PSI - Issue 39

Giovanni Pio Pucillo et al. / Procedia Structural Integrity 39 (2022) 700–710 Author name / Structural Integrity Procedia 00 (2019) 000–000

704

5

Two maximum nominal load levels, σ max , were chosen for fatigue tests, 290 and 400 MPa, with a loading ratio R = σ min / σ max equal to 0.05.

a)

b)

Measuring range: 4.6 mm Grid interval: 0.1 mm

Measuring range: 20 mm Grid interval: 0.5 mm

Fig. 3 – Crack gauges glued for the experiments.

2.2. Results The effects of cold expansion on the fatigue crack growth are presented in this sub-section. Data acquired by crack gages for both load levels, namely 400 MPa and 290 MPa, are reported in Fig. 4. As you can see, for cold expansion degree equal to 2% the fatigue life increases of about 50% to 100%, whereas with 4% of CE an increase of about 200% is found. This is a very important result in the railway sector, in particular for the extension of the fatigue life of rail end bolt hole, which is not present in the current literature.

20

20

a)

b)

15

15

Not Expanded Expanded @ 2% Expanded @ 4%

10

10

a [mm]

a [mm]

5

5

0

0

0

0,5

1

1,5

2

2,5

0

0,01 0,02 0,03 0,04 0,05

N [cycles]

x 10 6

x 10 6

N [cycles]

Fig. 4. Fatigue crack growth data. Maximum load equal to 290 MPa (a) and 400 MPa (b).