Analysis Of Electro-magneto-thermo-structural Coupling Effects On Composite Laminate In Lightning Environment

Advanced composite structure has been more widely used in aviation and aerospace,especially in aircraft industry, for its advantages such as high specific strength and specificstiffeness, designability, etc. Taking multifunction and integrated design for example, it canmeet the requirements of modern aircraft. However, comparing to traditional alloy, compositehas an inherent lack of electromagnetic shielding capability for its poor electrical conductionand electrical anisotropic, which can give rise to its sensitivity to lightning, and result incatastrophic damage once it suffered lightning strike. The influence of lightning to aircraft canbe divided into two aspects, they are direct and indirect effects, repectively. The lightningdirect effects were investigated in current work, and there were several pieces of content listedas follows:Firstly, lightning tests were conducted to investigate the behaviors of classical stiffenedcomposite panel suffered lightning strike. The process of interaction between the lightningchannel and the panel were studied qualitatively. The damaged area of composite surfacecaused by lightning strike was zoned into five areas, they were lightning initial attachmentarea, attached conduction area, attached expansion area, lightning reattachment area andswept damage area, respectively. The damage characteristics of six specimens of stiffenedcomposite panel were discussed in detail. The specimens were protected with four kinds ofmethod, they were partial spraying aluminum specimens, full-scale spraying aluminumspecimens, copper grid protected specimen, and reference specimen without protection,respectively.Secondly, the physical environment of composite subjected to lightning strike wasinvestigated by theoretical and numerical methods, especially the electromagneticalenvironment. The electromagnetic field of composite laminate suffered lightning current withdouble exponential impulse waveform was simulated by establishing3D finite element modelconsidering lightning environment. The results of FE-method agreed well with theelectromagnetic theory. However, the theory was extremely complex and not intuitive. On thecontrary, the numerical results can directly reflect the distribution characteristics ofelectromagnetic field of composite laminate, and directly reflect the influence of lightningchannel on the electromagnetic field of composite laminate.Thirdly, the influence of electromagnetic force on the structural response of composite laminate in lightning environment was studied. The stress and displacement of compositelaminate induced by electromagnetic force merely caused by the conduction current inlaminate were compared to the stress and displacement of composite laminate considering theinfluence of the electromagnetic field of lightning channel on the electromagnetic force. Thenext case was the response of laminate caused by thermal expansion of composite induced byJoule heating of lightning current conducted in laminate without considering the influence ofelectromagnetic force. The last case was the response of laminate considering the influencesof electromagnetic force and Joule heating simultaneously. Comparisons were made betweenthe stresses and displacements of the last two cases. Comparisons and analysis showed thatthe influence of electromagnetic force on the response of composite laminate subjected tolightning strike can be ignored.Fourthly, a nonlinear dynamic material model was estabilished for studying the dynamicresponse of composite suffered lightning strike, based on elastic constitutive model andelastic-plastic failure model of composite, and high explosive burn model. A comprehensivesimulation procedure combining coupled electrical-thermal analysis and BLOW-OFF impulse(BOI) analysis was conducted to investigate lightning direct effects on dynamic damagebehavior of composite laminate. Viewing from the point of qualitative analysis for lightningdamage of composite, the results of the comprehensive analysis agreed well with that oflightning test. It can be concluded that the nonlinear dynamic material model and thecomprehensive analysis procedure were suitable for the BOI analysis of composite subjectedto lightning strike.Lastly, a usermat subroutine of progressive damage analysis for3D composite modelwas compiled based on Hashin criterion and adhesive regularized method. A whole-processnumerical analysis method was employed to investigate the uniaxial compression stability andresidual strength of classical stiffened composite panel after lightning strike. Comparisonswere conducted and the results showed that there were small errors of destability and residualstrength of panel between simulation and compression test. However, the error of uniaxialcompression stiffness was bigger, because the internal damage of real panel was not taken intoaccount in numerical simulation.