Crack growth behaviour of open-hole specimens of Ti/GFRP laminates under fatigue loading

In the present paper, the fatigue damage behaviour of fibre metal laminates based on a titanium alloy and glass fibre-reinforced polymers (Π/GFRF) as Ti/FRP system was investigated in detail Static tensile tests and tensile-tensile fatigue tests were conducted on open-hole specimens of these laminates that were assembled by bonding Ti alloy sheets and GFRP plates. The fatigue damage modes of the Ti/GFRP during the tests were observed. From the experimental evidence, the dominant damage modes were identified as cracks in the Ti layer, delaminations between the Ti layer and the adhesive layer, transverse cracks in the 90° layer and 0°/90° interlaminar delaminations in the GFRP layer near the open-hole. A finite element model that represents these fatigue damages in the laminates was developed based on the damage observations. The model predictions were compared to experimental results for the stiffness degradation. The model was able to capture the stiffness reduction trends for the Ti/GFRP. This result indicated that this model could be considered to be available to predict the mechanical properties of the Ti/GFRP. Then, the stress intensity factor at the crack tip in the Ti layer was also evaluated by using this finite element model. The calculated stress intensity factor at the crack tip of the Ti layer of the laminates kept almost constant with the crack growth. From these results, it was shown that the stress concentration at the crack tip was reduced by the GFRP layer, and then, the cracks in the Ti layer exhibited the stable growth by following the Paris's law relationship.