Micro-Deformation Behavior Of T700 Carbon Fiber Tension Cable In Large Cable-Net Antenna

In this dissertation,a thermomechanical load and deformation test facility was developed based on the dimensional stability of large deployable cable-net antenna with high precision.The strain relaxation deformation regularities of T700 carbon fiber tension cable under cyclic loading of 20 N to 80 N and the thermal expansion deformation regularities in the temperature range of-150°C ~ +150°C were studied.The microstructures of tension cable before and after deformation were analyzed by scanning electron microscopy(SEM),transmission electron microscopy(TEM),Raman spectroscopy(Raman)and X-ray diffraction(XRD).The strain relaxation activation energy of tension cables was measured,and the micro-deformation mechanism of tension cables was discussed.The results of cyclic loading strain relaxation test show that the cyclic loading and unloading curves of T700 carbon fiber tension cable do not coincide,and the stress-strain curves show a typical hysteresis loop.With the increase of cyclic loading times and temperature,the hysteresis loop gradually shifts to the right,and the strain relaxation of T700 carbon fiber tension cable is the largest in water medium and the smallest in vacuum environment.There is obvious internal friction in the process of cyclic loading and unloading.The internal friction value decreases rapidly with the increase of the number of cyclic loading and unloading.In air and vacuum environments,the internal friction value of tension cables is the smallest at-150 °C,and the maximum is at 25 °C.On the other hand,the nominal loading modulus and the nominal unloading modulus of the specimens also increased with the increase of cyclic loading and unloading times.Comparing the nominal modulus of loading and unloading at different temperatures,it is found that the nominal modulus of loading and unloading of tension cables is the largest at-150 °C.By fitting the test data,the activation energies of strain relaxation of T700 carbon fiber tension cable in air and vacuum are 1.52 kJ/mol and 1.36 kJ/mol,respectively.The micro-deformation mechanism of T700 carbon fiber tension cable is the unsynchronized and unbalanced force between inner carbon fibers of tension cable and the mechanism controlled by the weak junction force between fibers.Thermal expansion test results show that the T700 carbon fiber tension cable has obvious negative expansion characteristics in the range of-150°C ~ 150°C,and the strain variations during the heating and cooling stages are not consistent.The microstrain-temperature curves of the specimen show obvious hysteresis loop.With the same thermal cycles,the coefficient of thermal expansion decreases with the increase of load.Under the same test load,the coefficient of thermal expansion increases with the increase of thermal cycles.The coefficient of thermal expansion of T700 carbon fiber tension cable was basically unchanged after exposure to hygrothermal and vacuum ultraviolet irradiation,but slightly decreased after electron irradiation.Among the thermal expansion deformation of tension cables,the creep deformation under 20 N load accounts for 2.48%,and the creep deformation under 60 N load accounts for 12.86%.The main reason for the decrease of thermal expansion coefficient of T700 carbon fiber tension cable specimen is the slight increase of the degree of structural order and the degree of orientation.