Mode I fatigue delamination of Zanchor-reinforced CF/epoxy laminates

The Zanchor process is a novel through-thickness reinforcement technique in which in-plane yarns are entangled with each other using special needles. Mode I interlaminar fatigue crack growth behavior was investigated in carbon fiber (CF)/epoxy cross-ply laminates with Zanchor reinforcement. The laminates were molded with a Zanchor-reinforced CF dry fabric through resin film infusion (RFI). Delamination fatigue tests were carried out using double cantilever beam (DCB) specimens. The threshold values of the maximum energy release rates, GImaxth, under R = 0.1 were 70 J/m2 for Zanchor 0 (base laminate without Zanchor reinforcement) and 240 J/m2 for Zancor 2 (the density of Zanchor reinforcement is twice as high as the unit density), respectively; those under R = 0.5 were 80 J/m2 for Zanchor 0 and 400 J/m2 for Zancor 2, respectively. Thus, the threshold values for Zanchor 2 were about 3.4–5 times higher than those without Zanchor reinforcement. This increase induced by Zanchor reinforcement is almost the same or higher than that obtained under static loading (3.5 times). It is common that the increase in the fracture toughness, GIc, induced by replacing the matrix resin with a tougher system only partially contributes to the increase in the fatigue threshold, GImaxth. On the other hand, the increase in GIc induced by Zanchor reinforcement was fully translated to the increase in GImaxth. This is why Zanchor 2 gives one of the highest fatigue threshold values among existing toughened composite material systems. The difference between the reinforcing effects under static and fatigue loadings was discussed in conjunction with the microscopic fracture mechanism.