Drag and Limited Rate of Transport

A knee in the G(v) curves (region II) can also be due to a limited rate of transport of active species at the crack tip. When the crack velocity increases, active species present in a gas or diffusing through a liquid are less and less available at the crack tip, so that the coverage at the 

FIGURE 14. Schematic diagrams showing the effect of viscous drag due to a liquid at a crack tip. 

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