Characterizing fatigue delamination growth behaviour using specimens with multiple delaminations: The effect of unequal delamination lengths

•Interaction effects between multiple delaminations in a specimen were investigated.•Interaction effects change the value of the local strain energy release rate.•This causes the delaminations of unequal length to have unequal growth rates.•Interactions between multiple delaminations cannot be neglected in many cases.

Finite element anlysis (FEA), supported by experimental data, was performed on a common specimen for delamination growth characterisation, in which multiple delaminations were present, in order to study interactions between these delamiations. In contrast to the commonly held assumption that interaction effects between delaminations of unequal lengths can be neglected, it was found that these interaction effects are in fact significant. The FEA shows that the equal length situation is unstable; any length difference between the delaminations will grow. In addition, interaction effects can cause the false appearance of scatter when correlating delamination growth to the strain energy release rate.