In recent years API 579 has provided the analyst with a detailed outline of the Wang-Brown algorithm (WB) for the cycle counting. The WB algorithm has become the generally accepted core of cycle counting implementations whenever multi-axial non-proportional fatigue stress histories are encountered. However, for vibration based fatigue, in the absence of any time history at all; it is common in industry to assess fatigue using frequency domain techniques. In the frequency domain the stress cycles are counted a priori. However the stress amplitudes are not immediately accessible from the complex stress tensor.

In this paper, the determination of the spectral stress amplitudes is considered for a fatigue assessment in the spirit of API 579. To this end, steps will be outlined that that need to be taken in order to sufficiently accurately maintain the stress tensor component phase relationships. The modified Wang-Brown algorithm (MWB) proposed by Meggiolaro et al makes use of a sub-space projection in which the stress metric that is being counted is represented by the geometric distance between stress states. Following the same basis as API 579 and ASME VIII Division 2 this MWB metric is the equivalent stress. This relational phase information must be maintained through the signal processing and incorporated into the determination of the peak stress range estimation in order to correctly apply the API 579 fatigue equations.


High Frequency Fatigue and Using Frequency Domain Techniques

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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