Experimental and numerical study on the improvement of interlaminar mechanical properties of Al/CFRP laminates

Improvement of interlaminar mechanical properties in Al/CFRP laminates, fabricated by carbon fiber reinforced plastic (CFRP) prepregs combined with Al alloy sheets, was studied experimentally and numerically. Three toughening methods including acid etching and mechanical patterning for surface treatment of Al alloy sheet, as well as addition of nanofiller (i.e., vapor grown carbon fiber (VGCF)) to the interface of CFRP and Al sheet, were investigated. Experimental results of double cantilever beam tests show the improvement on the interlaminar mechanical properties of Mode-I fracture in terms of much higher critical load P_C and fracture toughness G_IC. The highest G_IC was obtained in the specimens with the combination of acid etching on Al sheet and 10 g/m² VGCF addition, which was 41 and 6.5 times higher than those of the pristine samples without any treatment and the samples with only acid etching, respectively. Although further mechanical patterning had a positive effect for the case without VGCF addition, the minor effect was observed for the case of VGCF addition because of difficult dispersion of VGCF. Crack propagation and fracture surface were also observed to interpret the improvement mechanism. Moreover, by using the above experimental G_IC, finite element analyses were carried out based on cohesive zone model to numerically simulate delamination propagation. The numerically predicted interlaminar tensile strength of Al/CFRP laminates also shows great improvement of interlaminar mechanical properties using the above toughening methods.