Delamination in composite laminates can migrate through the thickness, fromone interface to another. The “Delamination Migration” test method allows a detailedobservation of migration, and the evaluation of the parameters affecting it.Delamination migration tests conducted on specimens containing a 0°/θ interfacedemonstrated that migration is governed by the sign of the component of interlaminarshear stress perpendicular to the θ fiber direction, τ23. At a 0°/θ interface, when theshear stress sign is favorable for migration, delamination tends to propagate along theθ fiber direction, before migrating through the θ-oriented ply. The conditions at the0°/θ interface, which determine either delamination growth along the θ fiber directionor migration, were evaluated using the Virtual Crack Closure Technique (VCCT). Thestrain energy release rates in the direction of the fibers, Gf, and perpendicular to thefibers, Gm, were calculated, along with the total strain energy release rate, GT. Thecomponents Gf and Gm were then used with the shear stress sign, to account for theeffect of both parameters on delamination growth and migration. Correlation withexperimental results for 0°/60° delamination migration specimens showed that if thesign of τ23 is favorable for migration but Gf/GT is greater than Gm/GT, delaminationtends 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 theprediction of migration in the delamination migration specimen, compared to theanalysis using the shear stress sign only.
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