Research On High Velocity Impact Damage Of Ti/CFRP/Ti Sandwich Structure

Composite aerostructures in the course of service often suffer many kinds of high velocity objects. The relative velocity and impact energy are high, which produce impact damage to these parts. Then the performance of aircraft is affected. The serious damage may even cause a disastrous effect on the plane. In this thesis, some research was carried out based on high velocity impact damage of plane structures using composites. Ti/CFRP/Ti sandwich structure, a new type of composite material, was studied and manufactured. The damage threshold and damage status of this structure were obtained by high velocity impact tests. Comparing the damage status with that of pure carbon fiber composite materials, high speed impact damage mechanism of Ti/CFRP/Ti sandwich structure was studied. The finite element simulation method was used. All the studies were the basis for Ti/CFRP/Ti sandwich structure in the application fields of aerospace and aviation.The technological parameters for making Ti/CFRP/Ti sandwich structure were adopted by studying the influence of the titanium alloy surface treatments and types of adhesives on the adhesion properties of the composite materials and titanium alloy joints. Sodium hydroxide alkaline anodized surface treatment for titanium alloy was used and J272 epoxy film was selected so that Ti/CFRP/Ti sandwich structure specimens were prepared successfully.The impact tests for Ti/CFRP/Ti sandwich structure were carried out by using air cannons test system. The critical velocity of passing though the structure was determined. The damage situation was analyzed. Shear plugging of the front titanium sheet, tearing of the rear titanium sheet, fiber breakage and brittle fracture of adhesive layer, which were the main failure modes, were found. This thesis compared high velocity impact damage of pure CFRP laminates with that of Ti/CFRP/Ti sandwich structure specimens. The critical velocity of passing though CFRP was 203 m/s, while the critical velocity of passing though Ti/CFRP/Ti sandwich structure was 341 m/s.Based on Hashin failure criterion and Johnson-Cook material model, a numericial model to simulate high-velocity impact performace and damage characteristic of Ti/CFRP/Ti sandwich structure was established by using nonlinear FEM method and coupled with ABAQUS/Explicit software. The failure process was simulated. It turned out that the calculated results were well accorded with test results.Based on above studies, several influencing factors of impact response were discussed such as impact velocity, size of the projectile, layup of the core and thickness configuration of front and rear titanium sheets. The results were as follows. Energy absorption of the target plate tended to a stable value after the plate broke down. The structure damage had less correlation with the layup changes of the core. Ti/CFRP/Ti sandwich structure had the best ability to resist damage when the front titanium plate thickness on the premise of constant surface density increased.