Tensile strength of tapered composite structures

The tensile strength of tapered composite laminates with multiple internal ply drop steps is investigated. Both experimental testing of glass-epoxy coupon specimens and finite element modeling of the tapered region are conducted. The average stress concept is applied to outof-plane stresses from a three-dimensional finite element model. Delamination failure criteria are then used to predict strength based on ply failure and interply resin failure. Strength predictions based on interply resin failure, using a stress averaging distance of one ply thickness, are found to correlate well with the experimental results. Delamination in the tapered laminates is due to interlaminar shear failure of the interply resin surrounding the last ply drop step.