Impact and fatigue damages of Ti/GFRP laminates

Recently, studies for a new kind of fibre metal laminates called hybrid titanium composite laminates or TiGr have been increasing for the application to advanced supersonic aircrafts. In these studies, however, sufficient observations of damages, especially internal ones, were not exhibited. In the present paper, the fatigue damage behaviour and impact damages of fibre metal laminates based on a titanium alloy and GFRP as Ti/FRP system was investigated in detail. At first, tensile and fatigue tests of Ti/GFRP specimens were conducted. From the experimental evidence, the dominant fatigue damage modes were identified as cracks and delaminations of the Ti layer, transverse cracks of the 90° layer and 0°/90° interlaminar delaminations in the GFRP layer near the open-hole. A finite element model based on these fatigue damage modes observed was developed, and this model was confirmed to predict the changes in mechanical properties of the laminates. The stress intensity factor at the crack tip of the Ti layer was also evaluated by using this finite element model. From the FE analysis, it was shown that the stress concentration at the crack tip was reduced by the GFRP layer, therefore, the cracks of the Ti layer exhibited the stable growth. Next, low-velocity impact tests were also conducted for the laminates with single Ti layer. From the experimental results, it was found that laminates with single Ti layer at non-impacted side showed good impact resistance, and in this case, the extent of interlaminar delaminations in GFRP was dependent on damages of Ti layer presented during the impact event.