The Research Of Lightning Damage Of Carbon Fiber Reinforced Polymer Composite

As a new kind of composite material, carbon fiber reinforced polymer (CFRP) which has high strength, low density, corrosion resistance and other characteristics, is widely used in aeronautics and astronautics sector. Especially in commercial aircraft, the application amount of CFRP is much higher due to their excellent properties. Considering the situation that flying in the air, the lightning protection method of plane is not in lightning avoiding but defending. According to relevant statistics, the commercial aircrafts may have suffered a lightning strike each year, and especially, the probability of lightning strike will be lager in rainy area. However, the conductive performance of CFRP is not as good as metal materials, and a lightning storm may pose a threat on the safety of the flight. The security of the plane that contains large amount CFRP attracts more and more attention of the aerospace departments. In order to realize "large aircraft" plan in our country, large-scale use of CFRP materials is the key point. The study of the lightning damage issue of CFRP is of vital significance in guarantee the application safety in the aerospace.In this paper, lightning damage process of CFRP is studied by FEM (Finite Element Method) and experiment. The temperature field, the degrees of pyrolysis, damage factors and mechanism of CFRP lightning damage is studied in the combination of FEA and experiment.In this paper, FEA model established by commercial FEM software ANSYS based on the theory of coupled thermal-electric field to calculate temperature field and its change rules after CFRP laminated plates subjected to lightning. Firstly, the temperature field during lightning is obtained and inherited to calculate the heat dissipation temperature field after lightning. The time scale cross problem which has difficulty in convergence is solved in the way. Secondly, pyrolysis kinetics model of CFRP is coded by APDL subroutines and realized the calculation of degree of pyrolysis in ANSYS by unifying temperature field and pyrolysis kinetics equations. Thirdly the method of calculating CFRP lightning damage is suggested, that the damage area and depth of the lightning can be calculated by isotherm and pyro lysis degree respectively which have good agreement with experiment results. Various factor and their relationship related to lightning damage is researched through damage area and depth. Results are as follows:(1) The surface of CFRP suffers the worst damage with45°long and narrow strip area after the lightning. The temperature field of each layer of CFRP is affected by heat conduction of the adjacent layers except joule heat produced by itself and the temperature morphology reflects carbon fiber angle characteristics both itself and adjacent layers.(2) After lightning, the high temperature area of CFRP will not obviously increase and isothermal tend to be oval shape gradually and finally into round and disappear during free cooling stage after lightning.(3) The temperature of lightning point arises fast, then decreases slightly and remains above3000℃in30μs in the lightning process, however it will almost drop to room temperature after30s.(4) The highest temperature CFRP laminate is on the route of lightning strike point depth, temperature arises from outside to inside and extends to the direction of depth in the process of lightning, and the internal temperature is higher than internal temporarily in cooling stage, then almost down to room temperature after30s.(5) The degree of pyrolysis of CFRP system is affected by the temperature, heating rate, and pyrolysis time. The higher the temperature, and longer pyrolytic time is, the greater degree of pyrolysis is. However, faster heating rate has a lag effect on the pyrolysis.(6) CFRP lightning damage is related to many factors, such as peak current, wave, charge, action integral in lightning electrical parameters and conductivity, thickness, fiber volume, size etc. in the view of material science. The action integral and conductivity are the most important external and internal cause repectively, thereby the best way to reduce lightning damage is improve the electrical conductivity of CFRP.In the paper CFRP is tested by artificial simulated lightning in experiment. CFRP structure is produced, carbon fiber volume fraction is tested according to the national standard, test-bed is designed, produced artificial lightning current to test of CFRP by impulse current generator, then detect lightning damage through ultrasonic C-scan and ultrasound B-scan and microstructure by SEM. Conclusions are as follows:(1) A loud noise is produced during simulated lightning subjected to the CFRP, and fiber fracture bombe, resin pyrolysis, gas release, delamination, damage pit take place.(2) The current peak of artificial lightning has a great influence on the lightning damage on morphology and area, the greater the peak current results in larger damage area in ultrasonic C scan and the greater damage depth in B-scan.(3) The microstructure of the lightning damage has following characteristics: carbon fiber fracture, bending, coarsening, erosion, surface resin, pyrolysis and carbonization, sometimes residue carbon attached to carbon fiber surface to be visible.(4) CFRP lightning damage includes damage pit and delamination. The damage pit is results from resin pyrolysis, gas overflow, fiber erosion, fracture and raise. Delamination damage reasons mainly include the loss of interlayer adhesion strength after resin pyrolysis, layer open by gas expansion and thermal stress.