13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- with the highest value of dy/dx. This is to be compared to the average dy/dx value measured as the measure peak–to–valley over half wavelength, i.e. h/l. h l a) dx dy dx dy dx dy b) c) + + + + + + Figure 9. Definition of measurements for determination of angle for crack deflection. Figure (a) represents a real interface, (b) measurement of maximum slope for theoretical sinusoidal interface and (c) measurement of average slope for theoretical sinusoidal interface. 5. Comparison of fracture-mechanical model results and microstructural damage evolution 30µm 30µm 100µm 100µm Figure 10. Typical microstructures of virgin (a) and ex-serviced materials (b) – (d). Multiple kink cracks (b) interface crack (c) and kink/white cracks after furnace testing (d). Examinations of thermally cycled material (furnace and engine exposed) reveal that the material damage is similar. To a large extent the material damage is of interface type (black) but mixed cracking (black/white kink cracks) is frequently detected. Typical microstructures are shown in Figure 10. Image (a) is as manufactured, (b) and (d) indicate mixed (kink) deflected cracks from
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