Dislocation dynamics of crack-tip processes-Frequency observations and theoretical modeling

The general features of static and dynamic models of fatigue crack propagation are briefly reviewed. It is concluded that to sort out the relative applicability of static versus dynamic models that planar crack fronts moving on cleavage planes might be most informative. Specifically, the frequency dependence of fatigue crack growth rate was selected as the important observation. Experimental data for both Fe-based polycrystals and single crystals are presented with emphasis on the latter. It is shown that a two decade decrease in test frequency may result in a factor of three increase in crack velocity on single crystal {001} planes oriented for macroscopic 〈010〉 growth. Further analysis, similar to group dislocation models proposed by Yokobori and colleagues, demonstrated that such frequency observations may be interpreted in terms of the dislocation velocities associated with a crack-tip field.