ANALYSIS OF DELAMINATION INITIATION IN POSTBUCKLED DROPPED-PLY LAMINATES

The compression strength of dropped-ply, graphite-epoxy laminated plates for the delamination mode of failure is studied by a finite element analysis and corroborated with experiments. The compression strength of the 2.54-cm-wide specimens, which exhibited a linear response to delamination initiation, is greater than the compression strength of the 7.62-cm-wide specimens with the same layup, which exhibited a nonlinear response to delamination. Analyses confirm that the influence of the geometric nonlinearity on the response of the 2.54-cm-wide dropped-ply laminate is insignificant, but this nonlinearity is very significant in the response of its 7.62-cm-wide counterpart. For the 7.62-cm-wide dropped-ply laminate, the decrease in compression strength is associated with the redistribution and intensification of the severe interlaminar stress gradients occurring at the dropoff to a location closer to the knife-edge support.