Research On Preparation Process And High-velocity Impact Performance Of Double-layer K-cor Sandwich Structure

K-cor sandwich structure is a kind of composite sandwich structure which is strengthened in Z-direction by Z-pins.It has the advantages such as high specific strength and strong designability.So K-cor sandwich structure has a broad development prospect in aerospace,transportation and other fields.Aiming at the design characteristics of high-velocity impact protection structure,a double-layer K-cor sandwich structure was proposed in this paper.A high-velocity impact experiment was conducted to evaluate the high-velocity impact performance of the double-layer structure,and its failure mechanism and damage behavior under high-speed impact were also analyzed.Then,a finite element model of high-velocity impact process of double-layer K-cor sandwich structure was established.The reliability of the finite element model was verified by experimental data.Finally,the finite element model was used to study the influence of materials and structural parameters of double-layer K-cor sandwich structure on high-velocity impact performance,and the structural design method to enhance the high-velocity impact performance is obtained.(1)Aiming at the existing production technology,the forming method of K-cor sandwich structure was improved,and the test samples were prepared by the method of vacuum bag curing.The ballistic limit velocity obtained from the high-velocity impact test was used to characterize the high-velocity impact performance of the double-layer K-cor sandwich structure.The influences of materials and structural parameters such as two-layer structure,Z-pin implantation and foam model on the ballistic limit velocity were analyzed.The results show that the double-layer structure had stronger high-speed impact performance than the single-layer structure.Z-pin plays a dual role of failure energy absorption and dispersion propagation of stress waves in high-velocity impact process.Foam density has little effect on high-velocity impact performance.(2)The finite element model was established which corresponded to the high-velocity impact experiment,and the simulation results of ballistic limit velocity and damage condition of the model were compared with the results of high-velocity impact experiment.The results show that the ballistic limit velocity obtained by finite element analysis increases compared with the experimental value.The simulated value deviation of the double-layer structure is larger,and the maximum deviation of simulated values is 14.73% higher than the experimental value.The whole process of impact in simulation takes about 150?s,which is close to the 163?s in experiment.The impact process and damage form of the simulation results are consistent with the experiment results.All these above verify the reliability of the model.(3)Based on the reliability of the model,the high-velocity impact response of the double-layer K-cor sandwich structure was further analyzed.The influence of materials and structural parameters of the double-layer K-cor sandwich structure on the high-velocity impact performance was studied.The results are shown as follows: 1.The middle panel of the double-layer K-cor sandwich structure has the most obvious effect on the deceleration of the impact body,and the foam core has better deceleration effect on the projectile in the double-layer structure than the single-layer structure.2.The energy consumption in the damage of the panels is the most important form of energy absorption,which is much higher than the energy consumption of foam and Z-pin.The double-layer K-cor sandwich structure of the glass fiber composite panels has better high-speed impact performance than that with carbon fiber and Kevlar fiber panels.The thickness distribution has limited influence on the high-velocity impact performance of the double-layer K-cor sandwich structure.The increase of total thickness of the panels will greatly increase the energy absorption of the structure.But at the same time,weight of the structure will be significantly increased.3.Increasing the implant angle(0°~45°),the implant density and the diameter of Z-pin can improve the high-velocity impact performance of K-cor sandwich structure.Increasing the implant density of Z-pin is the most effective method.4.Increasing the distance between the middle panel and the front panel can improve the high-velocity impact performance of double-layer K-cor sandwich structure,but the improving effect is limited.