PSI - Issue 24
Filippo Cianetti et al. / Procedia Structural Integrity 24 (2019) 526–540 Author name / Structural Integrity Procedia 00 (2019) 000–000
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was verified as follow. The sine on random signal was generated in time domain (Fig. 9 (a)), exactly as an input would have been generated in the laboratory to conduct the test. The PSD (Fig. 9 (b)) was derived from the time history and then superimposed on the homologous derived (17) from the levels of MIL-STD-810-H: (orange line in Fig. 9 (b)).
10 4
100
PSD from Time History PSD Expected Peak from Time History Expected Peak
Random Sine Sine on Random
80
60
10 2
40
-20 Amplitude [ms - 2] 0 20
m 2 s -4 Hz -1
10 0
10 -2
-40
-60
10 -4
-80
-100
10 0
10 1
10 2
10 3
0
0.05
0.1
0.15
0.2
0.25
time [sec]
Hz
(a) Sine time-history
(b) Equivalent PSD
Fig. 9: Validation of conversion
The peaks were compared with both methodologies verifying the consistency of the equivalence; the PSD thus calculated, weighted as required by the standard will be used in the calculation of the damage. It is known how, in the use of qualifying spectra, there is a potential over-sizing due to the time compression of the tests, in particular in fatigue and structural integrity. Having available the time histories of acceleration recorded during the flights performed to evaluate the functionality of the object, a comparison was made between the real vibratory environment and the accelerated spectrum of Fig. 9 (b). The signals were acquired during each maneuver, by means of a tri-axial accelerometer, positioned on the connection between component and helicopter. Each maneuver was analyzed isolating both pure tones, or pseudo-deterministic spectral components (Fig. 10 (a)), and the power levels of the random (Fig. 10 (b)).
X-dir Y-dir Z-dir Max
X-dir Y-dir Z-dir Max Random Levels
-1
10
-1
10
SinePeaks PR Sine Peaks TR
-2
10
-2
10
-1
Hz
-3
-2
10
-4
s
m s
2
m
-4
10
-3
10
-5
10
-4
-6
10
10
0
1
2
3
0
1
2
3
10
10
10
10
10
10
10
10
Hz
Hz
(a) Enveloped Measured PSD
(b) Exaggeration Factor
Fig. 10: MIL-STD-810-H vs Measure
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