Issue 26

A. De Iorio et alii, Frattura ed Integrità Strutturale, 26 (2013) 57-68; DOI: 10.3221/IGF-ESIS.26.07

Procedure I Adopting the procedure described in the appendix X1.2 of the ASTM E647, the crack growth rates and the corresponding ΔK values were computed (Fig. 7).

Figure 6 : Raw fatigue crack growth data.

Figure 7 : Fatigue crack propagation curve.

The crack growth rates are computed by means of local fitting of the raw data using either a second order or a third order polynomial function (Fig. 8 and 9). For each fitting n. 6 ΔK values in the neighbourhood of the references values have been chosen. A less number of points could result in a poor fitting.

ΔK (MPa  m)

da/dN (m/GC)

10

13.49 31.88 13.55 31.75

Second order polynomial function

13.5

10

Third order polynomial function

13.5

Table 3 : Crack growth rate computed using the procedure I.

Figure 8 : Second order polynomial fit of the crack growth rates.

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