Research On Lightning Strike Damage And Protection Of Carbon Fiber Reinforced Polymer And Its Structures

Carbon fiber reinforced polymer(CFRP),because of its characteristics of light weight,high strength,antifatigue,vibration reduction and strong designability,is widely used in the manufacture of aircraft structural parts such as front fuselage,resistance plate and rectifier panel.However,when airplane is struck by lightning,due to the poor conductivity,heat conduction and electromagnetic shielding performance of CFRPs,it is prone to material ablation,perforation and electronic equipment failure,which seriously threatens the flight safety of aircraft.Therefore,the lightning strike protection(LSP)design of CFRPs is very important.It is of great significance to explore the damage characteristics and mechanism of CFRPs and its structures in lightning environment,as well as the protection and ablation mechanism of protective layer,so as to realize the optimal design of lightning protective layer of CFRPs and ensure the safe flight of aircraft.In this paper,the lightning strike damage and protection of CFRPs and its structures were studied by means of combining experiment and finite element method(FEM)simulation.Firstly,the lightning strike process of CFRPs with expanded copper mesh(ECM)protective layer was simulated,which quantitatively analyzed the protective effect of ECM and reveal the protective mechanism of the protective layer.Meanwhile the ablation characteristics of the protective layer was explored.Secondly,the lightning test of CFRPs with metal fasteners was carried out to study its damage characteristics and analyze the damage mechanism.Finally,the damage mechanism was confirmed by simulation,and the influence of many factors on the damage was explored.Then lightning protection effect of aluminum coating on the CFRPs with metal fasteners was analyzed.The main research contents and results are as follows:According to the lightning strike process and material characteristics,the lightning arc model,metal ablation model and composite pyrolysis kinetic model were established.The damage of the material is characterized by defining the pyrolysis degree of the composites and the ablation degree of the ECM.On this basis,with the help of the electrical-thermal analysis module of ABAQUS software,the FEM simulation of the lightning strike process of CFRPs with ECM was carried out,and the validity of the model is verified by comparing with the experiment.The FEM results show that the 0.051 mm ECM can effectively reduce the lightning damage of CFRPs.Through the analysis and comparison of pyrolysis degree field,the damage in the first layer of CFRPs protected by ECM is 64%less than that of unprotected layer,and there are only two layers of damage in the thickness direction,which is 14%of unprotected layer.The electric field distribution shows that the ECM can rapidly derive the current from the plane and reduce the current density acting on the lower layer of CFRPs,thus reducing the degree of thermal ablation of CFRPs.By analyzing the temperature curve and ablation degree field of the ECM,it is found that the phase explosion caused by the instantaneous temperature rise of the ECM is the main reason for the ablation of the protective layer under the huge energy of lightning.On this basis,the influence of increasing the thickness and coverage of ECM on the characteristics of lightning damage is studied under the same weight gain condition.The results show that both of them can reduce the lightning damage of ECM and CFRPs.Increasing the coverage can reduce the damage of ECM more obviously,and increasing the thickness can reduce the damage of CFRPs more effectively.The simulated lightning strike experiments of 20 kA,30 kA,40 kA and 50 kA for CFRPs with metal fasteners were carried out.The results show that the lightning damage occurs around the fasteners,and the damage degree increases with the increase of peak current.Under the action of 50 kA,the CFRPs has serious delamination inside,with the fiber fracture and expansion around the fastener,and the surface has deep bolt indentation,but there is no obvious thermal ablation.The FEM result of the lightning strike process of CFRPs with metal fasteners shows that the lightning current acting on the upper surface of the fastener is mainly conducted in the 0° ply when the both ends potential E=0 V,and the Joule heat generated causes the resin pyrolysis of the 0° ply.The results show that the explosion caused by the accumulation of pyrolysis gas in the interior of the ply is one of the main reasons for the delamination.The highest temperature of the fastener is only 476.1?,so there is no obvious damage.At the same time,it is found that the pyrolysis damage of CFRPs is greatly affected by the peak value of lightning current,stacking sequence and grounding mode.With the increase of lightning current peak,the pyrolysis area and depth also increase.Under the action of lightning current with a peak value of 100 kA,not only the layers around the fastener are damaged,but also the end of the fiber pyrolysis occurs damage.When the both ends potential E=0 V,multiple 0° layers are adjacent to each other,which will aggravate the lightning damage.The results show that there is no obvious pyrolytic damage of CFRPs due to the rapid export of electric current when side surfaces potential E-0 V.The lightning damage of strip specimen occurs in the surface layer,while the current redistribution of CFRPs with metal fasteners leads to pyrolysis in the inner layer,which affects the structural integrity.Therefore,adding insulating materials at the upper end of fasteners can help to reduce the lightning damage of CFRPs.At the same time,it is found that the aluminum coating on the-surface of CFRPs can also effectively reduce the lightning damage.To sum up,this paper studies the lightning damage mechanism of CFRPs from simple laminate structure to CFRPs with metal fasteners,quantifies the protection effect of protective layer through the FEM simulation,and then studies the ablation characteristics and protection mechanism of protective layer,which has guiding significance for the optimization design of aircraft lightning protection layer.