Excitation mechanisms with a high level of randomness (e.g. shaker excitation on test benches or road excitation) lead to an increase in calculation effort due to the long time series that become necessary. FEMFAT spectral offers an ideal solution for this. The multiaxial damage analysis is carried out directly in the frequency domain (“Random Response Fatigue”), which dramatically reduces the duration of the fatigue calculation.
To do so, SPECTRAL uses the alternative description of signals in the frequency domain, so-called PSDs – Power Spectral Densities. The multiaxial damage analysis is carried out in the frequency domain.
Similar to a channel-based simulation with ChannelMAX, FEMFAT spectral employs a unit-load-based approach. This considers a unit excitation that is constant over the frequency for each individual load direction. An efficient numerical simulation of these loads is made possible by using a modal frequency response analysis in the frequency domain. The results obtained are the corresponding modal stresses and a set of modal transfer functions per unit load case. From this, SPECTRAL generates the corresponding transfer functions of the local stresses which are then scaled with the power densities of the loads resulting in the overall load which is actually applied.
Due to the fact that in many applications, the loads are not applied completely independently of each other, FEMFAT spectral offers the option of considering phase relationships between the individual loads by defining cross power spectral densities (cross PSDs). The use of cross PSDs offers the additional advantage that the formation of the equivalent stress PSDs can be carried out in a manner that is statistically correct.
For the subsequent damage analysis, in addition to the classical cutting-plane method, probability models according to Dirlik or Rayleigh are used.