Quantitative fractography and dislocation interpretations of the cyclic cleavage crack growth process

Fractographic features of cyclic cleavage crack growth in Fe and Fe-binary alloys as a function of applied stress intensity and test temperature are documented. Cyclic striations, cleavage rivers and twist angle misorientations are measured and discussed in terms of geometrical and local stress considerations. It is shown that the river height displacement must account for both twist angle misorientation between adjacent grains and the crack-tip opening displacement of an advancing fatigue crack. With regards to the rate of an advancing cleavage crack, a dislocation dynamics model is derived which qualitatively gives the correct ordering of power-law slopes (da/dN vs ΔK) and growth rate magnitudes as a function of test temperature.