PSI - Issue 39

Jesús Toribio et al. / Procedia Structural Integrity 39 (2022) 726–729 Author name / Procedia Structural Integrity 00 (2021) 000–000

727

2

The fatigue evolution of corner cracks emanating from holes has been studied by Grandt and Macha (1983), showing that the crack grows approaching a constant aspect ratio, greater with the decrease in the hole radius and the increase in the material Paris exponent (Lin and Smith, 1998; Liu and Chu, 2015). This paper studies hydrogen assisted fatigue propagation in corner cracks at holes located in tension-loaded plates. 2. Numerical procedure The material was a HSLA-80 steel, whose fatigue behaviour in air and hydrogen environments was studied by Roy et al . (2014) who obtained a Paris exponent m = 3.2 in air and m = 0.6 in hydrogen. Fatigue cracks emerge from a corner of the plate or from the edge of a hole of radius r = 2 t (Fig. 1):

w

t

a

b

w

t

a

r

b

Fig. 1. Crack emanating from the corner of a plate (left) or from a hole (right).

The stress intensity factor (SIF K ) values are those obtained by Raju and Newman (1979; 1987). The crack front was discretized and each point i shifted perpendicularly to the front following the Paris law. At point of maximum SIF K {max} the shift Δ a {max} ≡ max Δ a ( i ) is applied, while for the other points i of SIF K ( i ) the advance Δ a ( i ) is:

m

  

   

( )

K i

{ } { } max 

( ) ∆ = ∆ a i

(1)

a

max

K

Then a new crack front is obtained and the process is repeated. 3. Numerical results Figs. 2-5 show the fatigue crack growth in air and hydrogen of the two types of cracks in plates under tension. (air fatigue with Paris exponent m = 3.2 and hydrogen-assisted fatigue, i.e., corrosion-fatigue with m = 0.6). The fatigue evolution tends towards a preferential crack path ( a / b - a / t ) P . The convergence or approach between a / b - a / t curves is faster for corner cracks than in those emanating from a hole, and also quicker in air fatigue than in corrosion-fatigue. Such a convergence (or approach) is also faster for elevated values of the initial crack aspect ratio.