Strain-Energy-Release Rate Analysis of Delamination in a Tapered Laminate Subjected to Tension Load

Abstract

A tapered composite laminate subjected to tension load was analyzed using the finite element method. The {[07/(±45)]/1[(±45)3]/[0/(±45)/0]}5 glass/epoxy laminate has a (±45)3 group of plies dropped in three distinct steps, each 20 ply-thicknesses apart, thus forming a taper angle of 5.71 degrees. Steep gradients of interlaminar normal and shear stress on a potential delamination interface suggest the existence of stress singularities at the points of material and geometric discontinuities created by the internal plydrops. The delamination was assumed to initiate at the thin end of the taper on the-45/+45 interface indicated by the arrow in the laminate layup and the delamination growth was simulated in both directions, i.e., along the taper and into the thin region. The total strain-energy-release rate, G, and the mode I and mode II components of G, were computed at the delamination tips using the virtual crack closure technique. In addition, G was calculated from a global energy balance method. The strain-energy-release rate for a delamination growing into the thin laminate consisted predominantly of mode I (opening) component. For a delamination growing along the tapered region, the strain-energy-release rate was initially all mode I, but the proportion of mode I decreased with increase in delamination size until eventually total G was all mode II. The total G for both delamination tips increased with increase in delamination size, indicating that a delamination initiating at the end of the taper will grow unstably along the taper and into the thin laminate simultaneously.