EFFECT OF PLY-DROP CONFIGURATION ON DELAMINATION STRENGTH OF TAPERED COMPOSITE STRUCTURES

Delamination suppression by altering the sequence of ply drops is eval uated for tapered glass/epoxy laminates. Two different stacking sequen ces with thin section layups of [0(4)/145(2)](s) and [+/-45(2)/0(4)]s containing drops of three sets of +/-45-deg plies are investigated. A finite element model using three-dimensional solid elements is constru cted to evaluate the state of interlaminar stress in and around the pl y drops. The effect of the stress-free edge is considered by providing a mesh refinement near the free edge. Tapered specimens are manufactu red and tested under quasistatic uniaxial tension. For specimens of [0 (4)/+/-45(2)](s) stacking sequence, delamination strength is dependent on the ply-drop sequence, and structural tailoring of the ply drop re gion results in a reduced interlaminar stress state and an associated increase in delamination strength. Structural tailoring, however appea rs to be ineffective in the [+/-45(2)/0(4)](s) specimens. The measured delamination strengths are insensitive to the ply-drop sequence, alth ough the finite element model indicates a stronger sensitivity. In gen eral, the finite element model correlates well with the data. The meas ured differences in strength among the [04/+/-45(2)](s) specimens and the overall strength difference between the [0(4)/+/-45(2)](s) and the [+/-45(2)/0(4)](s) specimens are predicted by the finite element mode l using strength criteria on the stress state in the interply resin re gion.