PSI - Issue 33

Jesús Toribio / Porcedia Structural Integrity 00 (2021) 000–000

3

Jesús Toribio et al. / Procedia Structural Integrity 33 (2021) 1215–1218

1217

1000 1200

0 200 400 600 800

σ (MPa)

0.00 0.02 0.04 0.06 0.08

ε

Fig. 2. Characteristic stress-strain curve σ - ε of pearlitic steel (standard tension test).

100

80

60

R/D=0.40

40

0 0.0 0.5 1.0 1.5 2.0 2.5 C/D=0.1 C/D=0.2 C/D=0.3 C/D=0.4

F (kN)

20

u (mm)

Fig. 3. Load-displacement curves F - u for specimens with blunt notches of different depths.

4. Chemical analysis Hydrogen transport by stress-assisted diffusion was used in this paper (Van Leeuwen, 1974), according to which hydrogen diffusion is driven by the gradient of hydrostatic stress as follows:

σ = Δ − ∇ ∇ − Δ ∂ c D c M c Mc t ∂

(1)

σ

where c is the concentration of hydrogen in the steel, t the time, D the hydrogen diffusion, σ the hydrostatic stress and M a second coefficient (M = D V H /RT, V H being the partial molar volume of hydrogen in the metal, R the ideal gas constant and T the absolute temperature. The boundary condition is a Boltzmann distribution as follows:

V

σ ⎛

⎞ ⎟ ⎠

c c =

0 exp

,

(3)

H

⎜ ⎝

r

RT

where c 0 is the equilibrium hydrogen concentration in the metal in the absence of any stresses. This equation is also the stationary solution of the diffusion problem.