Durability and Crack Growth Testing
Introduction
Failure in rubber components is difficult to understand. The strain at failure in a tensile test can be at several hundred percent yet the parts in service can fail at strains that are only a fraction of the tensile failure. This may be because cracks that already exist or cracks that initiate and grow and cause a part fail.
Simple static tearing tests provide valuable design maximum strain and maximum stress. Fatigue of elastomers is more complex and dependent on many factors. Through a combination of testing and material related fatigue analysis, one can generate a “map” of these dependencies. Testing isn’t a matter of cycling tensile specimens under all conditions. Generating elastomeric strain-life (s-n) fatigue data sets is extremely time consuming. The use of shorter duration crack growth experiments and advanced fatigue analysis software from Endurica provides a faster and more versatile method to get important fatigue data.
Axel Products will work with Endurica to provide a general elastomer fatigue map. Axel Products will also provide individual experiments as desired.
Tear and Crack Growth Experiments:
Related Information
Elastomer Fatigue Properties Map
Fatigue of elastomers is complex and dependent on many factors. Through a combination of testing and material related fatigue analysis, one can generate a “map” of these dependencies. Testing isn’t a matter of cycling tensile specimens under all conditions. Generating elastomeric strain-life (s-n) fatigue data sets is extremely time consuming. The use of shorter duration crack growth experiments and advanced fatigue analysis software from Endurica provides a faster and more versatile method to get important fatigue data.
Comparison of observed fatigue life with Endurica-computed strain-life curves for 3 flaw sizes.
Typical images of crack tip evolution during testing.
The effect of temperature on the strength of 2 rubber compounds.
Static Tearing Energy
Failure in elastomeric parts is hard to predict and understand. Tensile failure strain data can be very misleading when materials are exposed to cuts or defects. A conservative approach to predicting failure is to use maximum strain, maximum stress and tearing energy information developed in a static tearing energy experiment. In this experiment, a cut is introduced into a planar tension test specimen and stretched until the crack grows. This experiment is often performed at multiple temperatures.
Stress Strain Loading to Crack Initiation
Planar Tension Test Specimen with a Pre-cut Crack During Loading
Dynamic Fatigue Crack Growth
The following snapshots show a few of the testing services available to those researching durability and the growth of cracks in elastomeric materials. CCD camera based vision systems have been integrated with digital servohydraulic instruments to provide crack measurements during testing. Crack images are captured at precise strain levels and at preset cyclic intervals and then processed to provide crack width and crack contour measurements along with stress and strain measurements as cyclic loading progresses.
Plot of Crack Growth vs. Tearing Energy
Planar Tension Test Specimen with a Pre-cut Crack During Dynamic Loading