PSI - Issue 34

Luca Susmel et al. / Procedia Structural Integrity 34 (2021) 178–183 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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In Eqs (8) K f and K ft are the fatigue strength reduction factors under axial and torsional fatigue loading, respectively, whereas q is the notch sensitivity factor, where, by definition (Lee et al., 2005): = ℎ ( ) ℎ ( ) (9) = ℎ ( ) ℎ ( ) (10) For the AM stainless steel under consideration, q was estimated to be equal to 0.082. This value for q was calculated via the endurance limit of the uniaxial fatigue curve generated by testing the sharply V-notched specimens (K t =7.2).

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

 a,i /  a,max  a,i / a,max

1

10

100

1000

Cumulative Exceedance Cycles

Fig. 3. Adopted VA load spectrum.

The fully-reversed plain uniaxial fatigue curve had negative inverse slope equal to 15.3 and reference stress amplitude at 2 ∙ 10 6 cycles to failures equal to 249 MPa. The fully-reversed plain torsional fatigue curve was instead characterised by a slope of 32.7 and a reference shear stress amplitude at 2 ∙ 10 6 cycles to failures of 216.1 MPa. A mean stress sensitivity index, m, of 0.53 was directly determined from the plain uniaxial fatigue curve generated under R=0 (Susmel, 2009).

Sharp Notches - r n =0.07 mm

Intermediate Notches - r n =2 mm

Blunt Notches - r n =5 mm

10000000

10000000

10000000

m=0.53,  lim =1.45

m=0.53,  lim =1.45

m=0.53,  lim =1.45

Conservative

1000000 N f [Cycles]

1000000 N f [Cycles]

1000000 N f [Cycles]

Conservative r n =0.07 mm Fully-Reversed Uniaxial Scatter Band

r n =0.07 mm Fully-Reversed Uniaxial Scatter Band

Conservative

P S =5%

P S =5%

P S =5%

100000

100000

100000

10000

10000

10000

P S =95%

P S =95%

P S =95%

Ax, R=-1 Bi, IPh, R=-1 Bi, IPh, R=0 Bi, OoPh, R=-1 Bi, OoPh, R=0

Bi, IPh, R=-1 Bi, IPh, R=0 Bi, OoPh, R=-1 Bi, OoPh, R=0

Bi, IPh, R=-1 Bi, IPh, R=0 Bi, OoPh, R=-1 Bi, OoPh, R=0

1000

1000

1000

Non-Conservative

Non-Conservative

Non-Conservative

r n =0.07 mm Fully-Reversed Uniaxial Scatter Band

100

100

100

100

1000

10000 100000 1000000 10000000

100

1000

10000 100000 1000000 10000000

100

1000

10000 100000 1000000 10000000

N f,e [Cycles]

N f,e [Cycles]

N f,e [Cycles]

Fig. 4. Accuracy of the MWCM applied in terms of nominal stresses in estimating lifetime of notched AM 316 L subjected to CA loading.

The experimental, N f , vs. estimated, N f,e , lifetime diagrams reported in Figs 4 and 5 make it evident that the proposed methodology proved to be capable of estimates falling within the scatter band associated with the notch