PSI - Issue 57

402 Pierrick Lepitre et al. / Procedia Structural Integrity 57 (2024) 395–403 Author name / Structural Integrity Procedia 00 (2019) 000 – 000 ( ( = −1) ( ) ) = ( ) ( = −1) . (8) Self-heating model parameters and estimated fatigue properties are summed up in Table 3. As no conventional fatigue results are available for R = -0.25, fatigue limit is interpolated linearly between characterized values at R = -1 and R = 0.1 (using the Goodman relation). This leads to a value of σ D = 705 MPa, very close to the self-heating estimation ( σ AE = 710 MPa). 8

Table 3 – Self-heating model parameters and estimated fatigue limit for 300M bare steel at R = -0.25 Parameters Unity R = -0.25 Σ 0 MPa 1 000 α µJ.mm -3 .cycle -1 2.87 p - 2.1 β µJ.mm -3 .cycle -1 417 m - 28 σ AE MPa 710

Figure 5 - Self-heating curve of 300M steel in a log-log diagram, for R = -1 and -0.25, with the identified self-heating model

4. Conclusion In this paper, the self-heating test protocol, the stabilized temperature post processing and the (Munier) self -heating model have been implemented and validated for the ultra-high tensile strength steel 300M. On six test coupons, the repeatability of the self-heating curve has been validated as every coupon shows the same dissipation. At a loading frequency higher than 100 Hz, the thermal signal is excellent, even for very low loading amplitudes. The model describes well the 300M temperature rise evolution (saturating exponential and exponential decay). Moreover, no volume effect on the self-heating curve is observed between 800 mm 3 and 375 mm 3 ,indicating that testing volumes are larger than the dissipated representative elementary volume. At R = -1, the 300M self-heating curve is very well described by the self-heating model. The two dissipation regimes are easily noticeable. By identifying the self-heating model and choosing a threshold of 1 %, the mean fatigue limit has been estimated by self-heating tests at σ AE = 895 MPa. The self-heating model also gives the estimated