A Study Of Interlaminar Toughening Of Carbon Fiber/epoxy Composites At Cryogenic Temperature

Carbon fiber reinforced polymers?CFRPs?have been widely used owing to their superior performance.The research of reusable space vehicle?RLV?is an important trend in the current field of aerospace.Cryogenic propellant tank is the main structure of RLV,whose quality and volume account for great proportion of RLV.The application of high-performance CFRPs to cryogenic tanks has great advantages for weight reduction.However,interlaminar delamination,frequently occurs due to the inherent brittleness of the epoxy matrix,which reduces the comprehensive performance of CPRPs largely.Many strategies such as Z-pinning,interfacial modification,matrix toughening and interlaminar toughening have been developed to overcome this problem.The interlaminar toughening method can greatly increase the interlaminar toughness while maintaining the other properties and original manufacturing process to a great extent,Therefore,in this study the interlaminar toughening method is used to improve the interlaminar toughness of CPRPs,and the toughening mechanism is analyzed at room temperature?RT?and cryogenic temperature?LT?.Several kinds of nano particles were synthesized and prepared,then sprayed evenly on the surface of prepregs to enhance interlaminar fracture toughness of CFRPs.ENF tests were taken to measure mode ? interlaminar fracture toughness(G_?C).The results indicated that G_?C increased with proper content of nano particles at RT,This is mainly due to the formation of microstructures which may absorb fracture energy.At LT,the G_?C of CFRPs modified with nano particles decreased,the reason is that the mode of strong interfacial stress distribution is broken due to nano particles,and the stress between fiber and resin is redistributed which weaken the interfacial bonding strength,besides,nano particles may produce defects and lead to stress concentration.Nano AlOOH performed best comprehensively.Several kinds of thermoplastic particles were used to toughen CFRPs,and G_?C were tested.The results indicated that PAEK performed best comprehensively.Micron-scale PAEK particles and nano-scale AlOOH particles were introduced into the interlayer to toughen CFRPs,The results indicated that PAEK/AlOOH had synergetic effect on toughening both at RT and LT.In order to analyze the toughening mechanism further and the effect of interlayer thickness and modulus on interlaminar fracture toughness,particles were considered as interleaf by equivalent inclusion theory,then mode ? and ? interlaminar fracture toughness finite element models were established,and the interlaminar fracture toughnesses were analyzed both at RT and LT.The calculation results matched the experiment.It's also shown that thick interleaf have better toughening effect when the interleaf's thickness are far below the thickness of prepreg.In a certain range,the interleaf's low modulus is beneficial to toughening,and the influence of the modulus is greater than that of thickness.