Delamination in composite laminates can migrate through the thickness, from one interface to another. The “Delamination Migration” test method allows a detailed observation of migration, and the evaluation of the parameters affecting it. Delamination migration tests conducted on specimens containing a 0°/θ interface demonstrated that migration is governed by the sign of the component of interlaminar shear stress perpendicular to the θ fiber direction, τ23. At a 0°/θ interface, when the shear stress sign is favorable for migration, delamination tends to propagate along the θ fiber direction, before migrating through the θ-oriented ply. The conditions at the 0°/θ interface, which determine either delamination growth along the θ fiber direction or migration, were evaluated using the Virtual Crack Closure Technique (VCCT). The strain energy release rates in the direction of the fibers, Gf, and perpendicular to the fibers, Gm, were calculated, along with the total strain energy release rate, GT. The components Gf and Gm were then used with the shear stress sign, to account for the effect of both parameters on delamination growth and migration. Correlation with experimental results for 0°/60° delamination migration specimens showed that if the sign of τ23 is favorable for migration but Gf/GT is greater than Gm/GT, delamination tends to propagate along the θ fiber direction and migration will not occur. Delamination can migrate only if Gf/GT is less than Gm/GT. This method improves the prediction of migration in the delamination migration specimen, compared to the analysis using the shear stress sign only.
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