Issue 50

R. Boutelidja et alii, Frattura ed Integrità Strutturale, 50 (2019) 98-111; DOI: 10.3221/IGF-ESIS.50.10 105 Figure 5 : Generation of (1000 x 10 x n) times of initiation rates from 1000 values of the damage parameter, D Figure 6 : Computation of the cracks propagation rate based on fracture mechanics, for (1000 x 10 x n) generated cracks using the values of σ, a and b. Analysis of the Results The objective of this work is to study the influence of the parameters characterizing the environment modification and particularly the change in the oxygen concentration and temperature during operation. Effects of the change in the oxygen concentration For a temperature of 550 (°F), Tab. 3 resumes the steady state oxygen concentrations used to illustrate the effect of their variation. Studied case Case1 Case12 Case13 Case14 Case15 Oxygen concentration (ppm) 0.2 0.05 0.01 0.1 1 Table 3 : Studied cases Fig. 7 presents some information on the number of initiated cracks at the beginning of the time increment during the experiment (first number of cracks), and Fig. 8 presents the number of initiated cracks in the time increment (total initiated cracks: initiation and coalescence). These results are printed at each evaluation time for case1, case12, case13 and case14. For a given value of the damage D, Figs (9 to 11) show the probability of failure as a function of time. Hence besides the crack initiation probability, the probability of leak (crack crossing the wall) is evaluated for the 4 cases (1, 12, 13 and 14) respectively. For weak damages (Fig. 13) the variation of oxygen concentrations does not affect the initiation process (Fig. 12).