PSI - Issue 57

Stéphan Courtin et al. / Procedia Structural Integrity 57 (2024) 4–13

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Author name / Structural Integrity Procedia 00 (2019) 000 – 000

Numerical results always provide conservative results. They are also in agreement with the level of conservatism of the four crack growth Paris laws from the French RSE-M code (2014), using the mean air law giving the highest numbers of cycles, and using the conservative PWR water environment law, the lowest ones. Thus, for a given cyclic elastic-plastic stress-strain curve , for instance the ‘shifted RCC - MRx’ option, the margins , between numerical and experimental results, on the number of cycles to reach the experimental crack length at the end of the test, are approximately in the range between 3 and 14, according to the codified fatigue crack growth law considered, the intermediate numerical results giving a margin approximately equal to 5. Accordingly with the rank of the ΔK eff values previously shown in Table 1, the ‘RCC -MRx- Sy’ option for the cyclic elastic-plastic stress-strain curve gives the highest numbers of cycles and both other options provide quite similar values, the ‘shifted RCC - MRx’ option being the most conservative. Fig. 7 shows the comparisons only with the mean PWR water environment crack growth Paris law, which is supposed to be the most representative of the experimental conditions. Here the margins, between numerical and experimental results, on the number of cycles to reach the final experimental crack length , are approximately 3 for the ‘RCC -MRx- Sy’ option and 5 for both other options. Note that applying codified plasticity correction factors of the French RSE-M code (2014), instead of considering the present ΔJ approach, using elastic-plastic calculations, leads to a higher level of conservatism. These results are not detailed here.

Fig. 7. Numerical and experimental crack growths for the so-called F3 crack with the thermal loading #1, with straight crack fronts, and with the mean PWR water environment crack growth Paris law.

5.2. Free crack fronts

Free crack fronts are now considered in the thickness of the mock-up, and two options have been taken into account for the initial crack front: a semi-elliptical one and a straight one. Note also that respectively, the ‘shifted RCC- MRx’ option, and the mean PWR water environment law, have been chosen here for the cyclic elastic-plastic stress-strain curve, and the codified crack growth Paris law. Fig. 8 illustrates the evolutions of the numerical crack fronts for both options on the initial crack front, for the so-called F4 crack (see Fig. 3). A typical semi-elliptical crack growth evolution is well obtained. Fig. 9 shows the comparisons between the numerical results and the experimental data on the bottom face of the mock-up. An influence of the shape of the initial crack front is highlighted. Here the margins, between numerical and experimental results, on the number of cycles to reach the final experimental crack length, are approximately 4.5 with the semi-elliptical initial crack front, and 2.5 with the straight one.