| Large deployable space borne cable net antenna which originated in the 1940s and 1950s has attracted worldwide attention because of its simple structure,large flexibility and high storage ratio.The cable net structure is affected by the harsh space environment for a long time during the satellite operation,which will produce large thermal deformation and mechanical relaxation,leading to the degradation of antenna performance.In this dissertation,shape memory alloy(SMA)and cable net structure are integrated to form a shape memory cable net(SMC)structure,and key technologies such as relaxation mechanism and modeling of cable net structure under space environment effect,thermal ratcheting effect of shape memory alloy,shape maintenance of cable net antenna in orbit and experimental verification system of shape memory cable net structure are deeply studied.The main work is as follows:1)A constitutive model of shape memory cable net structure is proposed and its surface accuracy was optimized.In order to meet the requirements of in orbit shape maintenance of large-scale cable net antenna,the integration design of cable net structure and shape memory material is carried out by using the on orbit adaptive idea,and shape memory alloy wires are implanted into the cable net structure to form a shape memory cable net structure.The shape memory effect of shape memory alloy is used to drive the force and deformation under the action of temperature to adjust the surface accuracy of cable net structure.Based on Brinson model,the incremental stiffness equation of one-dimensional rod element for shape memory alloy(SMA)is established,which effectively represents the relationship between force,temperature and deformation.The constitutive model and finite element model of polymer cable element are established.Combined with the incremental stiffness equation of shape memory alloy,the finite element model of shape memory cable net structure is established by finite element integration.It lays a foundation for the profile optimization of shape memory cable net structure.The thermal deformation of the cable net structure is compensated by using the large deformation of shape memory alloy wire during phase transformation.Firstly,the temperature of each vertical cable is taken as the design variable,and the root mean square error of the reflector is taken as the objective function to establish the optimization model.Then,the objective function is processed,the second-order term in the displacement is omitted,and the reflector adjustment process is transformed into a quadratic programming problem.This method is applied to the space parabolic antennas with diameters of 2m and 10m respectively.The feasibility of the optimization method is verified by numerical analysis of the shape memory cable net structure.The simulation results show that under the environment of 140℃ and-100℃,the root mean square error of the SMC antenna with a diameter of 10m can be lower than 0.5mm after optimization.2)An experimental verification system of shape memory cable net structure is established.A multi-channel temperature closed-loop control system is proposed based on Lab VIEW for the temperature control of shape memory alloy wires.The shape memory alloy wires were implanted into the vertical cable to build a shape memory cable net antenna prototype with a diameter of 2.2m,and the normal atmospheric temperature experiment and high and low temperature experiment was carried out.The three-dimensional coordinates of the reflector nodes are obtained through the photogrammetric method.Based on the experiment results,error analysis is conducted.The effectiveness of shape memory alloy in adjusting the surface accuracy of the cable net structure is verified by the experimental results.3)A surface accuracy optimization method of shape memory cable net structure under thermal ratcheting effect is proposed.In view of the residual deformation of shape memory alloy during phase transformation,a constitutive model of shape memory cable net structure considering thermal ratcheting effect was proposed.Firstly,the thermal ratcheting effect of shape memory alloy was taken as the research object,and experimental research was carried out on the thermal ratcheting effect of alloy wire under different pretensions and different temperature ranges.The experimental results revealed the relationship between the cumulative evolution law of residual martensite and the tension decay of alloy wire,as well as the evolution law of austenite transformation temperature and martensite transformation temperature.Based on the experimental results of the thermal ratcheting behavior of NiTi shape memory alloy under temperature control,the thermal ratcheting deformation is attributed to the residual martensite deformation generated by incomplete inverse transformation.With the accumulated martensite volume fraction as the internal variable,a constitutive model that can better describe the thermal ratcheting behavior and the nonlinear transformation process is developed,and thus a constitutive model with the thermal ratcheting effect of shape memory cable net structure is established.Finally,the cable net structure considering the thermal ratcheting effect is numerically simulated,and the influence of the diameter and material parameters of the shape memory alloy wires on the surface accuracy of the shape memory cable net structure are analyzed.4)An optimization method of shape memory cable net structure in space environment is proposed.The thermal analysis finite element model of shape memory cable net structure is established.The temperature field and thermal deformation of the cable net structure in a single cycle are obtained through the finite element analysis under space radiation.The temperature is divided into n sections within the range of temperature difference,and the surface accuracy is optimized for each temperature section.The diameter and material design parameters of each alloy wires are given reasonably according to the optimization results,so that the surface accuracy of the cable net structure can be kept within a reasonable range.On the basis of surface accuracy optimization design of shape memory cable net structure in a single thermal cycle,the theoretical model of thermal ratcheting effect of shape memory alloy is introduced,and realize the surface accuracy optimization of shape memory cable net structure in the full life cycle.The simulation and experimental results indicate that the introduction of shape memory alloy can significantly improve the surface accuracy of cable net structures.The optimization of the entire lifecycle in a space environment can improve the on-orbit retention of surface accuracy. |
PDF Full Text Request