Study On Shape Memory Performances And Mechanisms Of Epoxy-based Carbon Fiber Composites

Shape memory epoxy-based carbon fiber composites have been widely used in space deployable structures due to their light weight,stable deployment and excellent environmental resistance.In the process of shape memory,carbon fiber buckling and shear deformation of resin matrix will occur in epoxy-based carbon fiber composites,while the weak shear deformation ability of common epoxy resin makes poor folding ability and shape memory performance of carbon fiber composites.In this research,based on shape memory mechanism of epoxy-based carbon fiber composites and epoxy,high shear deformation epoxy with IPN structure was obtained by adjusting the content of polyurethane reversible phase,which improved the shape memory performance of resin matrix and enhanced the folding ability of epoxy-based carbon fiber composites.(1)Polyurethane terminated isocyanate groups(PPU)were prepared by the reaction of diphenylmethane diisocyanate(MDI)and poly(propylene oxide glycol)(PPG),and then grafted with bisphenol A epoxy resin to obtain epoxy resins with different content of polyurethane reversible phase(PUEP1,PUEP2 and PUEP3).The structures of PPU and PUEP were confirmed by 13C-NMR spectra and FT-IR spectra.High shear deformation epoxy resins(HSDEP1,HSDEP2 and HSDEP3)were prepared from PUEP1,PUEP2 and PUEP3.The results showed that film tensile properties and punch-shearing properties of HSDEPs were effectively improved with the increase of polyurethane reversible phase content.SEM showed that the degree of microphase separation of polyurethane increased significantly with the increase of content of polyurethane reversible phase.(2)The thermal mechanical analysis cycle properties,creep properties and shape memory properties of HSDEP1,HSDEP2 and HSDEP3 were studied.The results show that with the increase of polyurethane reversible phase,the number of thermo mechanical analysis cycles increased,and the creep property became worse,which was due to the irreversible deformation caused by the molecular chain slip and network breakage;In shape memory performance,the shape recovery ratio increased slightly,the shape fixity ratio decreased slightly and the number of shape memory cycles also increased;among them,HSDEP3 showed the best shape memory performance.The performances of HSDEP3 was dependent on shape memory cycles.The results represented that with the increase of the number of shape memory cycles,the molecular chain slippage with slight network damage of polyurethane reversible phase firstly occurred,and then a large number of network broke,resulting in the decrease of crosslinking network density and the increase of network energy loss;the morphology showed that the "spherical" micro phase separation zone of polyurethane reversible phase gradually changed into"ellipsoid" and then broke,the shape fixity ratio firstly increased and then decreased,the shape recovery ratio firstly remained unchanged and then decreased,the shape recovery time firstly decreased and then extended,the heat resistance decreased,the tensile modulus and tensile strain firstly increased and then decreased,and the tensile strength first remained unchanged and then decreased.(3)The results of folding test of HSDPCs based on HSDEPs indicated that the stronger the shear deformation ability of HSDEPs,the stronger the folding ability of HSDPCs.HSDPC3 was prepared by hot melt two-step method with HSDEP3 and shape memory performances were researched.The results showed that HSDPC3 had lower shape fixity ratio and faster shape recovery rate than HSDEP3,and the shape memory performance was dependent on shape memory cycles.With the increase of the number of shape memory cycles,damage of internal structure in resin matrix changed firstly,and then resin matrix failure,delamination and fiber breakage in warp caused by out-of-plane buckling occurred,after that,fiber breakage in weft caused by in-plane buckling was presented,and these failure led to the increase of the shape fixity ratio,the decrease of the shape recovery ratio,the extension of the shape recovery time,the decrease of the shape recovery force,and the reduction of the load-unload cycle performance,which was similar to that of the resin matrix.