PSI - Issue 28

Bruno Atzori et al. / Procedia Structural Integrity 28 (2020) 1329–1339 Bruno Atzori et al./ Structural Integrity P ocedia 00 (2019) 000–000

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0 100 200 300 400 500 600 700 0.000 0.005 0.010 0.015 0.020  /2 [m/m] ep Serie6  [MPa] E=194700 MPa K'=4083 MPa n'=0.433 Cyclic stress-strain curve Filled symbols:1 st batch Open symbols: 2 nd batch  /2  E /2

Fig.3. Cyclic stress-strain curve of AISI 304L stainless steel (strain-controlled fatigue tests).

This paper refers to the second batch of material. Axial, zero-mean stress fatigue tests were carried out on specimens with the geometry reported in Rigon et al (2017) and Meneghetti et al (2016). For ease of reading, here it is recalled that samples had notch opening angle 2  =45° and 135° and notch radius equal to r n =3, 1 and 0.5 mm. The K tn values, referred to the net section are listed in Table 2 with the reference fatigue strength evaluated at 160000 cycles,  0n , and the experimental values of fatigue notch factor, K f,sper (N 0 ) =  0  0n . The experimental results are shown in Fig. 4.

500

AISI 304L R=-1

plain material, k=17.2

  = 202 MPa

Short stair-case

unbroken, broken

1

100

k

Δ  [MPa]

from Rigon et al (2017) r n =3mm, K tn = 3.41 r n =1mm, K tn = 4.85 r n =0.5mm, K tn = 6.10

10-90% P.S. scatter band from Meneghetti et al (2013): k=5.8, T  =1.30, T N =4.60

V-notch 2  =135°

from Meneghetti et al (2016) r n =3mm, K tn = 4.26 r n =1mm, K tn = 7.39 r n =0.5mm, K tn = 8.96

V-notch 2  =45°

10

1.E+3

1.E+4

1.E+5

1.E+6

1.E+7

1.E+8

N f , number of cycles to failure

Fig. 4. Fatigue data of AISI 304L plain and notched specimens (2 nd batch).

3.1. Experimental results reanalyzed according to the nominal stress approach The nominal stress approach was applied to the experimental data plotted in Fig.4 and the results are listed in Table 2. One can see that the difference between theoretical and experimental values increases as the notch tip radius