Design And Mechancial Properties Of Composite Honeycomb Sandwich Structure Based On The Tailor-Folding Method

Advanced lightweight composite structure is developed for the purpose of reducing weight,increasing the loading efficiency and ensuring the structural stability in the harsh service conditions,so as to guarantee high-precision detectivity of sophisticated space vehicle.Carbon fiber reinforced honeycomb possessing the advantages of lightweight,high specific stiffness,high specific strength and low thermal expansion coefficient has important applications in advanced spacecraft components,such as satellite antenna reflector,space telescope and high-precision optical support platform.In this paper,we carry out the research work of structural design and fabrication method,mechanical characterization and evaluation of carbon fiber reinforced honeycomb sandwich structure.In the introduction,the research significance for fiber reinforced honeycomb is discussed,the mechanical properties and applications of fiber reinforced honeycomb sandwich structure are summarized,and the key scientific problems requiring solutions were extracted.In this paper,a fabrication process based on the tailorfolding method is proposed.It has the advantages of flexible structural design,controllable honeycomb shape and automated process.Lightweight,large-area and multi-configuration carbon fiber reinforced polymer(CFRP)honeycombs can be fabricated by this method.For studying basic mechanical properties of CFRP honeycomb,the theoretical models of CFRP honeycomb under flat pressure and outof-plane shear load were derived and the failure mechanism maps drawn.Out-ofplane compressive test and out-of-plane shearing test were carried out.Compressive buckling,compressive crushing and mixed failure are observed in out-of-plane compressive test.Shear buckling and shear fracture failure were observed in out-ofplane shearing test.The ultimate load-bearing capacity and failure mechanism of CFRP honeycomb sandwich structure was obtained by observing the failure process,analyzing the energy absorption performance and comparing with other honeycombs.The mechanical properties of CFRP honeycomb were added into the Ashby material selection map and fill the blank of mechanical properties of engineering materials.CFRP honeycomb sandwich structure as the structural unit of spacecraft structure,mainly bears three-point bending load and lateral compressive load.The mechanical responses become more complex as the structural parameters of CFRP honeycomb sandwich structure increases.In this paper,the theoretical models of CFRP honeycomb sandwich structure under three-point bending load and lateral compressive load are derived respectively.Three-dimensional failure mechanism maps were drawn to analyze the influence of structural parameters,ply stacking sequence and payload type on the failure modes of CFRP honeycomb sandwich structure.Under the three-point bending load,the layer method of CFRP honeycomb has a greater effect on the mechanical responses of the sandwich structure.The sandwich structure with 0°honeycomb show large deformation due to the plastic yield of matrix,and possess five failure modes,including intracellular dimpling,face fracture,core shear buckling,core shear fracture and debonding.The sandwich structure with 45°honeycomb show higher flexural stiffness and ultimate load due to the reinforcement of fiber,and possess five failure modes,including intracellular dimpling,face fracture,core shear buckling,core collapse and debonding.Under lateral compressive loading,the effect of layering method in CFRP honeycomb on the mechanical responses of sandwich column is very small and can be ignored.The sandwich column with 0 ° honeycomb possess four failure modes,including intracellular dimpling,face fracture,shear macro-buckling and debonding.A rainbow contour map of the load-carrying ratio is drawn by nondimensional structural parameters,structural mass and load equation.Combined with failure mechanism maps,the geometrical relation equation of the optimal structural design path of sandwich structure under three-point bending load and lateral compressive load were obtained.It was found that debonding failure mode limit the upper limit of the loadbearing efficiency.In order to improve the upper limit of load-bearing efficiency and develop the potential of lightweight structure,the interfacial reinforced CFRP honeycomb is designed by modifying the tailor-folding method.The interfacial reinforced CFRP honeycomb,which has a strengthening platform connected with the honeycomb core and face sheet,greatly increases the bonding area without excessively increasing the density of the honeycomb core.In this paper,two types of interfacial reinforced honeycombs are designed.The mechanical responses of sandwich structures with Itype crack are measured by the double cantilever beam tensile test.The critical strain energy release rates of different honeycomb sandwich structures were calculated by the modified beam theory and the elastic foundation theory,respectively.The failure mode and strengthening mechanism of the interfacial reinforced CFRP honeycomb are analyzed.It is found that the bonding property of hexagon CFRP honeycomb is lower than that of commercial honeycombs made by other materials,but the bonding property of interfacial reinforced honeycomb has been greatly improved,which is comparable to microporous aluminum alloy honeycomb and exceeds most commercial honeycombs.The debonding failure mode regions of the interfacial reinforced honeycomb and hexagon honeycomb in the lateral compressive failure mechanism maps is compared.It was confirmed that the bonding ability of the interfacial reinforced honeycomb is greatly improved.Many components of spacecraft vehicle require sandwich structures with complex three-dimensional surfaces to meet the aerodynamic and radar detection functions.In order to solve the critical problems of that too large flexural stiffness and the saddle-shape deformation surface of CFRP honeycomb,where reduce the structural accuracy of curved sandwich shell,a flexible and deformation controllable CFRP honeycomb was designed by curved-wall method.Several flexible honeycomb configurations are proposed,but curved-wall hexagon honeycomb and Jellyfishshaped honeycomb are intensively studied.The theoretical model of flexural honeycomb is deduced for in-plane stiffness,Poisson’s ratio and bending surface.It is found that the in-plane stiffness of the flexural honeycomb is only 1/14 of that of the straight-wall honeycomb under the same density.The in-plane stiffness of the flexural honeycomb fabricated by CFRP is similar to that of the commercial aluminum honeycomb,which meet the performance requirement of engineering application.The effects of critical structural parameters,including intersection angle,chord length ratio and radian angle of honeycomb wall,on the in-plane mechanical properties of honeycomb were studied.A testing device was designed to measure outof-plane bending surface of honeycomb for obtaining the z-direction displacement cloud map and comparing with the contours of a theoretical surface.The geometric parameters combination with same mechanical properties in principle directions and the range of mechanical properties are obtained.The honeycomb configurations which are suitable for two-dimensional surface and rotating paraboloid is founded.