Research On The Anti-damage Performance Of UAV Composite Honeycomb Sandwich Airframe Structure

Unmanned aerial vehicle(UAV)has been favored by countries because of its reusability,excellent stealth,reconnaissance and attack compatibility and operational flexibility.However,in recent years,military UAVs have frequently failed in the battlefield,and simple shoulder-mounted missiles can easily knock them down,and the attack and defense have exposed huge problems.Therefore,to adapt the complex battlefield surroundings,it is particularly needlessly to enhance the ability of structural defense against multiple damage targets.At present,the UAV honeycomb sandwich airframe structure is composed of two layers of carbon fiber skin and a layer NOMEX honeycomb core.When an out-of-plane load is applied to the structure the NOMEX core layer will deform and quickly reach the peak load.The delamination crack expands rapidly between the skin and the core layer,resulting in the low resistance of the structure.At the same time,in the case of high-speed fragment shear failure,the stacking energy consumption of the core layer is relatively weak,and the longitudinal tensile effect of carbon fiber skin is not reflected.Existing studies have found that when the fragment velocity is less than 10 m / s,the honeycomb sandwich of carbon-fiber and NOMEX can be broken down.Therefore,for penetration the high-speed damage element,its protective ability is not ideal,only meeting the requirements of lightweight.The damage resistant design of honeycomb sandwich structure has attracted more and more attention.Compared with the sandwich structure,honeycomb sandwich structure has better energy absorption effect and it is difficult to extended crack,which makes it increasingly widely used in the structural protection.In this dissertation,solving the problems of single structure,weak core strength and insufficient protection ability of UAV honeycomb sandwich airframe,a composite honeycomb sandwich structure is proposed based on equivalent theory and deformation failure mechanism of sandwich structure under the premise of satisfying structural lightweight.By combining theoretical analysis,simulation research and experimental study.Researching on the deformation mechanism of newly structure and the dynamic failure of structure under load,which provides a new idea for the structural design of UAV honeycomb sandwich airframe.The specific research contents of this dissertation are as follows:(1)Based on the problem of insufficient protection ability of UAV honeycomb sandwich airframe structure,this dissertation designs a composite honeycomb sandwich airframe structure.This structure ensures the same thickness and lightweight conditions as the existing honeycomb sandwich airframe structure,changes the single core bearing mode of the existing airframe structure,and finally obtains a new composite honeycomb sandwich airframe structure with obvious energy absorption characteristics of double core,multi-skin bearing and high strength honeycomb core.(2)Based on the research sandwich plate equivalent elastic parameter theory,honeycomb plate theory,equivalent plate theory and flat-nosed projectile penetrating target theory,this dissertation deduces the calculation formula of residual penetration velocity of fragment penetrating composite honeycomb sandwich structure.This method can effectively evaluate the energy absorption characteristics of structures.(3)To make the modeling process easy,this dissertation obtains the simulation calculation model of composite honeycomb sandwich structure with controllable structural parameters through parametric modeling method,and conducts simulation research on the anti-damage performance of composite structure by using LS-DYNA software.The influence of cell size,composite mode and other factors on the protective performance of composite honeycomb sandwich structure was obtained.(4)In view of the dynamic response of the composite honeycomb sandwich structure under impact load,this dissertation conducts the drop hammer impact experiment on the composite honeycomb sandwich structure.The variation laws of displacement,force,energy,residual velocity and other curves related to structural resistance and time variables are analyzed,and the differences between the protective performance of composite honeycomb sandwich structure and the existing airframe structure are compared and studied.(5)In order to analyze the anti-damage performance of composite honeycomb sandwich structure,the experimental study of fragment penetrating composite honeycomb sandwich structure at different speeds and angles is carried out,and the accuracy of the theoretical model and the calculation formula of fragment residual are verified according to the experimental results.It is found that the anti-damage performance of the composite honeycomb sandwich structure is better than that of the existing honeycomb sandwich airframe structure.In different penetration speeds,the energy absorption per unit volume of the structure is 27.2%-84.2% higher.The average error between theoretical calculation and experimental results of fragment residual velocity is within 6%,and the error between theoretical and simulation is about 8%.At the same time,the composite honeycomb sandwich structure and structural parameters with the best energy absorption characteristics are obtained.and structural parameters with the best energy absorption characteristics are obtained.