Study On The Resin Infiltration Behavior And Influence Mechanism Of Strength Performance For Large-Tow Carbon Fiber

Large-tow carbon fiber（LCF）has become a hot topic in the development of civilian field in recent years due to its advantages of high cost-effectiveness and high manufacturing efficiency.Excellent wettability between resin and fiber is the basis for enhancing the interfacial properties of composites,however,the dense stacking of exponentially increasing monofilaments creates kinetic barriers for the resin infiltration,and thereby weakens the strength efficiency of LCF in composites.Therefore,this study conducts researches on the infiltration behavior of LCF based on the single fiber/fiber bundle contact angle method,and small-tow carbon fibers（T700,T800）are used for comparison.The characterization methods,influencing factors and optimization methods of wettability are fully discussed,and the main content is summarized below:（1）Single fiber dimension:A comparative study of the dynamic wetting behavior of three monofilaments（LCF,T700 and T800）is carried out by combining Wilhelmy and molecular kinetic theory（MKT）.The variation curves of forward force and equilibrium force during the advancing and receding process of single fiber in test liquids are recorded using dynamic contact angle testing（test liquids:deionized water and ethylene glycol）.The dynamic contact angle is calculated using the Wilhelmy theory.In-depth fitting analysis of dynamic contact angle at different wetting velocities is carried out using MKT to obtain accurate equilibrium contact angle（）.The precise surface energy of LCF,T700 and T800 is calculated to be 38.69,42.22 and 44.80 mN/m by using OWRK theory,respectively.The precise surface energy results are used to evaluate the fiber wettability in combination with its surface physicochemical state and adhesion tests,which are finally verified by interfacial shear strength.（2）Fiber bundle dimension:The apparent contact angle of resin droplets on LCF,T700 and T800 fiber bundles is recorded as a function of time and is combined with infiltration rate theory and tension-driven to characterize and optimize the wettability of fiber bundles.The difference in the wettability of fiber bundles is quantitatively analyzed by calculating the infiltration rate constant（K）,indicating that the accumulation of multiplied monofilaments weakened the wettability of LCF(K_LCF=0.205,K_LCF<K_T700≈K_T800).The impact mechanism of capillary wicking on the infiltration behavior of carbon fiber bundle is deeply analyzed based on the Washburn theory,and the capillary model is established to quantitatively analyze the capillary wicking of fiber bundles driven by different tensions（0～70 N）,thus compare and analyze the difference in wettability caused by changes in capillary channel area.The results show that the capillary wicking action of LCF under tension is more significant,and 50 N tension increases the capillary channel area of LCF by 3.06%,resulting in K increases by 1.5 times,which is far higher than the 0.2 times of T700 and T800(K_LCF=0.511,K_T700=0.434,K_T800=0.406).The wettability of LCF is significantly improved by applying tension to promote capillary wicking.In addition,macroscopic mechanical property tests confirm the optimization mechanism of LCF wettability by tension-driven,with 16.4%increase in NOL tensile strength and 15.8%increase in interlaminar shear strength of the composites under 50 N tension.This chapter successfully establishes the interplay mechanism between capillary model theory,wettability optimization mechanism,and mechanical properties of composites.