PSI - Issue 41

Jesús Toribio et al. / Procedia Structural Integrity 41 (2022) 728–735 Jesús Toribio / Procedia Structural Integrity 00 (2022) 000–000

734

7

To assess the model proposed in this paper, a comparison was made with a previous kinematic model for notched samples on the basis of a numerical method. To this end, Fig. 5, taken from paper by Toribio and Elices (1992) and plotted in the same scale as Fig. 4 gives the dimensionless results of HAC tests performed on notched samples of very similar pearlitic steel under exactly the same environmental conditions.

Fig. 5. Results of the SSRT under HAC conditions performed on notched samples,: ftacture stress as a function of the CTSR.

Different notched geometries (A, B, C, D) were used with very distinct triaxiality (constraint) levels to provide unlike hydrostatic stress distributions in the vicinity of the notch tip and therefore different rates of hydrogen transport by stress-assited diffusion. Horizontal dashed lines correspond to the quasi-static tests, which limit the applicability range of the kinematic formulation. It can be observed that both sets of experimental results show the same trend when expressed in terms of the dimensionless local strain rate in the vicinity of the crack or notch tip, which confirms the very important role of this variable in hydrogen embrittlement processes in the presence of stress or strain localization near a crack or notch tip. Furthermore, on performing a linear fitting on the results of Fig. 4 (cracked samples) and Fig. 5 (notched samples), the following equations are obtained: C RACKED SAMPLES :  * = 0.13 log  * + 0.96 (  * ≥  * ∞  ) N OTCHED SAMPLES :  * = 0.15 log  * + 0.99 (  * ≥  * ∞  ) which demonstrates that the two approaches produce an almost identical kinematic relationship between the dimensionless stress  * and the dimensionless strain  * (the latter representing the CTSR or the NTSR). These equations are only valid above the asymptotic values of the dimensionless stress and strain (  ∞ *and  ∞ *) associated with the quasi-static tests in which there is no kinematic effect. These asymptotic values are influenced by the level of stress triaxiality (constraint) in the specimens, so the minimum is achieved in precracked samples and it increases as the triaxiality factor of the geometry decreases.