Elongation is defined as the length at breaking point expressed as a percentage of its original length (i.e. length at rest). If a rubber reaches twice its length before breaking its elongation percentage is 100%.


To qualify an elastomer mechanically for its applied usage, it is necessary to measure the force needed to get a sample to its rupture point. Understanding the elongation for elastomers is important for determining the best option to use by our customers. Pulling a rubber sample will lead to rubber deformation. As the sample gets longer, sections will get reduced that will eventually lead to a break.


The test method determines the variability in rubber vulcanizates and the influence of parameters affecting the stress-strain properties such as temperature, relative humidity, and the preconditioning of rubber.

A traction device, called a dynometer, has an extensometer that optically or mechanically follows 2 marks on the sample. The dynometer can measure, at any time, the size of the rubber test sample during the extension pulling stage, and when the breaking point arrives.

Bone-shaped samples are stretched in the narrow section where the two marks are made. O-ring samples are often rotated during extension so that no specific zone is affected. Rotation speed is included in the results.


When gauge marks or extensometers are used to define a specific test section, only this length is used in the calculation, otherwise the distance between the grips is used as the initial gauge length.


The elongation is expressed as a percentage, and is reported out to two significant figures.

elongation percent = (elongation at rupture) x 100/(initial gauge length)

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