PSI - Issue 24

Filippo Cianetti et al. / Procedia Structural Integrity 24 (2019) 526–540 Author name / Structural Integrity Procedia 00 (2019) 000–000

537

12

can be associated with the number of cycles in the unit of time. Being a broadband process, the distribution of the amplitudes of the cycles is well described by the probability density function (pdf) of Dirlik (Fig. 12 (b)), which combines two Rayleigh and one exponential distributions allowing an accurate estimate of the range of cycles to large and small amplitudes Dirlik (1985). After defining the distribution of the amplitudes of the cycles, the calculation of the damage was carried out with the Palmgren-Miner rule, as suggested by the MIL-STD-810-H standard Fatemi and Yang (1998):

n i = 1

n i N i

D =

(25)

0.02

25

2

[m/s

]

0.01

- 3

20

0

-0.01

15

-0.02

-0.03

10

Stress [MPa]

-0.04

-0.05

5

-0.06

-0.07

0

0

5

10

15

20

25

30

35

40

0

0.5

1

1.5

2

2.5

3

3.5

10 -7

time [sec]

Occurrency

(a)

(b)

Fig. 12: (a) Signal Statistical Properties, (b) Dirlik Distribution for one element

3.2. The Damage Maps

The described procedure has generated a virtual test that was interrupted when the unitary damage in at least one point (i.e. a small group elements) of the component was reached; the duration of the test, as described in Par. 2.4, leads to an estimate of 1000 flight hours. Fig. 13 shows damage maps on a base 10 log scale.

(a) Overview

(b) Detail

Fig. 13: Final PSD & Exaggeration Factor

As was to be expected, the damage reaches critical values in the stress concentration zones.