A new constant amplitude equivalent principal component analysis-based method for non-proportionality quantification of variable amplitude loaded welded joints in large-scale structures

The levels of non-proportionality in fatigue stress-time series are difficult to determine. Approaches from literature are not easy to interpret and predicts different levels for variable and constant amplitude stresses. In this paper, an extension to the PCA-based method is proposed in which variable amplitude stresses are transformed into equivalent constant amplitude stresses by scaling the stress reversal points. This ensures robust and easily interpretable results. The proposed method is compared with other approaches given in literature using published experiments and a designed offshore jacket structure. The results show that the proposed method can predict the levels of non-proportionality accurately.