Study On High Velocity Impact Resistance Of Composite Sandwich Panels With Foam Core

As an advanced structural form,composite-foam sandwich structure has been widely used in aerospace field.With the promotion of "Advanced Rail Transit" key projects in China,composite-foam sandwich structure is bound to become one of the key development directions of lightweight technology for rail transit equipment in the future.Impact damage is the main reason for failure of sandwich structure.However,the composite-foam sandwich structure is very vulnerable to impact from external objects in engineering applications such as high-speed EMU and high-speed maglev trains.But the research results on impact resistance of composite-foam sandwich structure at domestic and foreign were mainly focused on low velocity impact,and less researches on high velocity impact with greater harm.Therefore,it is necessary to study the dynamic response and damage mechanism of composite-foam sandwich structure under high velocity impact.In this thesis,the sandwich panel with Carbon Fiber Reinforced Plastic(CFRP)facesheets and Polymethacrylimide(PMI)foam core is chosen as the research object.And research method combining experimental research,theoretical research and numerical simulation analysis is used.In order to reveal the failure process,energy absorption characteristics and damage mechanism of composite-foam sandwich structure under high velocity impact,the following work has been carried out:1)A series of high velocity impact experiments are carried out on the compositefoam sandwich panels in the velocity range of 107.34～211.54m/s by using the onestage light-gas gun experimental platform.The variation rule of the residual velocity of the projectile with the initial velocity is obtained.By analyzing the damage characteristics of the test piece,the failure modes of the composite-foam sandwich panels under high velocity impact are determined,which provides a basis for establishing and verifying the dynamic damage model of the sandwich panel;2)According to the failure mode of the test pieces in the high velocity impact test,a rate-related dynamic damage model of Fiber Reinforced Plastic(FRP)is established,in which Dynamic Increase Factor(DIF)is introduced to modify the effect of strain rate effect under the high velocity impact condition,and the three-dimensional ChangChang failure criterion based on strain is used to adapt to the failure characteristics of FRP under the impact load.Combined with the rate-related dynamic damage model of FRP,Crushable Foam Model model and Cohesive Zone Model model,a complete impact damage model of composite-foam sandwich structures is established;3)Using the general engineering simulation software ABAQUS and the user defined subroutine VUMAT,a numerical simulation analysis model of composite-foam sandwich panels is established.The simulation results show that the difference of residual velocity between simulation and experiments is no more than 7.28%,and the failure modes of the sandwich panels are in good agreement with the experimental results.These verify the validity of the simulation model.Then,the high velocity impact damage process and damage of composite-foam sandwich panels are further analyzed and discussed,and the impact energy absorption mechanism,failure type and distribution characteristics of the sandwich panels are determined;4)Parameter study of the high velocity impact characteristics of composite-foam sandwich panels is carried based on numerical simulation technology.Based on indexes such as ballistic limit,surface density energy absorption and energy absorption rate,the effects of facesheets thickness,facesheets ply and core thickness on residual velocity,energy absorption and structural damage of composite-foam sandwich panels under high velocity impact loading are discussed in detail,which provides guidance for the design of composite-foam sandwich structure.