PSI - Issue 41

R. Nobile et al. / Procedia Structural Integrity 41 (2022) 421–429 Riccardo Nobile et al. / Structural Integrity Procedia 00 (2019) 000 – 000

428

8

Table 3. Percentage variation of ΔR/R 0 at approximately 20-40% of fatigue life for AISI 316L.

Percentage variation of (ΔR exp /R 0 ) [%]

Percentage variation of (ΔR damage /R 0 ) [%]

Stress amplitude [MPa]

Specimen

P1 P2 P3 P4

416.39 366.54 333.11 266.67

3.62 4.04 6.00 8.36

3.14 3.59 7.00 8.13

Figure 10 shows an example of cross-sections observed with the stereo microscope (model Nikon SMZ 1000) with clearly visible cracks location highlighted in white after fatigue failure of each specimens tested.

cracks

(c)

(a)

(b) (d) Fig. 10. Example of fatigue fracture surface with visible cracks observed with the stereo microscope of a stainless steel AISI 316L for the specimens P 1 (a), P 2 (b), P 3 (c), and P 4 (d).

4. Conclusions In the present work the Electrical Resistance method was conducted for the application of the method on austenitic AISI 316L stainless steel specimens to monitor fatigue damage in-situ and in real-time. From the results, it was observed that resistance decreases in the initial stages of loading and subsequently, starting from about 20-40% of the fatigue life, shows a rapid increase associated to an irreversible fatigue damage of the material. The sudden increase in electrical resistance is inversely proportional to the applied load. This behaviour could be explained assuming that the larger size of the plastic area at the notch tip determines a smaller quantity of