PSI - Issue 26

Sabrina Vantadori et al. / Procedia Structural Integrity 26 (2020) 106–112 Vantadori et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 1. Electric servo-controlled multiaxial fatigue testing machine (Ref. by Morishita et al., 2016).

The fatigue life is experimentally defined as the number of loading cycles needed to reduce the maximum inner pressure, which is due to an oil leak resulting from the initiation and propagation of a through-the-thickness crack or failure of the specimen. Therefore, under both cyclic axial loading ( R =0) and push-pull loading ( R =-1), a constant inner pressure of 1MPa was applied during testing to ensure a standard definition of fatigue life N exp .

Table 3. Stainless steel 316: stress state in the inner surface of each specimen examined. TEST TYPE TEST NO. , r a  [MPa] , r m  [MPa] , a   [MPa] , m   [MPa] , z a  [MPa]



, z m 

exp N [cycles] 122000 159600 118000 201800

[°]

[MPa] 256.05 227.57 256.35 240.00

T1 T2 T3 T4 T5 T6 T7 T8 T9

0.50 0.46 0.50 0.50

- - - -

3.27 3.01 3.27 3.27

- - - -

256.05 227.57 256.35 240.00

180 180 180 180 180 180 180 180 180 180 180 180

AXIAL LOADING

32.67 36.15 33.85

-32.67 -36.15 -33.85

213.61 236.37 221.33

213.61 236.37 221.33

- - -

- - - - - - -

29300 26300 29700

INNER PRESSURE

0.47 1.00 1.00 1.00

- - - -

3.07 6.54 6.54 6.54

- - - -

442.90 512.70 480.00 443.20 200.20

785 208 680 788

PUSH-PULL

T10 T11 T12

36.15

-36.15

236.37

236.37

200.20

24700

AX. LOADING + INNER PRESSURE

T13

33.85

-33.85

221.33

221.33

187.50

187.50

180

25850