PSI - Issue 57

Marco Bonato et al. / Procedia Structural Integrity 57 (2024) 799–809 / Structural Integrity Procedia 00 (2019) 000 – 000

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In the case of SpR, the two signals are consecutive, therefore the FDS of the Random part can be added to the FDS of the shock part and the total cumulative FDS obtained. The FDS of the shock pulses is obtained from the time series of the half sine; the FDS of the PSD is calculated via the Lalanne spectral method (Lalanne (2002)). The reverse of the sum of the two FDS allows to create the damage equivalent PSD or sine sweep, for the above-mentioned combination of b and Q, depending on the targeted failure mode. For the case study here considered, the equivalent PSD has the same duration of the original PSD. The B asquin’s exponent and damping ratio parameters are considered to capture both the mechanical and electronic failure. The graph below represents that b8Q10 is more severe compared to the other combinations b4Q25 and b8Q25. The equivalent random signals generated are tested in the HVCH model using nCode to predict the life.

Fig 4. Sensitivity of b & Q factor for a equivalent random spectrum

2.3.

Sine-on-Random for Alternator The harmonic and random parts of the test requested for the alternator are shown in figure 4.

The 30-hours signals come from an accelerated vibration specification as proposed by one of our customers. This has a typical level of severity commonly applied in the automotive industry as generic validation tests for components mounted on the engine. The signals have the harmonic part superimposed on the random part, which is transient in nature, therefore the FDS of each signal cannot be added one to the other, nor calculated directed via spectral methods. One needs to generate the time series of the signals, with a sufficient number of points for a statistical representative FDS generation. The rule of thumb is 1 million points. Because the maximum frequency is 1980 Hz, the time series had a duration of 458 seconds for one sweep and a sampling period of 10 000 Hz.

Fig. 5. (a) Sine signal in frequency domain (b) Random vibration in frequency domain