| Modern space remote sensing cameras mostly use lightweight materials and methods to reduce the main reflectors'weight,which can reduce the launch costs and the difficulty of supporting structural design,as well as control the deformation of the mirror's optical surface and increase the specific stiffness of the structure.Compared with traditional glass and metal materials,carbon fiber reinforced plastic?CFRP?materials have the characteristics of low density,high specific rigidity and specific strength,light weight,low coefficient of thermal expansion,easy replication,non-toxicity,no special equipment,etc.,which make it the ideal material for mirrors'fabrication.Researches on CFRP mirrors in China are basically in the theoretical or laboratory research stage,and haven't formed systematically technical scheme for the CFRP mirror components,such as the optimal design of the CFRP mirror components,fabrication technology,and optical processing,etc.Concerning the deficiencies in current domestic related fields,this paper has systematically discussed and studied CFRP mirror and its supporting structure.The direction,sequence and thickness of carbon fiber plies will seriously affect the stiffness and surface accuracy of the CFRP mirror panels.The laminates'rigid design principles,mechanical calculation methods,and material selection of the CFRP mirror are described in detail.Through the classical laminate theory,the theoretical model of CFRP symmetrical laminates has been established.By means of regularized stiffness coefficient method combined with finite element analysis,a quasi-isotropic carbon fiber layup method has been designed as[0°/90°/30°/-60°/.60°/-30°]S,making the CFRP mirror better able to bear the gravity and thermal load,and further ensure the CFRP mirror's surface accuracy.Aiming at the CFRP mirror's requirements of high specific stiffness,surface accuracy and thermal stability,a ultra-lightweight CFRP mirror has been designed with a diameter of?360mm,semi-open back and triangular stiffener mesh structure,which is supported through three points by side of the mirror.The CFRP mirror's global and automated multi-objective optimization has been carried out through using the Isight integration software combined with Opto-mechanical integration optimization method,and the optimization takes the CFRP mirror's structural and dimensional parameters as variables,and the surface accuracy and weight are taken as optimization targets.Aiming at the influence of different supporting structures on the CFRP mirror's surface accuracy,a Bipod flexible supporting structure has been designed by using the MATLAB theoretical optimization calculation and the Opto-mechanical integration optimization method.The Bipod flexible supportting structure's sensitive dimensional parameters which influence the CFRP mirror's surface accuracy has been studied,drawing a conclusion that the Bipod flexible supporting structure's supporting position must be in agreement with the plane of the CFRP mirror's centroid.After determining the Bipod flexible supporting structure's optimal dimensional parameters,the assembled CFRP mirror components'stiffness characteristics and dynamic characteristics have been obtained through finite element analysis.Aiming at the problems of fiber print-though,mirror panel replication accuracy and coating technology in the fabrication of CFRP mirrors,a reasonable and effective dabrication method of the CFRP mirror has been proposed.The?360mm CFRP spherical mirror was fabricated by mirror replication method combined with autoclave molding and compression molding process,and an even layer of cyanate has been attached to the CFRP mirror's surface by vacuum injection molding process to effectively reduce the surface's phenomenon of fiber print-through,also,the fabrication,coating,ultra-precision process and optical grinding and polishing technology of the CFRP mirror have been systematically illustrated.The adhesion test between the CFRP mirror and its Bipod flexible supporting structure has been carried out.Aiming at the dynamic characteristics of the assembled CFRP mirror components,some dynamic tests have been conducted.The fundamental frequency and dynamic response information of the assembled CFRP mirror components have been obtained through the dynamic tests,meanwhile,the Bipod flexible supporting structure's ability of withstanding dynamic loads and the accuracy of finite element analysis has been verified through the experimental test results.This paper has systematically studied the optimal design,fabrication method,optical processing,and testing technologies of the CFRP mirror components.The optimized CFRP mirror components'surface figure error?RMS value?is better than?/50??=632.8nm?in the detection conditions which obtained by finite element analysis.The carbon fiber mirror has been fabricated by mirror replication method.The manufactured CFRP mirror's mass is only 1.85kg,and its density is 1.78g?cm-3,which has a high bending strength?300MPa?,fracture toughness(3.5 MPa?m1/2)and lower coefficient of thermal expansion(-1.23×10-6).Meanwhile,the assembled CFRP mirror components'mass is 2.45kg,and it's fundamental frequency is 362Hz.The assembled CFRP mirror components'dynamic performance is good,and the Bipod flexible support is stable and reliable through experimental tests.The surface figure error?RMS value?of the?360mm CFRP spherical mirror after grinding and polishing is 0.045?,which is better than?/20??=632.8nm?and at the leading level in China.Drawing the conclusion that the CFRP material is more suitable for ultra-lightweight mirror's fabrication,and the manufactured CFRP mirror's performance is good and the process is feasible,moreover,it can provide certain reference value for the fabrication of ultra-lightweight CFRP mirrors with larger aperture or even larger aperture in the future. |
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