Influence of through-thickness reinforcement aspect ratio on mode I delamination fracture resistance

Interlaminar reinforcement may be achieved in a composite laminate by the insertion and bonding of stiff rods through the thickness. It is experimentally shown in the paper that increased aspect ratio (AR) of through-thickness rods significantly elevates mode I maximum delamination fracture resistance of a laminate. This effect is explained through the analysis of rod/laminate interfacial stress transfer. Lower interfacial shear stresses occur for interlaminar rods of greater AR for equivalent bridging traction against opening delamination. Thereby, a larger AR allows the rod to develop a greater closure force prior to the rod debonding from the laminate. Further, these results show that this approach for interlaminar reinforcement is best applied to laminates of thickness-to-rod diameter ratio sufficient to allow for insertion of high aspect ratio reinforcement rods.