The Research Of Molding Process And Toughening Mechanisms Of PA-6 Dry Fiber Placement-RTM

On the background of engine composite fan blade,the dry-fiber placement and liquid molding method was studied in this paper.The study was carried out from the perspective of forming process,process simulation mechanical properties and etc.Firstly,the thermoplastic tackifying fiber which could meet the requirement of process was manufactured by powder suspension method.The bonding performance was analyzed.Secondly,the permeability of fiber preform was studied to acquire the effect of tackifier on the permeability and the numerical value of permeability.Finally,the influence and toughen mechanism of tackifier on the mechanical properties of composite was studied to provide the reference and guidance for dry-fiber placement and liquid molding’s application.（1）Thermoplastic resin PA-6 was selected as tackifier,and the process parameters and bonding performance of tackifying fiber were studied,on these basis,the tackifying fiber which meets the process requirements was manufactured.Based on impregnation model,the process parameters of thermoplastic tackifying fiber manufacture platform was determined:the dispersant removal temperature as 90℃,pre-impregnation temperature as 240℃,double steel with molding temperature of 220℃,traction speed of 10³0mm/s,traction tension of 7N.Based on these parameters,the thermoplastic tackifying fiber with different contents of tackifier was manufactured by adjusting the content of dispersant agent and its microstructure and bonding performance was analyzed.Taken both factors into consideration,the tackifier’s content of thermoplastic tackifying fiber was controlled as 8wt%.（2）Permeability of preform was measured by simulation and experiment for the liquid molding of fiber preform that prepared by dry-fiber placement.The preform was manufactured by ultrasonic consolidation and the test model to measure permeability based on Darcy law was established.The permeability was tested by experiment and corrected by PAM-RTM process simulation.The corrected permeability of fiber preform with 8wt%tackifier was compared with preform with no tackifier.The results showed that the permeability of fiber preform decreased by 55.5%and 52.0%due to the existence of 8wt%tackifier,which would affect the impregnation between fiber and resin.（3）Dry fiber placement and liquid molding specimens were prepared,and the effect of thermoplastic tackifier on composites’mechanical properties was studied.The experimental results showed that the existence of thermoplastic tackifier would result in the reduction of interlaminar bonding strength and remarkable increase of toughness of composites.With addition of tackifier,the ILSS decreased by 23.6%,which was explained by the resin adhesion decreased.The G_IC,VISC,VIS and G_IC,maxC,max increased by 60.1%and 89.3%,respectively.While theG_IIC increased by 54.1%.The improvement is due to the inhibition of interlamianr crack by thermoplastic tackifier.A lot of energy was consumed by the tackifier so the fracture toughness increased.The impact strength increased by 18.7%.The propagation of impact crack across interface is hindered by tackifier and more impact energy is absorbed.（4）Effect of process parameters and lamination types on the process of blade filling was studied through finite element simulation for composite fan blade.The blade model was established by UG and meshed by Patran.The filling time of blade was simulated by PAM-RTM.The simulated results showed that the filling time is inversely proportional to the injection pressure.When the pressure increases from 0.1MPa to 1.0MPa,the filling time would decrease by 88.2%.Proper increment of injection pressure could reduce the filling time significantly.The filling time is proportional to the viscosity of resin.When the resin’s viscosity decreases from 0.5Pa·s to 0.05 Pa·s,the filling time decreases by over 90%,so lower viscosity resin could be chose to guarantee the fully infiltration.When the laminate is quasi-isotropic,the filling time is shortest as 1220s.With the same travel distance,injecting from the thicker zone may contribute to lower injection time.So proper design of laminates and location of injecting and exuding could help to save time and improve efficiency.