Structural Tailoring Techniques to Prevent Delamination in Composite Laminates

An experimental study was performed to determine the effect of structural tailoring techniques such as edge alteration on the prevention of free-edge delamination. Specimens were manufactured from AS4/3501-6 graphite/epoxy and tested in uniaxial tension. Unaltered specimens served as the baseline and were compared with specimens with different edge alterations. These edge alterations include vertical ply drop, hybridization with an isotropic film adhesive, and discontinuous angle alteration, and continuous angle alteration. The onset of delamination was monitored and the ultimate strength noted. Appropriate edge alterations were determined from the results of a previous finite element analysis. Edge alteration involving a discontinuity at the internal edge of a [±15/0], laminate involving the second and fifth plies increased the ultimate strength and moderately increased the delamination initiation stress. For [0/ ±15], laminates involving discontinuous edge alterations, the effects were not as significant. The delamination stress was slightly increased; however, the ultimate strength was reduced. Postmortem analysis revealed that, in many cases, delamination did not initiate at the free edge of an altered specimen, rather the failure initiated at the internal edge. However, when a continuous angle alteration was used, delamination onset was never promoted and often delamination was prevented.