PSI - Issue 19

P. Cussac et al. / Procedia Structural Integrity 19 (2019) 463–471 P. Cussac / Structural Integrity Procedia 00 (2019) 000 – 000

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D = 9mm

a

b

Fig. 4. Semi-elliptical crack front characterized by the ratio a/b

During the propagation, the crack front retains a semi-elliptical shape, first evolving towards a circular shape before stabilizing around a shape having an ellipticity ratio a/b close to 0.7. The propagation history (Fig. 5a) is relatively close to the evolution of the crack front modeled by Carpinteri [Carpinteri (1993)] under similar conditions (initial notch: a/D = 0.05 and a/b = 0.25). However, we demonstrate here that there is no influence of the initial depth of imperfection in the present results, whereas Carpinteri has highlighted a difference in the evolution of the crack front, in the early stages of propagation, depending on the geometry of the initial notch. He has also shown that, independently of the initial imperfection shape, the crack front shapes always converge towards the same semi-elliptic shape with a ratio a/b close to 0.7, which is consistent with the results presented in Fig. 5.

Fig. 5. Evolution of the crack front shape (characterized by the ratio a/b) as a function of the normalized crack depth a/D

The analysis of the final crack fronts (after complete failure of the specimens) and the ink markings on the fracture surfaces (Fig. 5b), in correlation with the measurements of the electrical potential also allowed to build an experimental calibration curve. The curve shown in Fig. 6 collects the markings made on several fatigue tests, without