Study On Impregnation And Curing Characteristics Of Carbon Fiber Composites In Ultrasonic Vibration Assisted RTM Process

Carbon fiber composite material has become one of the main lightweight materials in aerospace and automotive fields due to its excellent specific strength and specific modulus properties.Liquid Composite molding technology is one of the main molding processes of carbon fiber composite parts,which mainly includes three key steps of preparation of prefabricated parts,resin infiltration and curing reaction.The local permeability changes during the impregnation process result in the deterioration of the infiltration effect of resin matrix on the fiber,and reduce the mechanical properties of the molded part.With the development of ultrasonic-assisted molding technology,ultrasonic vibration has been introduced into technologies such as welding,grinding and injection molding.However,the research on the technology of resin transfer molding(RTM)assisted by ultrasonic vibration is still incomplete.In this paper,ultrasonic vibration assisted process was introduced into RTM molding process to study the influence of braiding type,fiber volume fraction,cross section shape of fiber bundles and ultrasonic effect on fabric permeability.The curing characteristics of resin system treated by ultrasonic vibration and mechanical properties of molding parts were also discussed.The scientific research carried out in this paper and the important conclusions are as follows.(1)Based on the full-factor experimental method,the influences of fabric weaving type,fiber volume fraction,fiber bundle cross section shape and ultrasonic vibration on fabric permeability were studied.Ultrasound-assisted unidirectional permeability testing mold was designed and 16 groups of one-way permeability measurement experiments were carried out.Using Tex Gen modeling technology and COSMOL simulation software,the inter-bundle micro-flow process of the resin in the fabric model under different fiber bundle cross-sectional shapes and fabric structures was simulated and analyzed.Results show that the cavitation effect,acceleration effect and microjet effect of ultrasonic wave in fluid can increase the permeability of fabric.Comparing the permeability of the fiber bundle cross-section model and the permeability under the effect of ultrasound,it is found that the comprehensive effect of ultrasound may also be to increase the permeability of the fabric by deforming the cross-sectional shape of the fiber bundle.(2)Three groups of resins with different ultrasonic power vibration were used as the research objects.It carried out that Fourier Transform Infrared(FTIR)Spectrometer scanning,viscosity test and non-isothermal differential scanning calorimetry(DSC)test experiments.The apparent activation energy of epoxy resin system was calculated by Flynn-Wall-Ozawa,Kissinger-Akahira-Sunose and Boswell equations.The curing reaction model of epoxy resin system under different ultrasonic amplitude vibration was obtained by using Malek's maximal probability method.Results show that the ultrasonic effect accelerated the amine addition reaction in the resin system,which changed the curing kinetic parameters,but did not change the curing mechanism.(3)Based on the single factor experiment method,the laminates prepared by ultrasonic vibration of epoxy resin system were used as the research object.The laminates of carbon fiber composites were prepared under different ultrasonic vibration parameters of different power and vibration duration,and the mechanical properties of tensile,bending and shear of short beam were tested.Combined with DIC technology and optical microscope,the full-field strain distribution of tension and the failure mode of each specimen were analyzed.Results show that under a certain ultrasonic power,the ultrasonic vibration epoxy resin system has an optimal ultrasonic treatment time.Under the same ultrasonic duration,the tensile and bending strengths of composite materials are positively correlated with the ultrasonic power.When the ultrasonic power reaches a certain power,the tensile and bending strength are negatively correlated with the ultrasonic power.