Q2. How much hydrogen coverage is attainable in the low trap density model?
For the low trap density model, the maximum attainable trapped concentration of 0.033 wppm corresponds to a hydrogen coverage of 0.29 and a reduction in cohesive strength of 29 %.
Q3. What is the importance of assessing the hydrogen distribution in the material?
In order to predict the degrading effect of hydrogen on the mechanical properties, it is of fundamental importance to correctly assess the hydrogen distribution in the material.
Q4. What is the common method of implementing hydrogen influence into the cohesive model?
Most known attempts of implementing hydrogen influence into the cohesive model is through the HEDE principle [11, 15, 16, 58, 59, 60]; hydrogen reduction of the cohesive energy at fracture.
Q5. How much is the effective diffusivity ratio at the notch tip?
Assuming EB = 60 kJ/mol, the effective diffusivity ratio at the notch tip yield 0.62 and 0.005 for the low and high trap density models, respectively, at an initial concentration of 0.00034 wppm.
Q6. How can the authors determine the binding energies of trap sites?
Trap sites and trap binding energies can be established experimentally for a microstructure using varies approaches like electrochemical permeation or thermal desorption spectroscopy (TDS), with TDS considered best suited to provide detailed trap characteristics [5, 13, 23].
Q7. How many times an initial lattice concentration is 0.00034 wppm?
For the high trap density model, the maximum attainable trapped concentration is 10.1 wppm, 30000 times an initial lattice concentration of 0.00034 wppm.
Q8. How is the dislocation trapped hydrogen concentration calculated?
Using Equation (1) - (5), the dislocation trapped hydrogen concentration, CT , is calculated as a function of the lattice hydrogen concentration, CL, in terms of the trapping models by Kumnick and Johnson [2] and Sofronis et al. [34, 35], assuming VM = 7.106 · 10−6 m3/mol, β = 6, α = 1 and room temperature.
Q9. How can the authors estimate the hydrogen dependent cohesive stress for the fast separation case?
Using parameters representing of Fe (110); (2γint)0 = 4.86 J/m 2 and Γmax = 5.85 · 10−5 mol/m2 [55], assuming ∆g0i −∆g0s = 74.5 kJ/mol [13], the hydrogen dependent cohesive stress for the fast separation case can be estimated.
Q10. Why is austenite more diffusive than ferrite?
The substantially higher diffusivity in ferrite compared to austenite is due to the lower packing density of bcc metals, reducing the potential energy barrier for jumps.
Q11. What is the effect of the trap density on the effective diffusivity?
when the lattice concentration is increased from 0.00034 wppm to 1 wppm, maintaining a constant trap binding energy level, the effective diffusivity will increase.
Q12. What is the cleavage energy of Al(111) and Fe(110)?
An almost linear decrease in cleavage energy with increasing hydrogen coverage is observed for both Al(111) and Fe(110), as displayed in Figure 8b.