Study On Forming Mechanism Of R-angle Wrinkle Defect In Composite Autoclave Forming Process

Carbon Fiber Reinforced Plastics(CFRP)have many excellent properties,such as light weight,high strength,strong designability and suitable for extreme environment.In recent years,they have been favored by the aerospace manufacturing field.Among many composite manufacturing technologies,prepregate-autoclave forming process has the advantages of uniform force and high forming quality,and has become the most widely used process in the field of aviation composite manufacturing.However,the R-angle area of C-type and L-type components is prone to wrinkle defects in the process of autoclave forming,which has a serious impact on the forming quality and service performance of the components.In order to effectively reduce the occurrence of R-angle wrinkle defects and improve the forming quality of components,it is necessary to further study the formation mechanism of R-angle wrinkle defects.Therefore,this paper aims to analyze the deformation mechanism of prepreg in the R-angle region and the causes of wrinkle defects in the process of autoclave forming,and design test methods to test the two main factors affecting the generation of wrinkles--compaction of prepreg and interlayer slip behavior,so as to optimize the autoclave forming process scheme.The main research contents and conclusions of this paper are as follows:(1)Firstly,the small test parts of C-shaped beams with two different brands and layers of prepregs at home and abroad were prepared by autoclaved process,and the areas of wrinkles produced were observed by metallography.Secondly,the deformation behavior of the prepreg in the R-angle area during the C-beam forming process is analyzed,and the mechanism of wrinkle defect formation is explored.It is confirmed that the compaction and interlayer slip behavior of the prepreg are the main influencing factors of wrinkle generation.At the same time,the quantitative analysis indexes of wrinkle defects in thickness distribution,edge slip Angle and R-angle partial wrinkle are proposed,which can provide reference for defect characterization and quality evaluation of components in actual production.(2)The pressure practice of prepreg in autoclaved tank forming process was explored as follows: firstly,the viscosity temperature curve of two prepregs was measured by rotating rheometer;secondly,the compression response of prepreg under different temperatures,pressures and layers was studied by using self-designed test methods.The results show that the compaction process of the prepreg includes the initial sudden change stage,the creep stage and the thickness approaching stage at the late loading stage under the step compression and load retention tests.The compaction strain increases with the increase of temperature,but after reaching a certain temperature,the strain begins to approach a limit strain.Under 18 layers,the Cycom970 prepreg reaches a limit strain of 0.186 after 85℃,and the domestic prepreg reaches a limit strain of 0.301 after 105℃.(3)The interlayer slip behavior of prepreg during autoclave molding was explored.First,scanning electron microscopy(SEM)was used to characterize the surface morphology of prepreg at different temperatures.Second,the self-designed test device was used to test the interlayer slip resistance of two prepregs at different temperatures,different pressures and continuous temperature rise.The results show that temperature is an important factor affecting the interlayer slip behavior of prepreg.The change of temperature changes the viscosity of resin and the distribution of resin on the surface of prepreg,leading to the change of interlayer slip resistance.The slip resistance between prepregs is positively correlated with the pressure,and the resin layer of prepregs can still play the role of lubrication under 600 k Pa pressure,and the friction mechanism does not change.The interlayer slip behavior of Cycom970 and domestic prepregs was different with increasing temperature.The interlayer slip resistance of Cycom970 and domestic prepregs reached the minimum at about 65℃ and 145℃ respectively.(4)According to the research on the press-operation and interlayer slip behavior of prepreg,comprehensively considering the factors such as temperature process window,pressure timing and pressure size during the autoclaving process,the autoclaving process optimization scheme was developed for two kinds of prepreg at home and abroad respectively,and the scheme was verified by carrying out the manufacture of C-beam small test parts.The results show that the optimized process scheme can significantly improve the wrinkle defects in R-angle area of C-beam test pieces.The proposed process optimization scheme has high feasibility in reducing R-angle wrinkle defects and improving the forming quality of components.