PSI - Issue 28

Jesús Toribio et al. / Procedia Structural Integrity 28 (2020) 2444–2449 Jesús Toribio et al. / Procedia Structural Integrity 00 (2020) 000–000

2448

5

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

F/F max

F/F max

0.1 0.8 0.7 0.9 0.6 0.4 0.2 0.3 0.5

0.1 0.8 0.7 0.9 0.6 0.4 0.2 0.3 0.5

c/c 0

c/c 0

x

x

R/D=0.04 C/D=0.3

R/D=0.04 C/D=0.1

0

1

2

3

4

5

0

1 2

3

4

5

x (mm)

x (mm)

(a) (b) Fig. 4. Concentration of hydrogen c / c o in the minimum section of sharply notched specimens : (a) C/D = 0.1 ( shallow sharp notch ); (b) C/D = 0.3 ( deep sharp notch ).

2.0

5.0

C/D=0.1 C/D=0.2 C/D=0.3 C/D=0.4

4.0

R/D=0.04

1.5

3.0

1.0

R/D=0.04

c  /c 0

2.0

x S (mm)

0.0 0.2 0.4 0.6 0.8 1.0 C/D=0.1 C/D=0.2 C/D=0.3 C/D=0.4

0.5

1.0

0.0

0.0

0.0 0.2 0.4 0.6 0.8 1.0

F/F max

F/F max

(a) (b) Fig. 5. Hydrogen concentration at the boundary ( notch tip ) c Г / c o vs load ratio F / F max . (a) and depth x S of the maximum hydrostatic stress point (b). Toribio et al. (1991) demonstrated that the hydrostatic stress is the macroscopic variable governing the microscopic fracture of pearlitic steels in hydrogen, i.e., governing mainly the hydrogen penetration at the inner boundary of the notched specimens and further transport towards the inner points of the specimens by a mechanism of transport by stress-assisted diffusion of hydrogen (Toribio 1992, 1993, 1996). Considering these evidences, the position of the maximum hydrostatic stress point towards which hydrogen mainly diffuses is of the highest interest in hydrogen embrittlement analyses. It is the point of maximum hydrogen concentration in the steady state regime , Fig. 5b shows the numerical results regarding the calculation of the maximum hydrostatic stress point depth x S as an increasing function of the of the load ratio F / F max and of the notch depth. This important length has a relevant fractographic meaning, since it coincides with the asymptotic depth ( for quasi-static tests or steady state regime ) of the TTS zone or hydrogen-assisted micro-damage area in pearlitic steels, as reported by Toribio et al. (1991), Toribio and Vasseur (1997) Toribio (1997), Toribio (2012) and Toribio (2018).