PSI - Issue 13

Daniele Rigon et al. / Procedia Structural Integrity 13 (2018) 1638–1643 D. Rigon et al./ Structural Integrity Procedia 00 (2018) 000 – 000

1641

4

The surface temperature of type (b) specimens was measured by means of a FLIR SC7600 infrared camera, operating at a sample frequency f acq equal to 100 Hz, having a 1.5 – 5.1 μm spectral response range, 50mm focal lens, a noise equivalent temperature difference (NETD) < 25 mK and an overall accuracy of 0.05 °C. The surface of the type (b) specimens was black painted in order to increase the material emissivity. The fatigue test setup is shown in Fig 3(b).

b)

a)

Fig. 3. (a) Schematic illustration of the fatigue test bench adopted for combined bending and torsional fatigue tests on type (a) specimens. (b) Test setup adopted for combined axial and torsional fatigue tests on type (b) specimens. Table 2. Fatigue tests protocol. Specimen’s geometry Loading type R    N. of tests A B -1 ∞ \ 8 T 0 \ 3 B+T 1 0 3 B+T √3 0 4 B+T 1 90 4 B+T √3 90 5 B A ∞ \ 1 T 0 \ 1 A+T √3 0 1 A+T √3 90 1 A = axial, B = bending, T = torsional. 2. Results All the fatigue test results are reported in terms of nominal net-section stress amplitude in Fig. 4. For the torsional fatigue tests, the results were plotted in terms of net-section shear stress amplitude. For type (a) specimens the shear stress has been evaluated by using Eq.(2), whereas for the type (b) specimens the shear stress was assumed uniformly distributed over the cross section and it was evaluated by means Eq.(3):

M d

16 

(2)

, t a

 = an

3

 

e

n

) ( M d d d d , t a 2 16  + en in en

(3)

 = an

(

)

2  −

in

where M t,a , d en and d in are the applied torque amplitude, the outer and inner diameters of the net-cross-section, respectively.