13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- depth. Beside the normal approximation leads systematically higher KImax values providing conservative descriptions of the crack propagation's risk. Confirming former analytical analyses [9], it can be concluded that the usual "normal" crack path description provides relevant and conservative estimations of the fretting KImax evolutions. This result is important because it supports numerous plain fretting and fretting fatigue crack propagation's descriptions given in the literature. 4.4. Identification of the ΔKth crack arrest value By reporting the maximum projected crack length bpth(T8) and bpth(UA) on the previous graph, it is possible to extrapolate the related ΔKIth crack arrest value. Hence assuming the "Normal" crack's description we found: K T MPa m Ith N . ( 8) 1.6 _ = Δ (R=-0.9) and K UA MPa m Ith N . ( ) 2.7 _ = Δ (R=-0.9) Whereas using the "kinked" crack description we obtain: K T MPa m Ith K . ( 8) 1.2 _ = Δ (R=-0.9) and K UA MPa m Ith K . ( ) 2.6 _ = Δ (R=-0.75) The extrapolated values are rather small but quite representative of values for such aluminium alloys. Note that such values come from very low stress ratios (R) conditions, which is quite uncommon in conventional fatigue investigations. Considering the "Normal" crack description, which is usually the case in the literature for fretting fatigue cracking's characterizations, we can compare the obtained values with the ultimate stress values (Fig. 9.). Figure 9. The ultimate stress as a function of ΔKth We confirm that for a given alloy, a heat treatment inducing an increase of the ultimate stress, leads to a decrease of the ΔKIth. Further developments will consist in comparing the ΔKIth identified from this inverse fretting identification's approach with conventional crack propagation fatigue analysis, thus to evaluate the pertinence of this approach and to estimate how very low stress R ratios can be considered regarding the crack arrest process. Besides, mixed mode descriptions including the mode II contribution and the friction coefficient in the crack lips will be addressed. 5. Conclusion Using this reverse analysis, the ΔKIth values related to two different microstructures of a similar
RkJQdWJsaXNoZXIy MjM0NDE=