Re-derivation of plasticity interaction for combined loading under significant levels of elastic follow-up

• Finite element analyses to optimise the level of elastic follow-up, Z.
• Existing assessment approaches not able to predict V/V0 with severe levels of Z.
• Re-derivation of V presented with different initial assumptions.
• Re-derivation of V provides an improved fit with more realistic values of Z.

It is a common need to assess crack-like defects under combined primary and secondary loads. A range of simplified methods exist to describe this interaction. Differences between these methods can be related to how elastic follow-up was treated or modelled. The work presented here compares finite element analyses under large levels of elastic follow-up to assessment methods developed for use in the R6 defect assessment procedure. It is shown that the approaches by James et al., Song et al. and Ainsworth were not always accurate for the extreme conditions considered. However, an improved fit was found from a re-derivation of the Ainsworth approach.