm at and L₀ The measured length before tensile loading in mm. A tensile elongation of 100 % corresponds to a doubling of the length of the test specimen.

Computational example: A test specimen with a measured length of 20 mm in the unloaded state tears at a measurement length of 100 mm. The tear elongation is

The elongation is measured in the parallel central part of the test body, usually using an extensometer. Since the results can vary slightly, the median is given for at least three test bodies.

What tensile elongation do EPDM, NBR, FKM, silicone and other elastomers have?

Natural rubber, Polyurethane rubber and soft silicone blends achieve the highest tear strengths among elastomers, fluorocarbon rubber the lowest. The recommended values for tear strength apply to practical blends at room temperature. Since rubber blends are composed of many different components, the tear strength can vary depending on the formulation and is specified individually on the material data sheet.

What does the tensile elongation mean for the design of rubber molded parts?

The tensile elongation is a limit value from a single, short-term test on a test specimen and therefore cannot be transferred 1:1 to a rubber component and the subsequent installation situation. What is more relevant is rather how many stretch reserves the component has under the conditions of use up to this limit value.

• Mounting shrinkage: In sealing technology, the guideline for short-term expansion during assembly is to use a maximum of about 50% % of the tensile expansion.
• Local strain: On notches, sharp edges, small radii, and wall thickness splices, the local strain can be several times the nominal strain.
• Temperature and deformation: The tensile elongation decreases with increasing temperature. Molded parts with undercut sections are demolded immediately after vulcanization in a hot state, while stretching. In this state, the tensile elongation is at its lowest.
• Aging: The tensile elongation decreases over the service life due to thermal aging. The strain reserve must therefore be related to the aged state. Life-cycle assessments often use a decrease in the tensile elongation to 50 % of the initial value as a threshold criterion.

What is the difference between tensile elongation, tensile strength and tear strength?

Tensile elongation, tensile strength and tear strength are measured simultaneously in a tensile test, but describe different magnitudes. The tensile elongation indicates in percent how far an elastomer stretches until it tears. The tensile strength indicates the highest tension achieved in the test, the tear strength the tension at the moment of tearing, both in MPa.