13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- Figure 3. Crack path description a) Schematic and photo of the 2196-UA at N=2.106 - b) Discretization of the real crack path This typical crack path evolution will be considered later for the crack modelling. To simplify the crack length analysis only the projected crack length (bp parameter on Fig. 3) was considered. Figure 4 compares the evolution of the maximum projected crack length which was represented as a function of the fretting cycle. Figure 4. Propagation's curves For the two materials, asymptotic evolutions can be observed. This analysis shows that the maximum crack length stabilized after 106 cycles. This allows us to estimate the crack length related to the crack arrest condition for the studied (P=436.5 N/mm; Q*=200 N/mm) plain fretting condition. We found respectively for the T8 and UA ageing treatments the following bpth(T8)=280 µm and bpth(UA)=100 µm crack length values. Because the maximum crack length achieved for the T8-ageing is longer than the one observed for the UA-ageing, it can be intuited that the threshold Stress Intensity Factor (SIF) related to the T8-treatment is significantly smaller than the one expected for the UA-ageing. The following analysis will consist in quantifying this aspect.
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