PSI - Issue 28

Jesús Toribio et al. / Procedia Structural Integrity 28 (2020) 2390–2395 Jesús Toribio et al. / Procedia Structural Integrity 00 (2020) 000–000

2393

4

Fig. 2. Fracture surfaces and their respective schemes for different types of MFM: (a) type I; (b) type II; (c) type III; (d) type IV.

4. Discussion Table 1 shows the different micromechanical models of hydrogen-assisted micro-damage depending on notch type, drawing degree and crosshead speed. From data included in this table the following trend is revealed (Fig. 3): as drawing degree is increased the MFM evolves from type I –semi-elliptical TTS region– to type III –ring-shaped TTS zone–, cf. Toribio and Vergara (2013). However, notch type D exhibits a different behaviour when the slow speed is applied (0.001 mm/min), and the MFM type IV appears instead MFM type III. Table 1 summarizes the type of MFM as a function of the degree of cold drawing in the material, the stress triaxiality (constraint) given by the notch geometry and the crosshead speed applied on the notched sample. Table 1. Type of MFM as a function of the degree of cold drawing, the stress triaxiality (constraint) and the crosshead speed.

Notch A

Notch B

Notch C

Notch D

Cold Drawing Steps

Speed 2 Speed 1 Speed 2 Speed 1 Speed 2

Speed 1 Speed 2

Speed 1

0

I

I

II

II

I

I

I

I

1

I

I

II

II

II

II

II

II

2

I

I

II

II

II

II

IV

II

3

II

II

II

II

II

II

IV

III

4

II

II

II

II

II

II

IV

III

5

II

II

III

III

II

II

IV

III

6

II

II

III

III

II

II

IV

III