13th International Conference on Fracture June 16–21, 2013,Beijing, China -7- Kmax and ∆K [24] as follow: ࡷ∗ ൌሺࡷࢇ࢞ሻࢻሺ∆ࡷሻି ࢻ (3) Where ∆K is the positive part of the range of the applied stress intensity factor. This parameter is characterized, among other things, by the use of two separate variables that could describe unambiguously the load cycle at least if the load ratio is positive and Kmax is greater than 0, like in the present case. The α value is a factor that determines the importance of Kmax or ∆K and it is calculated by means of the following expression: ࢻൌ ࢍሺ∆ࡷ/∆ࡷሻ ࢍሺሺെࡾሻ/ሺെࡾሻሻ (4) Figure 7. Fatigue crack growth rate as a function of the Kujawski`s parameter with α equal to 0.6. Using Eq. (4) the average α value, for the AISI 301 LN in the paris region, was equal to 0.6. This was the same α value found for the metastable austenitic stainless steel AISI 304L tested at 77K [8], although in that case the scatter was higher. Fig. 7 shows the correlation obtained by plotting the fatigue crack growth rate vs the Kujawski`s parameter far from the threshold region. It is seen that kujawski`s parameter can unify the curves of the test performed to constant load ratio into a master curve that can be described by using Eq (5) with C = 1.33×10-11 [mm/cycle MPa m0.5m] and m = 3.619. ࢊ ࢊ ࡺ ࢇ ൌሺ∆ࡷି ࢻࡷࢻ ࢇ࢞ሻ (5) (a) (b)
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