Elongation at break
#1 What is elongation at break?
The elongation at break reflects the ability of materials to deform.
In the case of O-rings, the elongation at break is determined by means of the world-famous tensile test using a material sample. The sample is clamped in a machine and stretched until it tears. The extent to which the sample could be stretched is then tested.
The elongation at break is given as a percentage on each data sheet.
Example: If an O-ring material has an elongation at break of 100%, then the material could be stretched to twice its length.
#2 Which O-ring material has which elongation at break?
Material | Hardness | Elongation at break | Tear resistance |
|---|---|---|---|
FFKM | 75 Shore A | 145% | 18.0 MPa |
FKM (Viton) | 75 Shore A | 183% | 14.9 MPa |
FEP/FKM | 90 Shore A | 250% | 21.4 MPa |
PTFE | 60 Shore D | 250% | 24.5 MPa |
Silicone | 70 Shore A | 261% | 6.1 MPa |
HNBR | 70 Shore A | 274% | 18.0 MPa |
EPDM | 70 Shore A | 282% | 10.9 MPa |
FVMQ | 70 Shore A | 285% | 7.6 MPa |
NBR | 70 Shore A | 389% | 14.4 MPa |
The mechanical load capacity of the O-ring material can be easily read from the table.
Analysis of the table
In general, it can be said that a high elongation at break results in a low tensile strength (e.g. VMQ (silicone) or FVMQ). Against this background, NBR and HNBR stand out in particular.
HNBR and NBR O-rings have both a very high elongation at break and excellent tear resistance. This is also the reason why NBR or HNBR O-rings are used when there is a high mechanical load.
Note: The FEP/FKM and PTFE O-rings must be considered separately in this table, as they are not elastomers like the other materials. FEP encapsulated O-rings are a combination product made of thermoplastic (FEP encapsulation) and elastomer (FKM core). PTFE is a duromere.
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