Why Cutting Strength is an Indicator of Fatigue Threshold

Crack tip fields during cutting and tensile loading have been computed via finite element analysis, and measured using Digital Image Correlation during experiments executed on the Coesfeld Intrinsic Strength Analyser. The results show that cutting with a sharp blade while the specimen is under a small amount of tension produces a much-reduced dissipative process zone in front of the crack tip, in comparison with the process zone produced by tensile loading alone at nominally similar conditions. Because the energy released by a growing crack supplies both the process of breaking polymer chains to form crack faces, and the dissipative process at the crack tip, minimizing crack tip dissipation causes the observed remaining energy release rate during a cutting experiment to approach the limit reflecting the breakage of polymer chains. Conveniently, this implies that a relatively brief cutting experiment may be used as an indicator of long-term fatigue behavior.