Edge Effects In Tapered Composite Structures

The tensile strength of quasi-isotropic tapered composite laminates with multpie internal ply drop steps is investigated. Both experimental testing of glass-epoxy coupon specimens and finite element modeling of the tapered laminates are conducted. The interlaminar stress states created by the free-edge effect and the internal ply drops were determined using a quasi-threedimensional finite element model of a laminate cross-section and a three-dimensional model of the tapered geometry, respectively. Both models incorporated an interply resin layer at the d lamination prone ply interface. The average stress concept was applied to the two interlaminar stress states, which were superimposed near the root of the taper, and a quadratic delamination failure criterion was used to predict delamination onset. Strength predictions based on failure of the interply resin correlated well with the experimentally determined strengths.