Characterising the cyclic fatigue and static tear resistance of HNBR compounds

HNBR is commonly used in elastomer components that undergo severe mechanical loading under harsh thermal and chemical environments. Elastomer applications for oil and gas often feature high strains, high strain rates, wide temperature ranges, contact with organic solvents as well as high pressures. As a consequence of its acrylonitrile content and its high level of hydrogenation, HNBR is suitable for many oil and gas sealing applications. However, it is not always clear how HNBR compounds respond under these extreme conditions, where it often performs above expectation. Of particular interest is the origin of its high levels of mechanical toughness. This paper aims to further understand this behaviour by characterising a typical oil and gas elastomer at high temperatures under a range of different ageing conditions. A fracture mechanics-based fatigue study where cyclic fatigue test results are contrasted with the tear resistance results from trouser tear tests. These are undertaken on typical HNBR engineering compounds with different levels of carbon black filler to explore their tear and fatigue resistance at different conditions including temperature and ageing. Results indicate a surprisingly complex cyclic fatigue and static tear behaviour for these materials. Results can often feature experimental scatter due to significant transitioning regions between smooth and knotty tearing. Ageing and testing at elevated temperatures appear to encourage knotty tearing behaviour and ageing can on occasion be seen to help develop even tougher materials. DSC and X-Ray diffraction tests are used to explore the potential mechanisms behind this behaviour
HNBR is commonly used in elastomer components that undergo severe mechanical loading under harsh thermal and chemical environments. Elastomer applications for oil and gas often feature high strains, high strain rates, wide temperature ranges, contact with organic solvents as well as high pressures. As a consequence of its acrylonitrile content and its high level of hydrogenation, HNBR is suitable for many oil and gas sealing applications. However, it is not always clear how HNBR compounds respond under these extreme conditions, where it often performs above expectation. Of particular interest is the origin of its high levels of mechanical toughness. This paper aims to further understand this behaviour by characterising a typical oil and gas elastomer at high temperatures under a range of different ageing conditions. A fracture mechanics-based fatigue study where cyclic fatigue test results are contrasted with the tear resistance results from trouser tear tests. These are undertaken on typical HNBR engineering compounds with different levels of carbon black filler to explore their tear and fatigue resistance at different conditions including temperature and ageing. Results indicate a surprisingly complex cyclic fatigue and static tear behaviour for these materials. Results can often feature experimental scatter due to significant transitioning regions between smooth and knotty tearing. Ageing and testing at elevated temperatures appear to encourage knotty tearing behaviour and ageing can on occasion be seen to help develop even tougher materials. DSC and X-Ray diffraction tests are used to explore the potential mechanisms behind this behaviour