13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- 4.3. Results: comparisons between normal and kinked cracks Figure 8 compares the evolution of the KImax as a function of the projected crack length obtained for the two crack descriptions. Figure 8. Evolution of the KImax and R ratio as a function of the projected crack length (P=436.5 N/mm; Q=200 N/mm) computed for the two normal and kinked crack descriptions Both normal and kinked descriptions lead to similar non monotonic evolutions of the KImax values. As previously depicted in [9], the KImax value first increases with the crack length but then decreases when the tip of the crack is more and more remote from the surface due to the very sharp stress decrease induced by the severe contact stress gradients. Focusing on the comparison between kinked and the normal crack path descriptions, it can be said that in the zone 1, next to the surface, the crack angle (Θ1 = 47°) which is considered in the kinked description tends to reduce the mode I SIF value compared the normal crack description (Fig. 8. zone 1). Then, in the deeper zone 2, the angle decreases (Θ2 =15.5°) so that the KImax value extrapolated from the kinked description is becoming closer to one defined from the normal crack approximation. Finally, in the very deep region 3, the crack orientation turns to the normal direction (Θ3=0°), however the KImax value provided by the kinked description is still smaller than the value extrapolated using the normal crack description. This difference can be explained by the fact that the lateral position of the crack tip is not the same. Indeed, if the crack tip is still at the vertical of the contact border for the normal crack description, it is now located in the inner compressive part of the contact for the kinked description. A major conclusion of this comparison is the fact that the two approximations of the crack path are in fact rather close. Note that the gap between the KImax values tends to decrease in
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