Issue 35

S. Blasón et alii, Frattura ed Integrità Strutturale, 35 (2016) 187-195; DOI: 10.3221/IGF-ESIS.35.22 193 b- Minimization of function Q Thereafter, the parameters fitting the crack growth rate curve are determined from the experimental data (see Tab. 4). α γ log(ΔK th * ) log(ΔK up * ) -3.7462 1.9224 -1.7159 0.5721 Table 4: Parameter values found by fitting the crack growth rate curve as a cumulative distribution function. Fig. 6 exhibits the normalized values for log(ΔK*) vs. log(da*/dN*) along with the curve fitting obtained after minimization. Figure 6: Representation of the normalized experimental data and fitting obtained. c- Obtaining crack growth curves Figs. 7 and 8 represent the result of the integration of Expr. (4), firstly for different initial crack sizes a 0 * when maintaining a fixed value for the non-dimensional stress range, Δσ*. Figure 7: Curves a*-N* for different initial crack sizes a 0 *, while maintaining constant Δσ*. Figure 8: a*-N* curves for different stress ranges, Δσ*, while maintaining the initial crack size, a 0 * constant The integration follows after fitting the geometric factor to the first Expression in (6). Fig. 9 illustrates the fit obtained for the geometrical crack factor in the specimen 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 -16 -14 -12 -10 -8 -6 -4 -2 0 2 g log(  K*) log(da*/dN*) 0 100 200 300 400 500 600 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9  0 =141[MPa] normalized number of cycles, N* normalized crack length, a* a 0 =3.4 mm a 0 =3.6 mm a 0 =4.0 mm a 0 =4.5 mm 0 50 100 150 200 250 300 350 400 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 normalized number of cycles, N* normalized crack length, a* a 0 =3.4 [mm]  =136 MPa  =146 MPa  =171 MPa  =196 MPa