A New Stress-Range Distribution Model For Fatigue Analysis Under Wave Loading

For fatigue analysis under wave loading the long-term probability distribution of stress range needs to be known. The work described in this paper shows that, for any given sea-state, the short-term distribution of stress range can be closely approximated by a linear combination of two Weibull distributions. A semi-theoretical technique has been devised to derive the parameters of these distributions as functions of the spectral irregularity factor. The probability density function so obtained is shown to provide a close fit to the histograms of stress range obtained by simulation and rainflow counting. In addition, the equivalent stress ranges obtained from this model compare very favourably with those obtained by simulation, in comparison with other empirical models, thus providing an accurate method for the prediction of fatigue damage under random loading, with minimal computational effort.